EPA-650/4-74-039
OCTOBER 1973
Environmental Monitoring Series
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EPA-650/4-74-039
LABORATORY
AND FIELD EVALUATIONS
OF
EPA METHODS 2, 6, AND 7
by
Henry F. Hamil
Southwest Research Institute
8500 Culebra Road
San Antonio, Texas 78284
Contract No. 68-02-0626
Task Order 1, Change Order 1
ROAPNo. 26AAG
Program Element No. 1HA327
EPA Project Officer: M.R.Midgett
Quality Assurance and Environmental Monitoring Laboratory
National Environmental Research Center
Research Triangle Park, North Carolina 27711
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
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This report has been reviewed by the Environmental Protection Agency
and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Agency,
nor does mention of trade names or commercial products constitute
endorsement or recommendation for use.
11
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ABSTRACT
A study was made to evaluate Methods 2, 6, and 7, proposed by
the Environmental Protection Agency for determination of stack gas
velocity and volumetric flow rate, sulfur dioxide emissions, and nitrogen
oxide emissions, respectively. These evaluations were conducted prior
to collaborative testing of the subject methods. Findings and conclusions
concerning these methods are given below.
Method 2 - Stack Gas Velocity and Volumetric Flow Rate
Statistical analysis of stack gas velocity data indicates that
Method 2 provides an accurate estimate of the true stack gas velocity at
high gas velocities. Accuracy of Method 2 velocity estimates at low gas
velocities is shown to be unreliable. Correlation analysis demonstrates
that the volumetric flow rate estimates have the same characteristics as
the velocity estimates. Correlation analysis also demonstrates that the
variation in the stack gas velocity and volumetric flow rate estimates is
principally due to variation in determination of Ap.the velocity head in
the stack. By way of comparison, a separate analysis was performed on
individual velocity traverse data.
Method 6 - Sulfur Dioxide
Investigation of possible causes of variation in collection efficiency
of SO, in Method 6 was made. Com entration of SO, in the stack gas is
ill
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shown to be the only factor to have any significant effect on collection
efficiency. The purge period specified in Method 6 was shown to be
necessary to avoid apparent low SC^ values due to retention in the
isopropanol bubbler. The minimum detectable limit is estimated to be
3ppm.
Method 7 - Nitrogen Oxides
Investigation of possible interference with NOX determination by
chloride ion indicated the degree of interference to be linearly related
to chloride ion concentration.
The minimum detectable limit for Method 7 is estimated to be
2ppm NOX as NC>2. The upper limit without dilution is approximately
100 ppm NOX as NC>2. The maximum sensitivity of Method 7 can
approach 0.2 ppm but probably lies between 0.2 ppm and 2.0 ppm NOX as
N02.
iv
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TABLE OF CONTENTS
Page
I. INTRODUCTION 1
II. RESULTS AND CONCLUSIONS 3
Method 2 - Stack Gas Velocity and
Volumetric Flow Rate 3
1. Evaluation of Method 2 3
2. Analysis of Single Traverse Data 23
3. Conclusions 30
Method 6 - Sulfur Dioxide 31
Method 7 - Nitrogen Oxides 41
APPENDICES I, H, III and IV
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LIST OF TABLES
Table Page
1. Operating Characteristics, T.H. Wharton Power 5
Plant, Unit No. 1, Houston Lighting & Power Co.
2. Velocity Traverse Data, Houston Lighting & Power 6
Co., T. H. Wharton Power Plant, Unit No. 1, Low
Fuel Feed Rate
3. Velocity Traverse Data, Houston Lighting & Power 7
Co., T. H. Wharton Power Plant, Unit No. 1,
High Fuel Feed Rate
4. Experimental and Theoretical Gas Velocity and 11
Volumetric Flow Rate - Houston Lighting and Power
Company, T. H. Wharton Plant, Unit No. 1
5. Correlation Coefficients Vs as a Dependent Variable 12
of Various Experimental Parameters
6. Statistical Analysis - Experimental Stack Velocities
and Related Parameters 15
7. Statistical Analysis, Theoretical Stack Velocities and
Related Parameters 21
8. Velocity Traverse Data, Houston Lighting & Power Co.,
T. H. Wharton Power Plant, Unit No. 1, Low Fuel 24
Feed Rate, Single Diameter Traverse
9. Velocity Traverse Data, Houston Lighting & Power Co.,
T.H. Wharton Power Plant, Unit No. 1, High Fuel 25
Feed Rate, Single Diameter Traverse
10. Experimental and Theoretical Gas Velocity and
Volumetric Flow Rate - Houston Lighting and Power 26
Company, T. H. Wharton Plant, Unit No. 1, Single
Diameter Traverse
11. Statistical Analysis, Experimental and Theoretical
Stack Velocities and Related Parameters, Single 27
Diameter Traverse
vi
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List of Tables (cont'd.)
Pae
12. Fractional- Factorial Experiment Design for Five
Variables in Eight Experiments Showing the Values
for Each Independent Variable and the Dependent
Variable 33
13. Intermediate Experimental Data from Fractional-
Factorial Experiment Design 36
14. Statistical Analysis of Fractional-Factorial Design 38
15. Data Tabulation—Interference of Hydrogen Chloride
with NOX Determination - EPA Method No. 7 42
vii
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I. INTRODUCTION
This report describes the work performed and the results
obtained on Task Order No. 1, and Task Order No. 1, Change Order
No. 1, which included evaluation of the methods for the determination
of stack gas velocity and volumetric flow rate, the determination of
nitrogen oxide emissions, and the determination of sulfur oxide emissions
in fossil-fuel fired steam generators (Federal Register, December 23,
1971).
Complete plans were developed for the accomplishment of the
objectives before the experimental work began. These plans were
submitted to the Project Officer by letter dated October 3, 1972, and
received subsequent approval.
The task order required experimental investigation of the
following: Possible sources of error in determination of stack gas
velocity and volumetric flow rate due to calibration of the type S pitot
tube, and determination of precision and accuracy of the method in a
suitable facility in which a theoretical value for velocity could be
obtained.
The laboratory investigation of the sulfur dioxide method included
an investigation of SO£ collection efficiency as a function of changing
concentration, as well as investigation of low recovery of SOj> due to
retention in the isopropanol bubbler.
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The laboratory investigation of the nitrogen oxide method
included an evaluation of the detection limits of the method and an
investigation of possible chloride ion interference in the analysis.
A glossary of appropriate equations and terms used in this
report is given in Appendix I.
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II. RESULTS AND CONCLUSIONS
METHOD 2-STACK GAS VELOCITY AND VOLUMETRIC FLOW RATE
1. Evaluation of Method 2
The stack gas velocity and volumetric flow rate as determined by
Method 2 are used in conjunction with the methods for determination of
specific pollutants to determine the emission rate of those pollutants.
Therefore, evaluation of Method 2 with regard to precision and accuracy
was considered necessary. The experimental program was structured
to allow estimation of the precision and accuracy of Method 2.
Statistical analysis of the data obtained in the experimental program was
performed in order to determine which experimental variables contributed
most to the variation in the stack gas velocity.
Permission was obtained from Houston Lighting and Power Company
to perform a series of measurements at their T. H. Wharton Power Plant.
This plant is a natural gas fired steam generating plant, normally maintained
on hot standby, and is used to balance peak loads. As a result,
arrangements could be made to make velocity traverse measurements at
peak load and at a lower level, to give two different stack velocities during
the evaluation.
The fuel gas feed rate is accurately measured at the T. H. Wharton
plant, and this value, in conjunction with stack gas composition as
determined by Or sat analysis, allows the calculation of theoretical stack
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gas velocities for comparison with the experimentally determined
values. A sample calculation demonstrating the method used to
determine the theoretical stack gas velocity and volumetric flow rate
is shown in Appendix II.
Table 1 tabulates the pertinent operating characteristics of the
power plant unit which was used for field investigations, while Tables 2
and 3 show the data obtained by pitot tube traverses at this facility, at
the two feed rates studied.
