Handout
Plant Inspection
and Evaluation Workshop
Opacity as an Indicator
of Control Equipment Performance
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF ENFORCEMENT
OFFICE OF GENERAL ENFORCEMENT
WASHINGTON, D.C. 20460
April 1979
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DRAFT
OPACITY AS AN INDICATOR OF
CONTROL EQUIPMENT PERFORMANCE
by
Kirk E. Foster
U. S. ENVIRONMENTAL PROTECTION AGENCY
Office of Enforcement
Division of Stationary Source Enforcement
Washington, D. C. 20460
and
Gary L. Saunders
PEDCo Environmental, Inc.
505 South Duke Street
Durham, North Carolina 27701
November 1978
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USE OF OPACITY IN EVALUATING AIR POLLUTION CONTROL
EQUIPMENT OPERATING AND MAINTENANCE PRACTICES
Measurement of plume or stack opacity can be a useful
tool in determining whether air pollution controls are
operating properly. Air pollution sources are usually
subject to regulations limiting the plume opacity in addi-
tion to mass emission rates or concentration standards. The
opacity standards established by the U.S. Environmental
Protection Agency, however, are generally set less stringent
than the mass emission standards so that a violation of the
opacity will be a clear indication of the decline in the
efficiency of the control equipment and presumably a viola-
tion of the mass emission standards. Although agency field
inspectors are generally less concerned with opacity levels
which do not exceed the opacity limitations, these opacity
levels may be used as tools to indicate the performance of
the control equipment. The presence of a noticeable plume
or unexplained changes in opacity even in the low opacity
ranges may signify deterioration in control equipment opera-
tion or changes in the process or raw material conditions
which adversely affect control equipment performance.
Opacity of an effluent is an intrinsic property of the
plume and, depends upon the concentration of the particulates
in the gas stream as well as the particle size and other
optical properties. Although the physical and chemical
characteristics of particulate emissions may differ appre-
ciably between source categories and even somewhat from
process to process within a given source category, for most
individual sources there is sufficient stability in these
optical properties to develop reliable opacity-mass emission
correlations. Opacity-mass emission relationships have been
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developed and reported in the literature for a number of
source categories with a high degree of correlation.
Opacity measurements may be made either instrumentally
(transraissometer) or by a qualified observer using EPA
Method 9. Unless there is physical or chemical secondary
formation of particulates in the plume as it leaves the
stack, the visual measurement has been shown to agree closely
with the in-stack transmissometer measurement. The visual
measurements tend, in general, to be lower than the instru-
mental measurements. This is due to the negative bias
and/or low sensitivities of the observer method when evalu-
ating plumes under viewing conditions where plume visibility
is less than desired for the method. Also, the observer may
have difficulty in determining slight changes in opacity at
very low levels of less than 5% opacity. The transmissome-
ter or opacity monitor with its higher measurement sensitiv-
ities would be able to detect slight changes in the low
opacity range and would, of course, provide a continuous
measurement of opacity when use of visual methods is not
possible. Although the visual method is acceptable for
making gross estimates of the performance of a control
device, the transmissometer is more ideally suited for use
in determining proper operation and maintenance of air
pollution control devices. The remainder of this discussion
will largely pertain to in-stack opacity measurements by
transmissometry and its use in determining the level of
performance achieved by a control device.
Ensor and Pilat have developed a theoretical method for
calculating plume opacity from the properties and concentra-
tion of the particulate matter in the plume (Attachment 1}.
Use of constants (K) that have been developed experimentally
from the effluent characteristics improves the reliability
of the theoretical method. Once a suitable calibration
curve of adequate reliability is developed, it is possible
to monitor the process emissions on a continuing basis with
2
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opacity monitor measurements.
A similar variation of the basic Beer-Bougert law for
the transmittance of light through a plume has been developed
by Conner* and is shown below. The K factor used in the
equation developed by Conner is different in that it is the
reciprocal of the K values reported by Ensor and Pilat.