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TABLE 1. OPERATING CHARACTERISTICS
T. H. WHARTON POWER PLANT, UNIT NO. 1
HOUSTON LIGHTING & POWER COMPANY
Output: 75 megawatts
Fuel Consumption: 13, 600 cu ft per minute, natural gas
Air Rate: 146,000 cu ft per minute
Steam Rate: 650,000 Ib per hour, 1340 psi, 955°F
Stack Velocity: 52 ft per second
Sample Ports: Two 3-in. ports at 90-degree spacing
are located next to a walkway handrail at the 100-ft level
(above grade). This location is 56 feet (8. 3 diameters)
above the preheaters for the boiler, Two 45-degree elbows
in the vertical stack run affect the flow pattern somewhat,
but the ports are still 24 feet (3. 6 diameters) above the
higher ell so that a reasonably uniform flow pattern should
exist at the existing sample port elevation.
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TABLE 2. VELOCITY TRAVERSE DATA,
HOUSTON LIGHTING & POWER CO. , T. H. WHARTON POWER PLANT,
UNIT NO. 1, LOW FUEL FEED RATE1
Run °v& av*,, s xs *s vs
Date No. Time (in H2O) (in H2O)Z OF OF in H^ %H2O % COZ %O2 Md Mg ^g S(
5/22/73 1 1125-1155 0.275 0.524 266 726 29.83 14.0 8.2 6.4 29.5 27.9 32.2
2 1210-1235 0.285 0.521 252 712 29.82 14.6 8.5 5.0 29.5 27.8 31.9
5/23/73 5 1025-1047 0.245 0.498 255 715 29.78 13.5 7.8 6.5 29.5 28.0 33.6
" 6 1055-1130 0.265 0.513 251 711 29.77 14.0 8.2 6.3 29.5 27.9 31.8
" 7 1135-1200 0.265 0.517 264 724 29.77 14.0 8.2 6.4 29.5 27.9 32.4
Q
:f/hr x 10~<
4.970
4. 937
4.774
4.914
4.911
1
Definition of symbols is given in Appendix I.
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TABLES. VELOCITY TRAVERSE DATA,
HOUSTON LIGHTING k POWER CO. , T. H. WHARTON POWER PLANT,
UNIT NO. 1, LOW FUEL FEED RATE1
Apavg **Vavg Ts Ts p
Date TraNTSe Time ^ ^ °F °R in Hg %H2
%CQ
5/2Z/73 3 1400-1425 0.88 0.912 307 767 29.80 14.9 8.8
4 1428-1455 0.82 0.878 317 777 29.80 14.3 8.4
5/23/73 8 1340-1400 0.89 0.937 300 760 29.73 14.7 8.6
9 1405-1425 0.89 0.937 310 770 29.73 17.1 8.9
V
%0
M
5.5 29.6 27.9 57.6
5.8 29.6 27.9 55.8
4.9 29.5 27.8 59.2
5.4 29.6 27.6 59.8
QS
. , .
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The sample ports, designated east (E) and west (W) are located
90 apart on both stacks A and B (see Figure 1). The total gas flow from
the unit is split at the preheater outlet and vented through the two stacks
Jj;
of 80-in. I. D. Since there is a disturbance approximately 3. 6 diameters
upstream of the sample ports, 24 traverse points were chosen on each
diameter.
The Type S pitot tube was calibrated in a wind tunnel at
Southwest Research Institute. Calibration was performed over a velocity
range of 17 to 70 fps. At velocities in that range, the pitot tube coefficient
C had an average value of 0. 77. Variation of the coefficient over the
P
working range was within the + 5% specified in the method. The coefficient
was determined with each leg of the pitot tube facing the gas flow and
was found to be the same in each case.
Data were taken on two days, at two different generating levels
each day. The higher generating level of 71.0 megawatts was near the
rated peak generating level of 72 megawatts, while the lower level was
40.0 or 41. 5 megawatts. On the second day, two traverses were made
during unit line-out while the generating levels were 39.0 and 42. 0 megawatts.
The remaining lower level generating loads were 40.0 megawatts after
line-out.
Fuel feed rates were 680 MCFH at the 71 megawatt generating level
and 385-390 MCFH at the 40-41. 5 megawatt generating level.
EPA policy is to express all measurements in Agency documents in metric
units. When implementing this practice will result in undue cost or difficulty
in clarity, NERC/RTP is providing conversion factors for the particular
non-metric units used in the document. For this report these factors ure
located in Appendix 1.
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FIGURE 1. T. H. WHARTON PLANT, UNIT NO. 1,
SAMPLE PORT CONFIGURATION
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10
Integrated stack gas samples were taken on each traverse by a
modification of Method 3 in which a squeeze bulb was utilized to
transfer gas from the stack into the gas sample bag. A gas sample tube
was incorporated into the probe bundle, which consisted of the pitot tube
thermocouple, and gas sample tube, with the inlet position near the tip
of the Type S pitot tube. Equal volumes of gas were withdrawn via the
squeeze bulb at each traverse point to provide an integrated gas sample
which was analyzed by Or sat analysis.
The data obtained in the experimental runs are presented in
Tables 2 and 3, along with the experimental values of stack velocity and
volumetric flow rate. Stack velocity and volumetric flow rate were
calculated in accordance with the Federal Register,and the appropriate
equations are given in Appendix I.
In Table 4 are presented the theoretical values of stack velocity
and volumetric flow rate which were calculated using fuel feed rate,
stack gas composition, fuel composition, stack gas temperature and
stack dimensions. Also presented in Table 4 are the experimental values
for stack velocity and volumetric flow rate to allow a visual comparison.
In an attempt to determine which experimental parameters have
the greatest influence on the values for V , a correlation analysis using
the data in Tables 2 and 3 was performed using V as the dependent
s
variable and Ap , ( 'Y A P)avg« Ts. Pg, and Mg as independent
variables.
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TABLE 4 . EXPERIMENTAL AND THEORETICAL GAS VELOCITY
AND VOLUMETRIC FLOW RATE -
HOUSTON LIGHTING AND POWER COMPANY,
T. H. WHARTON PLANT, UNIT NO. 1
Run
No.1
1
2
3
4
5
6
7
8
9
Stack
Designation
A
B
B
A
A
B
A
A
B
Fuel Gas3
Feed Rate
MCFH
390
390
680
680
385
385
385
680
680
Load,
megawatts
41.5
41. 5
71.0
71.0
40. 5
40.0
40. 0
71.0
71.0
V
• Stack Gas Velocity, fps
Experimental
32.2
31. 6
57. 6
55.8
30.3
31.2
31.8
59.2
59.8
4
Theoretical
32.9
31.9
56. 5
59.8
33.6
31.8
32.4
57. 3
56.1
Q
Volumetric Flow
Experimental
4. 970
4. 937
8. 318
8.021
4. 774
4.914
4.911
8. 683
8. 370
Rate, scf/hr x 10
Theoretical5
5.197
5. 134
8.443
8.975
5. 393
5. 130
5. 130
8. 639
8. 348
*Run data are calculated from appropriate diameter traverse data, i. e. , Run 1 from traverses 2AW + 1AE.
Stack designation per Figure 1.
3Fuel gas volume is in cubic feet at 60°F and 1 atmosphere pressure.
^Calculated by the procedure shown in Appendix 1, wet gas basis.
^Calculated by the procedure shown in Appendix 1, dry gas basis.
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12
The correlation coefficients obtained are presented in
Table 5.
TABLE 5. CORRELATION COEFFICIENTS Vs AS A
DEPENDENT VARIABLE OF VARIOUS
EXPERIMENTAL PARAMETERS
Independent Variable, Correlation Coefficient,
X Vs = *(*)
APavg 0.9944
(i~Ap^vg 0.9996
Ts, °R 0.9286
Ps , in. Hg -0.4778
Ms -0.3780
As can be seen from the values in Table 5, the strongest
correlation is obtained with V as a function of (VApL.._ and of
S a. V g
APavg . This correlation analysis shows a very strong linear
relationship between Vg and these two related experimental parameters.
The direct relationship of Vg to the other experimental parameters is
less strong, based upon the correlation coefficients. From the correlation
analysis, one would conclude that the variance in Vg would be most
affected by the variance in (V A Pj » which relates directly back to the
variance in Ap&vg.
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13
To further check this hypothesis, a simple statistical analysis
of the experimental stack velocity and volumetric flow rate along with
Pavg i ( V ^ P^vg' save' ^s« anc* PS was *nade in which the mean,
variance, standard deviation, and percent distribution about the mean at
2s were calculated. The analysis was performed on the run data
presented in Tables 2 and 3.
Percentage distribution about the mean at 2s (i.e., the 95%
'0
2s • 100
confidence level) is defined as . It measures the amount of
x
variation in the experimental data for variable x, expressed as a
percentage of the mean value. Each of the independent experimental
parameters being studied is directly or inversely proportional to Vs in the
Vs equation. Thus, a valid technique for determining the parameters to
which Vs is most sensitive, and to which its variability and its uncertainty
are most closely related, is to compare the percentage distribution about
the mean for Vs to the percentage distributions about the mean for the
various independent experimental variables. For comparison, a similar >
analysis of the theoretical stack velocity was made along with the mole
percent CO2 in the stack gas and the stack gas temperature. These two
parameters were chosen for the latter analysis inasmuch as they are the
two experimentally determined numbers which have the most influence on
the calculation of the theoretical velocity (see Appendix II). The portion
of the analysis pertaining to Qg is included to show the relationship
between Vg and Qg and between Qg and the experimentally determined
parameters.
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14
For the statistical treatment, the data were divided into high
and low levels corresponding to the power generating levels of 71.0
and 40.0-41.5 megawatts.
The results of the analysis are presented in Table 6, showing
the mean, variance, standard deviation, and percentage distribution
about the mean at the 95 percent confidence level.
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TABLES- STATISTICAL ANALYSIS -
EXPERIMENTAL STACK VELOCITIES
AND RELATED PARAMETERS
Fuel Feed
Rate
Variable Mean
x x
Low Vg 31.4
A Qs 4.901xl06
Apavg 0.26
(-/,/V ) 0.51
Tsavg 717
Ps 29.50
Ms 27.9
High Vg 58.1
Qs 8.348x10
APavg °-87
ra^avg 0/92
Ts 768
avg
PS 29'56
Mc 27.8
Variance
s2
0. 57
.0056x 1012
0.0003
0.0001
52.0
0.0
0.005
4.06
0.0735xl012
0.001
0.0004
44.0
0.0023
0.02
Standard
Deviation
s
0. 756
.075 x 106
0.0175
0.01
7.21
0.0
0.07
2.015
0.271 x 106
0.032
0.02
6. 6
0.048
0. 14
Percent Distribution About the Mean
2 s x 100
x
95% Confidence Limits
4.8
3.7
13. 5
3.9
2.0
0.0
0. 5
6.9
6.5
7.4
4.3
1. 8
0. 3
1.0
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16
It can be seen that for /\p , the values of s and s are not
avg
the same at the high and low levels, indicating an inequality of variance
at the levels studied. The percent distribution about the mean for
Ap is + 13. 5 at the low level and + 7. 4 at the high level. The
avg
percent distribution about the mean is related to the repeatability of
the method of measuring Ap . In this particular experiment, however,
avg
the true value of /\p in the stack is not known, and due to normal
variations in process parameters the true value of Ap would be expected
to vary with time. The natural variations in true Ap with time would
contribute to the variance about the mean for the set of runs and as a
result would be incorporated in the percent distribution about the mean,
along with that variance about the mean attributable to the repeatability
of the method.
Since no procedure is available for readily separating the
effects of variation of true Ap with time from the effect of repeatability
of the method in the statistical analysis, the percent distribution about the
mean is considered a measure of the total uncertainty of the experimental
values, and consists of the uncertainty due to variations in true /\p plus
uncertainty due to repeatability of the method. However, it is believed
that the flow conditions in the stacks at the test site are generally
characteristic of conditions encountered in stack velocity measurements,
and as a result, the data developed in this study are representative of the
results which can be expected from use of Method 2.
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17
The percent distribution about the mean for p indicates
avg
that the total uncertainty in Ap is considerably greater at low values
avg
of AP than at high values of Ap • This is not unexpected in view
avg avg
of the behavior of the Type S pitot tube and inclined manometer when
measuring velocity heads in disturbed flows. It has been our experience
that when this measuring system is used in stacks where flow patterns
are disturbed and/or cyclonic, oscillations are set up in the liquid
column of the inclined manometer. The observed oscillations were
0. 2-0. 3 inches of water and were unsymmetric within the observed
range. Readings of Ap at each traverse point are made by a visual
estimate of the average value within the range of oscillation. The
range of oscillation at a particular site does not appear to be a function
of overall velocity. For example, in the study under discussion, the
range of the manometer oscillation was essentially the same at stack
gas velocities of about 31 and 58 fps.
As a result, the relative error in reading Ap is greater at
low values where the range of oscillation of the manometer is
approximately equal to the value of Ap than at high values of Ap
where the range of oscillation is approximately one-half the value of
AP,
A brief study was made during pitot tube calibrations to
determine if a Magnehelic^'differential pressure gauge, which
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18
incorporates small orifices in the pitot line connections to provide
damping of sudden transient pressures, was a suitable substitute for the inclined
manometer. The flow in the wind tunnel was intentionally disturbed to
simulate stack gas flow conditions. Even though the Magnehelic gauge
is damped, resulting /\p measurements were no better than those
obtained with an inclined manometer inasmuch as the Magnehelic
gauge showed the characteristic oscillations described above.
Even though the total uncertainty in Z\p appears rather
avg
large at the lower values observed, the effect on the total uncertainty
of the experimental stack velocity is minimized to a fair extent by
the fact that ("/Z\p) is used in the calculation of the velocity. The
O
calculation of ( YAp)a from the individual Ap values measured at
each traverse point is a transformation that both stabilizes the data
and minimizes its random measurement variation. As can be seen
in Table 6, equality of variance is not obtained for (V/!\p)avg over
the range studied. Instead, s and s appear to be a function of the
level of (V/Ap)avg. This is further shown by examination of the
percent distribution about the mean for ( V/\p ) at the high and
O
low levels, where it can be seen that the total uncertainty is -f 3.9%
at the low level and f 4. 3% at the high level. When the experimental
stack velocity data in Table 6 are examined, it can be seen that s2 and s
also are a function of the level of Vg. The percent distribution about
the mean velocity at the high and low levels is + 6. 9 and + 4. 8, respectively.
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19
These values are in iair agreement with the similar values for
("v & p) at the high and low levels, as would be expected from the
avg
highly linear relationship of these two variables indicated in the
correlation analysis . The percent distribution about the mean for Q at
the high and low levels is +_6.5 and _+ 3.7, respectively. These values
correspond favorably with those same values for Vs and (iA p) .A
O
correlation analysis using Qg = f(V&) gives a correlation coefficient of
0.9984, indicating a strong linear relationship between Qs and Vg, which
establishes the dependence of Qs on those same parameters upon which
Vs is dependent.
The other parameters used to calculate V are T M »
S S(avg) 8
and P . The correlation analysis showed poorer linear correlation
between these variables and V . This is supported by the statistical
analysis of these parameters. As can be seen in Table 6, the percent
distribution around the mean for these variables is small, indicating that
the total uncertainty is small, and when variations in process parameters
are considered to occur, this implies good repeatability for the
determination of T , p , and M . Thus it would appear that the
s/ . s s
experimental parameter which most affects the value of V is (V~AP)
s avg
The theoretical stack velocities were calculated as shown in
Appendix II. From the calculation method used, it can be seen that the
calculated theoretical velocities are dependent upon carbon in the fuel,
carbon in the stack gas, fuel feed rate, stack gas temperature, and stack
dimensions .
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20
Fuel carbon analyses and fuel feed rates were provided by
Houston Lighting and Power Company, and no estimate of accuracy
or repeatability for these values is available. Fuel feed rates were
measured with a calibrated orifice meter and were reported as cubic
feet at 60°F and 1 atmosphere pressure. Carbon in the feed was
calculated from a gas chromatographic analysis of the fuel gas and
was reported as Ib-atoms carbon per Ib-mole fuel gas.
Carbon in the stack gas was obtained from the Orsat analysis
of the integrated gas sample taken on each run. Stack temperature
was also determined experimentally on each run. These two variables
were subjected to statistical analysis along with the theoretical
velocities.