_ Iff T
% opacity = (1 - e * m ) x 100
where:
2
„ _ attenuation meter
J\ —
mass concentration gram
C = mass concentration gram/meter
m
L = path length of opacity measurements meters
or:
I %_0£\
r - -In U - 100 f
m ~ (K) (L)
Figure 1 presents graphical relationships that have
been developed for various source categories and the mass
concentration (g/m ) of the particulate matter. In this
figure, the value of K is simply the slope of the line
m
(—). If the plume path length is known as well as the
opacity, then an estimation of particulate mass-concentration
can be performed.
Figure 2 presents an empirical method of determining a
K-value for emissions of an asphalt concrete plant con-
trolled by a baghouse. The value of K is found by determin-
ing the slope of the line utilizing linear regression tech-
niques. It should be noted that the term "extinction coeffi-
cient" is used here interchangeably with "attenuation coeffi-
cient" .
* ESRL, US EPA, Research Triangle Park, N.C. 27711.
-------
UJ
0.22
0.20
0.18
0.16
0.14
o
u
* 0.12
»| 0.10
•
L
I < 0.08
•
r
0.06
0.04
0.02
0
ATTENUATION
IASS CONCENTRATIO
3
1.S
( ) = NUMBER OF SOURCES STUDIED
GRAPH PREPARED BY WILLIAM CONNER.
ENVIRONMENTAL SCIENCE AND RESEARCH LAB.
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, N.C.
0.5
ci
2
_
m
0.2S
0.02
0.04
0.06 0.08 0.10
MASS CONCENTRATION, g/m3
0.12
0.14
0.16
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OPACITY - MASS CONCENTRATION RELATIONSHIP
OF THE ASPHALTIC CONCRETE PLANT EMISSIONS
,30
CSJ
cn .20
>-
I—
t—I
o
o
.10
20% Opacity
EPA Report No. 650/2-74-120
In-Stack Transmissometer Measurement
of Participate Opacity and Mass Concentration
November 1974
K = .33
I
I
.16
.19
.32 >43 .48 .64
MASS CONCENTRATION (GRAMS METER"
FIGURE 2
.80
.36
.32
.28
.24
.20
.16
.12
.08
.04
oo
O
O
o
.96
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Figure 2 also brings attention to another point. In
the case of this asphalt plant, opacity levels above 10%
would indicate a violation of NSPS limitations if they were
applicable. However, as mentioned previously, slight varia-
tions in opacity at these low-levels may not be detectable
by an observer. Detecting levels below five percent opacity
would almost always entail the use of a transmissometer.
The expected levels of particulate concentrations as
clear or near clear stack conditions are approached are
highly variable between source categories and processes
within categories, because of the optical properties of the
particulate matter. For example, a pulverized coal-fired
boiler is predicted to approach 0.02 gr/ACF at clear stack
conditions whereas aluminum Soderburg processes are much
more sensitive and levels are predicted to be between .001
to .003 gr/SCF. A greater degree of control may be required
to achieve clear stack conditions.
The use of an in-stack transmissometer is more ideally
suited to checking proper operation and maintenance of ESPs
and baghouses than it is to checking wet-scrubbers. Scrub-
bers present a problem of entrained water droplets which
interfere with correct opacity readings. Selection of a
monitor with narrow-band light filtration to avoid H.O
interferences is one approach for monitoring scrubbers.
Another approach is stack reheat to avoid water droplets.
An inexpensive single-pass transmissometer may be used to
indicate leaking bags as well as to optimize cleaning cycles
for baghouses (Attachment 6). Transmissometers may also be
used to "fine-tune" the rapper sequencing of electrostatic
precipitator to avoid excessive reentrainment of particulate
matter. There are usually no problems of water vapor in-
volved in these processes.
A number of attachments are included which discuss in
further detail some of the topics covered in this discussion.