In Table 7, it can be seen that the percent distribution about
the mean for the theoretical velocity at the high and low levels is jf 5.8
and+_ 4.6, respectively. The percent distribution about the mean for the
theoretical volumetric flow rate at the high and low levels is + 6.4 and
+ 4.4, respectively. The percent distribution about the mean for CO,
•v. £
concentration at the high and low levels is +_ 5,0 and + 6.1, respectively.
The distribution about the mean for Tg at the high and low levels is
•f 1.8 and +2.0 percent, respectively. These values would appear to
indicate that the experimental variable with greatest effect on the
calculated values of theoretical velocities is the CC»2 content of the stack
gas as determined by Orsat Analysis and that the accuracy of this
experimental value is reflected in the accuracy of the theoretical velocities
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TABLE 7. STATISTICAL ANALYSIS,
THEORETICAL STACK VELOCITIES AND
RELATED PARAMETERS
Percent Distribution About the Mean
Standard
Fuel Feed
Rate
Low
Variable
x
V
Q
%CO0
Mean
x
32.
5.
8.
5
197xl06
2
Variance
0.
0.
0.
56
013xl012
062
Deviation
s
0.
0.
0.
75
113 x 106
25
L s
x 1UO
x
95% Confidence
4.
4.
6.
6
4
1
Level
717
52.0
7.21
2.0
High
V
57.4
2.75
1.66
5. 8
%co2
Q
T_
8.7
8.601x10
768
0.
0.
05
077 xlO12
44
0.
0.
6.
22
277 x
6
106
5.
6.
1.
0
4
8
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22
Statistical analysis performed on the volumetric flow rate
data indicates they are primarily dependent on the stack gas velocity.
The accuracy, repeatability and distribution about the mean for
volumetric flow rates appear to be a direct function of the same
parameters as for the velocity data.
In order to assess the accuracy of Method 2 determination of
stack gas velocity, a comparison was made between the experimental
and theoretical stack gas mean values at both the high and low levels.
The details of the test are shown in Appendix 4.
At the low level, there was a significant difference between the
experimental and theoretical mean values. At the high level, no
significant difference between the experimental and theoretical mean
values was indicated.
Based upon the assumption that the theoretical mean values
represent the true stack gas velocities, velocity determinations by
Method 2 as written provide a reasonable estimate of stack gas velocity
at high velocity levels. However, at low velocity levels, the method does
not provide a good estimate of stack gas velocity.
Since the statistical treatment previously described indicated that
the accuracy and repeatability of Qg appear to be a direct function of
the same parameters as Vg, the above assessment of accuracy remains
valid for Qs at high and low levels.
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23
2. Analysis of Single Traverse Data
As shown in the previous section, the limits of accuracy with
which Ap can be measured at the individual traverse points will be the
predominant factor in determining the accuracy of the values obtained
for V , over the range studied.
8
It is believed that since the experimental stack velocity may be
influenced by both time dependent variations due to changes in process
parameters and by unsymmetrical flow geometry in the stack, a more
accurate estimate of the repeatability of the procedure for determinating
velocity could be obtained by statistical analysis of the data determined
from traverses of a single diameter. The use of two diameter traverses
may give a more accurate estimate of the time average velocity than a
single diameter traverse, but it also has the effect of smoothing the data
since it represents an averaging process.
Tables 8 and 9 show the data obtained on single diameter pitot
tube traverses at low and high fuel feed rates. In Table 10 are summarized
the experimental and theoretical velocities and volumetric flow rates for
single traverses at both the high and low fuel feed rates.
The results of analyzing the single traverse data are shown in
Table 11. For the experimental stack velocity, V , since the earlier
avg
analysis indicated that Ap and (V Ap) are the dominant variables
avg avg
in determining precision of the estimate, only these two parameters were
analyzed in the single traverse data.
-------
TABLE 8 . VELOCITY TRAVERSE DATA ,
HOUSTON LIGHTING & POWER CO. , T. H. WHARTON POWER PLANT,
UNIT NO. 1. LOW FUEL FEED RATE
Single Diameter Traverse
A
avg
J. i cl-VCi
Date Run No
5/22/73 1-AE
2 -AW
3-BE
4-BW
5/23/73 9-AE
" 10-AW
" 11-BE
" 12-BW
13-AW
14-AE
DC *-*
. Time
1125-1135
1145-1155
1210-1220
1225-1235
1025-1030
1035-1047
1055-1108
1115-1130
1135-1145
1151-1200
0.22
0. 33
0.25
0.32
0.23
0.26
0.27
0.26
0.27
0.26
(in ^Ojfc
0.475
0. 573
0.494
0. 547
0.475
0. 521
0.515
0. 510
0.522
0.512
°F
265
266
254
250
252
258
251
250
263
264
M
°R
725
726
714
710
712
718
711
710
723
724
a
in Hg
29. 84
29. 82
29.82
29. 82
29.78
29.77
29.77
29.77
29.77
29.77
%H20
13.9
14. 1
14.4
14.7
13.3
13.6
14.2
13.8
14.5
13.5
%C02
8. 1
8.2
8.4
8.6
7.7
7.9
8.3
8.0
8.6
7.8
%02
6.6
6. 1
5. 1
4. 8
7.0
6.0
5.9
6.6
6.8
5.9
Md
29. 5
29. 5
29. 5
29. 5
29. 5
29. 5
29. 5
29.5
29. 6
29.4
Ms
27.9
27.9
27.8
27.8
28.0
27.9
27.9
27.9
27.9
27.9
Vs
f a.vg scf/hrvirr6
29. 1
35. 2
30. 1
33.2
28. 8
31. 8
31.4
31.0
32. 1
31.4
4. 59
5.52
4. 80
5.29
4. 65
5.07
5.03
4.98
5.03
4.98
CM
-------
TABLE 9. VELOCITY TRAVERSE DATA,
HOUSTON LIGHTING k POWER CO. , T. H. WHARTON POWER PLANT,
UNIT NO. i, HIGH FUEL FEED RATE
Single Diameter Traverse
Traverse avS
Date No. Time (inH2O)
5/22/73 5-BW
11 6-BE
11 7-AW
11 8-AE
11 15-AE
11 16-AW
11 17-BE
• " 18-BW
1400-1412
1415-1425
1428-1440
1445-1455
1340-1348
1353-1400
1405-1415
1418-1425
0. 91
0.85
0.84
0.80
0.90
0.88
0.88
0.89
(^>'av
(inH20)^
0.951
0.873
0.911
0.845
0.943
0.930
0.935
0.938
g Ts Ts
°TT °R
a t\.
306 766
308 768
317 777
316 776
286 746
314 774
310 770
310 770
Ps
in Hg
29.80
29.80
29.80
29.80
29.73
29.73
29.73
29.73
%H20
14.9
14.9
14.8
13.8
14.7
14.7
19.6
14.5
%C02
8.8
8.8
8.7
8. 1
8.6
8.6
9.3
8.5
%02
5.2
5.7
5.4
6.2
4.8
5.0
4.6
6.1
Md
29.6
29.6
29.6
29.5
29.5
29.5
29.6
29.6
Ms
27.9
27.9
27.9
27.9
27.8
27.8
27.3
27.9
Vs Q
avg s
fps scf/hr x ID'6
60.0
55. 1
58. 1
53. 6'
58. 9
59.4
60.0
59.5
8.84
8.09
7.54
7.90
8.92
8. 66
8.30
8. 75
CM
-------
TABLE 10. EXPERIMENTAL AND THEORETICAL GAS VELOCITY
AND VOLUMETRIC FLOW RATE -
HOUSTON LIGHTING AND POWER COMPANY,
T. H. WHARTON PLANT, UNIT NO. 1
Single Diameter Traverse
Traverse
No.1
1-AE
2-AW
3-BE
4-BW
5-BW
6-BE
7-AW
8-AE
9-AE
10-AW
li-BE
12-BW
13 -AW
14-AE
15-AE
16-AW
17-BE
18-BW
Fuel Gas2
Feed Rate
MCFH
390
390
390
390
680
680
680
680
385
385
385
385
385
385
680
680
680
680
Load,
megawatts
41. 5
41. 5
41.5
41. 5
71.0
71.0
71.0
71.0
39.0
42.0
40.0
40.0
40.0
40.0
71.0
71.0 "
71.0
71.0
Stack Gas Velocity, fps
Experimental
29. 1
35.2
30. 1
33.2
60. 0
55. 1
58. 1
53. 6
28. 8
31. 8
31.4
31.0
32. 1
31.4
58. 9
59.4
60.0
59.5
Theoretical^
33.3
32.9
31.7
31.0
57. 1
57.2
58. 5
62.7
33.7
33.2
31. 5
32.5
31.4
33.9
56.7
58.8
55.3
59.1
Volumetric Flow Rate, scf/hr x 10"^
Experimental
4. 59
5. 52
4. 80
5.29
8. 84
8.09
7. 54
7. 90
4. 65
5.07
5.03
4.98
5.03
4. 98
8. 92
8. 66
8.30
8.75
Theoretical'1
5.26
5. 19
5. 07
4. 96
8. 44
8. 44
8. 54
9.27
5.46
5. 32
5. 07
5.26
4. 95
5. 39
8. 64
8. 64
7. 99
8. 74
Letters on run numbers are sample port designation per Figure 1.
^ Fuel gas volume is in cubic feet at 60°F and 1 atmosphere pressure.
^Calculated by the procedure shown in Appendix 1, wet gas basis.
4Calculated by the procedure shown in Appendix 1, dry gas basis.
-------
TABLE 11. STATISTICAL, ANALYSIS, EXPERIMENTAL
AND THEORETICAL STACK VELOCITIES
AND RELATED PARAMETERS,
SINGLE DIAMETER TRAVERSE
EXPERIMENTAL
Percent Distribution About the Mean
Fuel Feed
Rate
Low
High
THEORETICAL
Low
High
Variable Mean
X X
Vs 31.4
^avg °'27
(•/A~)av o.5i
V 58. 1
s
Ap 0.87
favg
(VA~) 0.92
P avg
V 32.5
o/,, c*r*\ Q •>
/o *-'*-' ^ o. £
Ts, °R 717
V 58.2
%C02 8.7
TH, °R 768
Variance
s2
3.58
0.0012
0.0009
5. 82
0.0013
.0014
1.09
0. 102
44. 3
4.91
0. 110
97.3
Standard
Deviation
s
1.89
0.035
0.030
2.4
0.036
0.037
1.05
0. 32
6. 60
2.22
0.34
9.90
2 s x 100
X
95% Confidence Level
12.2
25.8
11. 6
8.3
8.2
8.0
6.4
7.8
1.8
7.6
7.8
2.6
ISJ
-------
28
As can be seen by comparison of Tables 6 and 11, the results
are considerably different when single diameter traverse data are
analyzed and compared to the results obtained from analysis of Method 2
data. In Table 11, it can be seen that there is equality of variance for
AP . When the data from two traverses are combined as specified
avg
in Method 2, equality of variance is not observed due to the smoothing of
the data. For the Method 2 analysis, distribution about the mean for
Ap is +. 13.5 percent at the low level, while in the single traverse
6
data the distribution about the mean for Ap at the low level is + 25.8
avg -
percent. However, at the high level, the corresponding distributions
about the mean are + 8.2 percent for single traverse data and +7.4 percent
for the Method 2 data, indicating that the repeatability of the determination
of Ap is better at higher velocities, and little smoothing of data
avg
occurs by averaging data from two traverses.
Comparison of the analysis of (VZ^p) ' indicates that a similar
o
apparent improvement in repeatability of (yAp) is obtained by
avg
averaging the results of two diameter traverses. For the Method 2
results, distribution about the mean for ( T/Ap) is + 3. 9 and + 43
avg - '
percent at the low and high levels, respectively, while for the single
traverse data, the similar values are f 11. 6 and + 8.0, respectively.
As can be seen, equality of variance is not obtained for (-/An)
^ avg
and the variance of (/Ap) is a function of the level of (//V)
avg avg
-------
29
Analysis of Vg for the single traverse data indicates that
the distribution about the mean at the low and high levels is + 12.2 and
4- 8. 3 percent, respectively, which corresponds closely with the
distribution about the mean for ( 7A _.) 'at the low and high levels.
P avg
This would be expected from the linear relationship between Vg and
( vZAp)a indicated by the correlation analysis described earlier.
tr o
Also shown in Table 11 are the results of analysis of the
theoretical velocity, percent CO^i and T based on single diameter
traverse data. The relationships previously described indicating a
major dependence in the distribution about the mean for V on the
distribution about the mean for percent CO^ still appear valid, with
the apparent repeatability being somewhat poorer as shown by the
increased distribution about the means for the single traverse data
shown in Table 11 when compared to the similar data for Method 2
shown in Table 7.
-------
30
3. Conclusions
Based upon this study, the following conclusions have been made.
The experimental stack velocity and volumetric flow rate are primarily
dependent upon the accuracy with which Ap is determined during the
velocity traverse, over the velocity range studied. Under field conditions,
using a Type S pitot tube and inclined manometer, measurements of
Ap can be made which provide values of stack velocity with a percent
distribution about the mean of +_ 8. 3 to jf 12. 2, over the velocity range
studied, based upon single diameter traverse data. The percent
distribution about the mean for the velocity calculated according to Method 2
is + 4.8 to + 6 . 9 over the velocity range studied.
Even though velocities calculated according to Method 2 using data
from two diameter traverses 90° apart have a smoothing effect on the data
and shorten the distribution interval about the mean, when compared to
single traverse data, accuracy analysis indicates that Method 2 as written
provides reliable estimates of stack gas velocity at high flow rates, but
that the estimates at low velocities are unreliable. This unreliability is
directly attributable to the large variability in the determination of Ap
at low velocities . Thus, if greater accuracy or repeatability in determining
the experimental stack velocity is desired, the most profitable area for
improvement would appear to be in improving the accuracy of measuring
Ap in the stack.
-------
31
METHOD 6 - SULFUR DIOXIDE
The sulfur dioxide section called for an investigation of possible
variation in collection efficiency with changing concentration over the
applicable range of the method and also for an investigation of the
possibility of low recovery of sulfur dioxide due to retention in the
isopropyl alcohol bubbler. Accordingly, a special experiment was
designed to evaluate these effects along with some other relatively
important factors. The details of the experiment and the results are
given below.
Collaborative testing of this method is anticipated at the facilities
of Walden Research and Monsanto Research, in accordance with plans
and subcontract arrangements already submitted to the Project Officer.
At the Dayton power plant, the only control of sulfur dioxide level which
can be obtained is through the addition of dilution air to the flue gases.
At Walden, control of the sulfur content of the fuel will make it possible
to obtain varying SO2 levels in the flue gas without dilution. For this
reason, a collaborative test at each location is considered preferable.
Anticipated collaborators include Monsanto Research, Walden
Research, Southwest Research Institute (Houston laboratory) and
Southwest Research Institute (San Antonio laboratory). With some
crowding, a fifth collaborator could be accommodated, and several air
pollution control agencies are being contacted to see if a voluntary
participant can be obtained.
-------
32
To study the effect of the independent variables on the dependent
variable (observed concentration expressed as a percent of the gas
standard concentration), a quarter replicate factorial test plan was
designed. Statistical analysis of the test data should identify which
independent variables cause significant effects.
The independent variables studied were the sulfur dioxide
concentration (397 ppm or 707 ppm), the number of sets of peroxide
impingers in series (one or two), the number of isopropyl alcohol
bubblers in series (one or two), the sampling time (20 or 30 minutes),
and the sample volume (0.75 or 1.0 cubic feet). Variations in sample
flow rate were thus accomplished. The dependent variable was defined
as the observed concentration expressed as a percent of the expected
value according to the gaseous standards which were used. Since the
specific design used investigated seven variables in eight experiments,
and only five were specified, the remaining two were dummy variables.
The dummy variables are unassigned factors and are used to obtain
an estimate of the variance. The combinations for each experiment
are shown in Table 12 along with the value of the dependent variable.
Before discussing the results, it is important to clarify
the independent variables and to describe the manner in which
intermediate data were generated.