A bibliography of material to provide background information
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concerning optical properties of particulates, measurement
techniques, and opacity-mass emission correlations is also
included.
In summary, the use of opacity should be considered not
only as a tool to indicate the compliance of the source with
opacity regulations, but as an indication of operation and
maintenance procedures and for identifying potential problems
and deteriorating performance in the control equipment. The
use of an in-stack transmissometer is more ideally suited to
this task than visual methods, particularly at low opacity
levels. As long as the monitor is installed properly and
maintained it should provide both the source and the agency
with an indication of the control equipment's long-term
performance.
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Bibliography of Opacity Measurement Literature
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OPACITY AND OPTICAL PROPERTIES OF AERSOLS
Ensor, David S., and Michael J. Pilat. The relationship between the visibil-
ity and aerosol properties of smoke-stack plumes. Department of Civil Engineering,
University of Washington, Seattle, Wash.
Spaenkuch, D. Atmospheric scattering functions in connection with the size
distribution of haze according to Jung's exponential law. FTD-HT-23-340-69,
Foreign Technology Division, Wright Patterson Air Force Base, September 1969.
Pilat, M. J., and D. S. Ensor. Plume opacity and particulate mass concen-
trations, Atmos. Environ. 4:163-173, 1970.
Ensor, D. S., and M. J. Pilat. The effect of particle size distribution on
light transmittance measurement. American Industrial Hygiene Association
Journal 32:287-292, May 1971.
Pilat, M. J., and D. S. Ensor. Comparison between the light extinction aero-
sol mass concentration relationship of atmospheric and air pollutant emission
aerosols. Atmosph. Environ. 5:209-215, May 1971.
Ensor, D. S., and M. J. Pilat. Calculation of smoke plume opacity from par-
ticulate air pollutant properties. JAPCA 21:496-501, August 1971.
Cornett, C. L. Plume opacity. M.S. thesis. Department of Civil Engineering,
Cincinnati University, Cincinnati, Ohio, 1972.
Ensor, D. S. Smoke plume opacity related to the properties of air pollutant
aerosols. Ph.D. thesis. University of Washington, Seattle, Wash., 1972.
Peterson, C. M., and M. Tomaides. In-stack transmissometer technique for
measuring opacities of particulate emissions from stationary sources. Environ-
mental Research Corporation, St. Paul, Minn. EPA-R2-72-099, U.S. Environmental
Protection Agency, NTIS PB 212-741, April 1972.
Ensor, D. S., and M. J. Pilat. Calculation of smoke plume opacity from par-
ticulate air pollutant properties. JAPCA. Reprint presented at 13th conference
on methods in air pollution and industrial hygiene studies, University of Cali-
fornia, Berkeley, Calif., October 30-31, 1972.
Franz, I., and J. Kraus. The influence of forward scattering on measurement
of the degree of transmission of aerosols. Staub Reinhaltung der Luft, vol. 33,
no. 9, September 1973.
Ensor, D. S., L. D. Bevan, and G. Markowski. Application of nephelometry to
the monitoring of air pollution sources. Presented at the 67th annual meeting
APCA, Denver, Colo., 1974.
Hermann, Jorg, and Hans Jorg Eiberweiser. The influence of particle size
in extinction measurements. Staub Reinhaltung der Luft. vol. 34, no. 5, May 1974.
Wolbach, C. Dean. Approximations to discrepancies between visual and instru-
ment opacity readings for submicron particulate material. Env. Sci. and Tech.
8:458-459, May 1974.
11
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Hallow, J. S., and S. J. Zeek. Prediction of Ringeltnann number and optical
characteristics of plumes. JAPCA 23:676, 1974.
Ensor, D., and M. Pilat. The correlation of plume opacity to particulate
mass concentration. Presented at 78th national meeting of American Institute
of Chemical Engineers, Salt Lake City, Utah, August 18-21, 1974.