The two levels for the concentration were provided by two
separate cylinders of sulfur dioxide in nitrogen (397 ppm and 707 ppm)
-------
33
TABLE 12. FRACTIONAL-FACTORIAL EXPERIMENT DESIGN
FOR FIVE VARIABLES IN EIGHT EXPERIMENTS SHOWING
THE VALUES FOR EACH INDEPENDENT
VARIABLE AND THE DEPENDENT VARIABLE
Experiment IPA Peroxide Observed
Number Bubblers Impingers Concentration Time Volume Recovery
1 2
2 1
3 1
4 1
5 1
6 2
7 2
8 2
2 sets
2
1
2
1
1
1
2
707 ppm
397
397
707
707
707
397
397
20
30
20
20
30
30
20
30
1.00 99.7
0. 75
1.00
0.75
100. 3
94. 5
94. 5
1.00 90.7
1.00 97.0
0.75 102.8
-------
34
which were analyzed (using the West-Gaeke method) by the supplier
with accuracy of 0. 5 percent quoted for each. The experiments were
conducted shortly after receipt of the standard gases. Compatibility
with system dynamics was achieved by charging a Tedlar bag from the
respective cylinder and then sampling immediately from the bag. A
commercially produced stack sampling apparatus was not available during
the work; therefore, the train was assembled from individual components
meeting the specifications shown in Figure 6-1 of Method 6 in the
Federal Register. The probe and the pitot tube were not required for
sampling from Tedlar bags.
For experiment numbers 3 and 5, the bubbler-impinger portion
of the train was identical to Figure 6-1 of the method. In this config-
uration, measurements show the vacuum at the suction end of the train
to be 17 to 20 inches of water for flow rates of 1 to 1. 5 liters per minute.
When two isopropyl alcohol bubblers were called for (experiment
numbers 1, 6, 7, and 8), an additional bubbler containing 15 ml of
80 percent isopropyl alcohol was inserted in series into the train
following the first isopropyl alcohol bubbler. When two sets of peroxide-
filled midget impingers were called for (experiment numbers 1, 2, 4, and 8),
two impingers charged with 15 ml of three percent hydrogen peroxide
followed by one empty impinger were inserted in series into the train
following the empty midget impinger. For example, experiment numbers
1 and 8 contained two midget bubblers charged with isopropyl alcohol
-------
35
followed by two midget impingers charged with hydrogen peroxide
followed by one empty midget impinger followed by two more peroxide
impingers followed by another empty impinger.
The midget impingers charged with peroxide were treated in sets
containing two filled impingers and one empty so that the procedure as
described in Sections 4.2 and 4. 3 of the method could be applied to
each set independently. A result was thus generated and recorded
for each set and the two were added and converted to the percentage
of the expected value to produce the final result (the dependent variable).
There is a distinct advantage in this approach since another independent
estimation of collection efficiency can be made using experiment
numbers 1, 2, 4, and 8 by comparing the contents of the second set
of impingers with the first. These data are shown in Table 13, and
the results will be discussed subsequently.
The contents of the isopropyl alcohol bubblers were not
discarded as per the method but were analyzed for sulfur dioxide by
an improvised procedure to oxidize any retained SC>2 to 803 and then
determined by titration as in Section 4. 3 of the method. The contents
of each of the bubblers were analyzed separately, and results were
expressed in terms of percent recovery of the gaseous sample so that
a material balance of the entire train was easily accomplished by
simple addition. These percentages were not added into the dependent
-------
36
TABLE 13. INTERMEDIATE EXPERIMENTAL DATA
FROM FRACTIONAL-FACTORIAL
EXPERIMENT DESIGN
Peroxide Impingers
1st 2nd Total
Experiment
Number
1
2
3
4
5
6
7
8
IPA
1st
1. 1
0. 5
0
0
2.0
1.0
0. 5
0.8
Bubblers
2nd
1.7
-
-
-
-
0. 1
0. 5
2. 5
91.7
99.0
100.3
94.5
94. 5
90.7
97.0
102.8
0.2
0.7
0
91.9
99.7
100.3
94. 5
94. 5
90.7
97.0
102. 8
#Numbers represent percentage of expected value based on concentration
of gas standard.
variable. The data are shown in Table 13. In order to confirm that
the contents of the bubblers represented retained SO2 rather than any
SO, present in the sample, a series of experiments was run in which
the bubbler contents were not oxidized but rather titrated directly so
that any sulfur oxides detected would be attributable to SO3 rather than
retained SO£. The results (not shown) showed no detectable SO3 in
any of the bubblers in any of eight runs. Therefore, the respective
results shown in Table 13 are assured to be due to SO2 retention.
These results will be discussed in more detail later.
-------
37
The two levels of time and sample volume are straightforward.
The actual selection of the times and volumes are based on the minimum
time and minimum volume as designated in the Federal Register under
Section 60.46(c)(2), Test Methods and Procedures. The various
combinations of sample time and sample volume produce flow rates
of 0.71, 0.94, 1.06, and 1.42 liters per minute.
Mechanical difficulties were encountered throughout the experi-
ments,necessitating the repeating of some of the runs one or more times.
These difficulties were associated with pump leakage, meter malfunction,
or loose connections. It is, therefore, very important to make the leak
check as described in Section 4. 1. 1 of the method.
Another difficulty encountered was in the carryover of isopropyl
alcohol which often occurred at sample flow rates which were
about 1.4 liters per minute (1 cu ft in 20 min) such as in experiment
numbers 4 and 7.
The results of the statistical analysis are given in Table 14.
The table shows the net effect [the difference between the average value
of responses at the high (+) level and the average value of responses
at the low (-) level] for each variable. The significance of each effect
(with respect to the dependent variable) is indicated by the absolute value
of the t-statistic and the corresponding percentage probability. The
significance percent for each effect thus provides an estimate of the
probability of finding an effect that large due to chance or experimental
-------
38
TABLE 14. STATISTICAL, ANALYSIS OF
FRACTIONAL-FACTORIAL DESIGN
jC
Youden Ruggedness Test
Plackett-Burman Design for 7 Factors and 8 Experiments'
System - Method 6
Response - Recovery
Variable
No.
1
2
3
4
5
6
7
Variable
Name
Dummy
IPA Bubblers
Impinge rs
Dummy
Concentration
Time
Volume
Effect
(- to +)
-1.30
-1.65
-1.60
1.55
-7.05
1.00
-1.90
|t| -Value
0.85
1.08
1.05
1.02
4.62
0.65
1.24
Significance
Percent
42
32
34
35
0.8
>50
25
Average value of response = 96.425
Standard error = 1. 5266
Degrees of freedom = 2
* Youden, W. J. , "The Collaborative Test,"!, of the A.O. A. C. , 46, No. 1,
(1963), pp 55-62.
Plackett, R. L. and Burman, J. P. , "Design of Optimum Multifactoral
Experiments," Biometrika, 33, (1946), pp 305-325.
-------
39
error alone. If the effects of one or more dummy variables were
significant, there would be either (1) significantly large interactions
of main effects, (2) important independent variables omitted or not
held constant, or (3) considerable error in the measurement technique.
The only effect sufficiently large to be significant (10 percent
level of significance) is the concentration. The effect is negative,
indicating a decreased response in going from the low level to the high
level. In the absence of data from the second set of peroxide impingers
from experiment numbers 1 and 4, this might be interpreted as a
decrease in collection efficiency at the higher concentration level.
Since the second set of impingers contains little or no sulfur dioxide
(see also experiment numbers 2 and 8 at the lower concentration level),
plus the fact that there is not a sufficiently significant effect from
peroxide impingers (the effect is even in the wrong direction), the
natural conclusion is that the higher concentration is very probably
in the neighborhood of 660 ppm. The importance of retrieval of inter-
mediate data now becomes evident.
To summarize the results thus far: there are no significant
effects due to isopropyl alcohol bubblers, peroxide impingers, time,
volume, or dummy variables. The effects of concentration are either a
concentration bias in the method or an inaccuracy in the concentration
of the 707 ppm cylinder. Unfortunately, at the time of report preparation,
the 707 ppm standard was no longer available for independent analysis.
-------
40
The effects of sulfur dioxide retention in the isopropyl alcohol
bubblers are negligible from the analysis above and are also minor
according to the data in Table 13. The average retention in a bubbler
is less than one percent of the amount present (average of 0. 9 percent
for 12 observations). The values can be seen to range from zero to
2. 5 percent at the highest. All of these results were obtained using
the 15-minute purge as specified in Section 4. 1.2 of the method. A
single experiment (under the same conditions as experiment number 1)
in which the purge was not done showed 7 percent retention in each of
the two bubblers for a total of 14 percent. It is, therefore, quite
important to follow the purging procedure rigorously.
The minimum detectable limit (based on a net titration of 0. 1 ml,
a 0. 75 ft sample, and a 10 ml aliquot) is 3 ppm which should cause
no limitations in the use of the method. If more sensitivity was desired,
a larger sample could be taken. The method can conveniently analyze
samples up to 1400 ppm (based on 50 ml titration, 0.75 ft sample,
10 ml aliquot), providing the collection efficiency does not deteriorate
at that level.
-------
41
METHOD 7 - NITROGEN OXIDES
Laboratory work was conducted to check out the entire procedure
and especially to investigate the reported interference from hydrogen
chloride. A total of 64 experimental tests were made using standard
nitric oxide mixtures of 98 and 700 ppm.
In 48 tests comprising five sets of experiments, the 98 ppm
standard gas was used as a test gas in flasks which were spiked with
hydrogen chloride of known concentration. Concentrations of hydrogen
chloride were 11 ppm, 50 ppm, 100 ppm, 500 ppm, and 1120 ppm.
In two sets, the spiking was done using hydrochloric acid of known
concentration while in the other three sets, spiking was accomplished
by injecting the proper amount of dry hydrogen chloride gas.
In 16 other tests, the 700 ppm test gas was used, half without
hydrogen chloride and half with the addition of sufficient hydrochloric
acid to give a hydrogen chloride concentration of 700 ppm. All
samples were analyzed according to the procedures described in
EPA Method 7.
Table 15 and Figure 2 presents the results obtained.
Based on these results and the complete laboratory data, the following
conclusions are established concerning Method No. 7:
1. The method is tedious and time consuming, especially in
the analytical phase. This, of course, was known previously
and has been the subject of some discussion and comment.
-------
42
TABLE 15. DATA TABULATION—INTERFERENCE OF HYDROGEN
7
CHLORIDE WITH NO DETERMINATION - EPA METHOD NO.
X.
ANALYSIS
HC1
Cone, by Sample
Chloride Vol. Serial
Date Set Source PPm No.
11/16/72 1 hydrochloric 1120 1
acid 2
3
4
5
6
7
8
Avg.
11/20/72 2 hydrochloric 11 9
acid 10
11
12
13
14
15
16
Avg.
11/21/72 3 dry hydrogen 500 17
chloride 18
19
20
21
22
23
24
11/27/72 500 25
26
27
28
29
30
31
32
Avg.
Stand.
NO
ppm
Vol.
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
Spiked
NO
Cone.
ppm
--
__
--
15
20
20
__
18
__
--
--
-_
95
97
94
97
96
61
65
52
56
73
83
__
61
_ _
_ _
--
--
69
62
55
62
64
Unspiked
NO
Cone.
ppm
110
121
-.
116
__
__
--
—
103
112
108
105
--
--
--
--
w M
_ _
_ _
__
_ _
_ _
_ ..
102
100
97
95
--
- -
..
_ _
-------
43
Table 15. Data Tabulation--Interference of Hydrogen Chloride
with NO Determination - EPA Method No. 7 (Cont'd.)
ANALYSIS
HC1
Cone, by Sample
Chloride Vol. Serial
nate Set Source ppm No.
jl/29/72 4 dry hydrogen 100 33
chloride 34
35
36
37
38
39
40
Avg.
12/5/72 5 dry hydrogen 50 41
chloride 42
43
44
45
46
47
48
Avg.
7^/6/72 6 hydrogen chloride 700 49
50
51
52
53
54
55
56
iZ/H/72 hydrogen chloride 700 57
1 58
59
60
61
62
63
64
Avg.
Stand.
NO
ppm
Vol.
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
700
700
700
700
700
700
700
700
700
700
700
700
700
700
700
700
700
Spiked
NO
Cone.
PPm
--
- -
--
__
83
82
79
82
82
--
--
—
91
88
89
89
89
--
--
--
447
412
502
469
--
--
--
--
--
429
521
409
456
Unspiked
NO
Cone.
ppm
89
f\ 4
91
91
90
--
--
--
--
91
92
92
90
--
--
--
--
943
841
917
847
--
--
--
--
602
--
712
545
--
--
--
«• ^
-------
Actual NOX concentration in
all runs = 98 ppm
o Cone, as NO ppm
200
400
600 800
HC 1 ppm
1000
1200
1400
Figure 2. Interference of HC1 With the Determination of NOX —
EPA Method No. 7, Average Points
-------
45
2. Results are affected by the presence of hydrogen chloride,
as has been indicated by previous publications. The degree of
interference is approximately linear with hydrogen chloride
concentration, ranging as high as 78 percent with
1120 pprn HC1 when sampling a test gas of approximately
100 ppm NO . A similar relationship appears to apply in the
case of the 700 ppm test gas, although tests were only run at a
single level of HC1, 700 ppm. At this level, the indicated NOX
level is about 65 percent of the original value as determined
in tests without hydrogen chloride. It should be noted that
erratic results were obtained with the unspiked 700 ppm samples.
The sensitivity of the method along with the minimum detectable
limits for NOX by this method have been estimated. Data used in
the calculations of the minimum detectable limit were taken from a
calibration curve constructed by analysis of a series of standard
solutions of potassium nitrate. Concentration range of the standards was
zero to 400 (j.g nitrogen dioxide. Measured absorbance of the solutions
was in the range of 0-0. 5 absorbance units, using absorbance cells of
1.2 centimeter path length. The calculations are presented in Appendix III.
The minimum detectable limit is estimated to be 2 ppm NOX as NCK in
the gas sample. The upper limit without dilution is about 100 ppm
NOX as NO2 in the gas sample. To analyze gas samples containing
around 700 ppm NOX would require a tenfold dilution according to Section 4. 3. 1
of the method (Appendix III, Figure 1).
-------
46
The maximum sensitivity of the method can approach 0. 2 ppm
NOX provided the absorbance can be read to 0.001 absorbance units,
but in a practical sense would probably be between 0. 2 and 2. 0 ppm NOX.
-------
I-i
APPENDIX I
Glossary of Terms and Equations
Terms and equations taken from The Federal Register,
Volume .36, December 23, 1971:
Equations
(V8)a = Average Stack Gas Velocity, ft/sec
Q = Stack Gas Volumetric Flow Rate, ft /hr
Qs = 3600 (1 - B > ,=- Jbr VSA
Terms
= Conversion constant : K = 85.48
sec L/b-mole
= Pitot tube coefficient, dimensionless
P
= Average velocity head of stack gas
avg
,
g— )
K/
L it i /\ , where >1 = number of traverse points
in 'l / *—*P;
ayg i~T7
/^\ \ = Average of the square roots of the velocity head
\ P/avor measurements taken at individual traverse points
i =n
"~)
/avg
(J/\ 1 = _L \ v^p.» where lr\ = number of traverse points
\ P/avg n ' i
i = 1
-------
1-2
(Ts)avg = Average absolute stack gas temperature, R
I
(Ts) = —- y *• i, where y\ = number of traverse points
5 f i ••
i = 1
Tstd = Absolute temperature at standard conditions, 530°R
= Absolute stack gas pressure, inches mercury
P . , = Absolute pressure at standard conditions, 29.92 inches
mercury
B = Proportion by volume of water vapor in the stack gas
= Dry molecular weight of the stack gas (calculated from
Orsat analytical data)
M = Molecular weight of the stack gas, wet basis
M = M, (1 - B ) + 18 B
s d x wo' wo
B. Terms and equations used in statistical analysis of data:
'i - y)
i = i
Correlation Coefficient =
y (
,/
i = i
_ 2
^ - y)
where x is the independent variable and y is the
dependent variable, i.e. y = f(x)
-------
1-3
x is the arithmetic mean of variable x
x = — \ xj, where )^ is the sample size
i = 1
2 xt-'
s is the unbiased estimate of the population variance, O
' -^ - x) , where x and )\ as above
i = 1
is the sample standard deviation
8 =
Percent distribution about the mean, 95 percent confidence level
is defined as
2s • 100 , . ,
, s and x as above
x
t-value is a student's t with six degrees of freedom
t = effect
standard error
C. Conversion Factors:
inches x 2. 540 = centimeters
cubic feet/unit time x 0.0283 = cubic meters/unit time
feet per second x 0. 3048 = meters per second
pounds/unit time x 0. 4536 = kilograms/unit time
feet x 0. 3048 = meters
-------
II-l
APPENDIX II
DATA FROM T. H. WHARTON POWER PLANT,
HOUSTON LIGHTING AND POWER COMPANY
Sample calculation of theoretical stack velocity and volumetric flow rate.
Carbon in fuel gas, calculated from gas chromatographic analysis: 1.072 Ib-
^f
atom carbon/lb-mole fuel gas. . Carbon in stack gas, from Orsat Analysis
Run 1-AE, Table 1: 0.081 Ib-atom carbon/lb-mole stack gas.
mole dry stack gas/mole fuel gas in:
i-072 = 13.24
0.081
moles H2O = 2 x moles CO2 = 2x0.081 = 0.162
Total moles stack gas/mole fuel gas in:
13.24 + (0. 162)(13. 24) = 1.162x13.24 = 15.38
Theoretical gas velocity, wet basis:
3 T
Total moles stack gas Fuel feed rate, ft /hr _ s
X
moles fuel gas in (Stack area, ft^)(3600 sec/hr) T, ,
XX16J. £cl S
moles stack gas 390 x JO3 ft3/hr 725°R
5'38 moles fuel gas in X (69.81 ft2)(3600 sec/hr) X 520°R
= 33.3 fps
Theoretical volumetric flow rate, dry basis:
moles dry stack gas c , , , . ,^3 ,. 530°R
• <-——:—a— x fuel feed rate, ft^/hr x ~
moles fuel in Tfuel gas
where:
530°R = 70°F = EPA specified temperature
13>24 moles dry stack gas x 39Q x 1Q3 ffc3/hr x 530^
moles fuel in 520 R
= 5.26x 106ft3/hr.
* 96.2% methane.
-------
ni-i
APPENDIX III
Estimation of Limits for NOX by Method 7
The approximate minimum detectable limit for NO by Method 7
can be estimated from laboratory data and the appropriate equations for
calculating the concentration of nitrate in the samples.
Ref. : Method 7, Section 6.2, Federal Register, Vol. 36,
p. 24893, 23 December 1971.
lb
r _ m cuft \ _/.,.. -5 Ib/scf U m
c -
where C = cone, of NO (as NO-,), Ib/scf
x £
m = mass of NO£ in gas sample, |o.g
V = sample volume at standard conditions, ml.
sc r
V = 200 ml
sc
According to Sections 3.3.4 and 5.2, the calibration curve is
prepared using diluted standard solutions with a concentration range of
0 ^ m ^ 400 (jig. The resulting calibration curve in our laboratory gives
806 [ig NO^/absorbance unit, using absorption cells of 1.2 cm path length.
Therefore, an absorbance of 0. 010 is equivalent to 8. 06 (xg NO2 and
C = -2000- = 25 x 10-8 = 0.25 x 10-6
lb 359 ft3/r^mole 530°R 10 ft
° 6 3
46 lb/l>.-.nuie X ^92°R million ft3
ppm = C x (8.4 x 106)
ppm = (0.25 x 10-6) x (8.4 x 106) = 2. 1 ppm
A concentration of 2 ppm NO£ in the gas sample is probably
detectable.
-------
ni-2
A maximum sensitivity of about 0.2 ppm is possible if absorbance
can be measured to 0. 001 absorbance unit.
As shown in Figure 1, the upper limit of gas sample NOX
concentration without dilution is about 100 ppm based on an absorbance of
0. 5 unit.
-------
Ill-3
1.0
u
c
-------
IV-1
APPENDIX IV
Accuracy of Method 2
To assess the acuracy of the experimentally determined
Method 2 stack gas velocities with respect to the theoretical stack gas
velocities, a Student's t-test is used to obtain a significance level.
Assume Vtheoretical represents the true stack gas velocity.
Then, using a calculated t-value
V" V
tc = savg " theoretical
s
where s is the sample standard deviation of Vs and >^
O
is the number of observations of Vc used to obtain Vs
savg avg
The significance level resulting from the test will be the probability
of obtaining a sample (experimental) mean Vs which differs from the
avg
true (theoretical) mean %eoreUcal by a magnitude of | V^ - Vtheoretic
or greater due to chance alone. The probability is obtained from a table
of Student's t distribution with ( ^- 1) degrees of freedom. A low
significance level, less than 10 percent, indicates that v*0 is not a
savg
good estimate of Vtheoretical.
1. Low Level
The hypothesis to be tested is that JJL = 32. 5 (Vfcn . .).
From Table 6 , Vg =31.4 with a sample standard deviation s = 0.756.
avg
-------
IV-2
Then,
31.4 - 32. 5
c 7 (0. 756)/
-1. 1
tc " 0.337
tc = -3. 264 with 4 degrees of freedom
From the Student's t table, the percent significance level for tc = -3.264
with four degrees of freedom is 3. 49%.
2. High Level
The hypothesis to be tested is that p. = 57. 4 (Vtheoretical).
From Table 6 , Vg = 58. 1 with a sample standard deviation s =2.015.
avg
Then,
58. 1-57.4
tc =
(2.015)/
0.7
1.0075
tc = 0. 695 with 3 degrees of freedom
From the Student's t table, the percent significance level for tc = 0. 695
with three degrees of freedom is 56. 08%.
-------
TECHNICAL REPORT DATA
_ (Please read liiitnii-tiiins on //.v /vrt rsc before eomi'lciiiii;)
•• REPORT NO 2
EPA-650/4-74-039
4. TITLE AMD SUBTITLE
"Laboratory and Field Evaluations of EPA Methods
2, 6, and 7."
'. AUTHOR(S)
Henry F. Hanril
*. PERFORMING ORGANIZATION NAME AND ADDRESS
Southwest Research Institute, 8500 Culebra Rd.,
San Antonio, Texas 78284
|!Z. SPONSORING AGENCY NAME AND ADDRESS
Environmental Protection Agency, NERC, QAEML
Methods Standardization & Performance Evaluation Branch
Research Triangle Park, N. C. 27711
S. SUPPLEMENTARY NOTES
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
October 1973
6. PERFORMING ORGANIZATION CODE j
8. PERFORMING ORGANIZATION REPORT NO. I
SWRI Project 01-3462-001
10. PROGRAM ELEMENT NO.
1HA327
11. CONTRACT/GRANT NO.
68-02-0626
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
6. ABSTRACT ! ~~ ~~" ' ~
A study was made to evaluate Methods 2, 6, and 7, proposed by EPA for
determination of stack gas. velocity and volumetric flow rate, sulfur dioxide emissions,
and nitrogen oxide emissions. These evaluations were conducted prior to collaborative
testing of the subject methods. Method 2: Stack Gas Velocity and Volumetric Flow Rate:
Statistical analysis of stack gas velocity data indicates tnat Method 2 provides an
accurate estimate of the true stack gas velocity at high gas velocities. Accuracy of J
Method 2 velocity estimates at low gas velocities is shown to be unreliable. Correlation
analysis demonstrates that the volumetric flow rate estimates have the same character- j
Tstics as the velocity estimates. Correlation analysis also demonstrates that the I
variation in the stack gas velocity and volumetric flow rate estimates is principally j
due to variation in determination of Ap, the velocity head in the stack. By way of
^mparison, a separate analysis was performed on individual velocity traverse data. |
' 6 - Sulfur Dioxide: Investigation of possible causes of variation in collection
of S02 in Method 6 was made. Concentration of SO? in the stack gas is shown
o be the only factor to have any significant effect on col lection efficiency. The
Purge period specified in Method 6 was shown to be necessary to avoid apparent low S02
values due' to retention in the isopropanol bubbler. The minimum limit is estimated to
Je 3 ppm. Method 7-Nitrogen Oxides; Investigation of possible interference with NO
germination bychloride ion indicated the degree of interference to be-linearly re*-
>eerttration.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
DlsTRlBUTION STATEMENT
limited
b.lDENTIFIERS/OPEN ENDED TERMS
COSATI Held/Group
19. SECURITY CLASS (/VIM Keport)
Unclassified .
21. NO. OF PAGfcS
62
2220-1 (9-73)
20. SECURITY CLASS ( Hiis page)
Inclassified
22.
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