Conner, W. D. Measurement of the opacity and mass concentration of particu-
late emissions by transmissometry. EPA-650/2-74-128, EPA National Environmental
Research Center, U.S. Environmental Protection Agency, Research Triangle Park,
N.C., November 1974.
Pilat, Michael J. Plume opacity related to particle properties. Paper
presented at PNWIS-APCA meeting, Boise, Idaho, November 18-19, 1974.
Reisman, £., W. D. Greber, and N. D. Potter. In-stack transmissometer meas-
urement of particulate opacity and mass concentration. EPA Contract Report 68-
02-1229, EPA National Environmental Research Center, EPA-650/2-74-120, U.S.
Environmental Protection Agency, Research Triangle Park, N.C., November 1974.
Avetta, Edward D. In-stack transmissometer evaluation and application to
particulate opacity measurement. Owens-Illinois, Inc., Pittsburgh, Pa. EPA-650/
2-75-008, U.S. Environmental Protection Agency, NTIS PB 243-402/AS, January 1975.
Weir Jr., Alexander, Dale G. Jones, and Lawrence T. Paypay. Measurement of
particle size and other factors influencing plume opacity. Paper presented
at the International Conference on Environmental Sensing and Assessment, Las
Vegas, Nev., September 14-19, 1975.
Fenn, R. W. Optical properties of aerosols. In Handbook on Aerosols. Edited
by R. Dennis. U.S. Energy Research and Development Administration TID-26608, 1976.
Harkowski, Gregory R., George J. Woffinden, and David S. Ensor. Optical
method for measuring the mass concentration of particulate emissions. Environ-
mental Protection Technology Series, EPA-600/2-76-062, U.S. Environmental Pro-
tection Agency, March 1976.
Weir Jr., A., et al. Factors influencing plume opacity. Env. Sci. and
Tech. 10:539-544, June 1976.
Pilat, M. J., and J. E. Thielke. Plume opacity related to particle size
and chemical composition (progress report). EPA grant R8038 97-02, February 1977.
Weir Jr., Alexander. Clearing the opacity issue. Env. Sci. and Tech.. vol. 11,
no. 6, June 1977.
12
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IN-STACK INSTRUMENTAL MEASUREMENT TECHNIQUES
Jahnke, J. A., and G. J. Aldina. Continuous Monitoring for Source Emissions.
U.S. Environmental Protection Agency, Research Triangle Park, N.C. EPA Contract 68-
02-2378.
James, J. E. The use of a transmissometer as a process control tool to con-
trol emissions from a high efficiency electrostatic precipitator (undated report).
Wostradowski, R. A. Continuous particulate monitoring of hog-fuel fired power
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General Federal procedures concerning control of emissions from stationary
sources as per paragraph 4.1 of the Federal Air Quality Act. German Federal Republic
Sera, G. J. , et al. Particulate mass: A summary report. State of the art:
1971, Instrumentation for Measurement of Particulate Emissions from Combustion
Sources, vol. I, NTIS PB 202-655, Springfield, Va.
Yocom, J. E. Problems in judging plume opacity: A simple device for
measuring opacity of wet plumes. JAPCA 13:36, January 1963.
Buhne, Karl-Wilhelm. Investigators into the directional dependence of photo-
electric smoke density measuring instruments. Staub Reinhaltung der Luft,
vol. 31, no. 7, July 1971.
McKee, Herbert C. Instrumental method substitutes for visual estimation of
equivalent opacity. JAPCA 21:488-490, August 1971.
Cornett, C. L. Plume opacity. M.S. thesis. Department of Civil Engineering,
Cincinnati University, Cincinnati, Ohio, 1972.
Ensor, D. S. Smoke plume opacity related to the properties of air pollutant
aerosols. Ph.D. thesis. University of Washington, Seattle, Wash., 1972.
Peterson, C. M., and M. Tomaides. In-stack transmissometer technique for
measuring opacities of particulate emissions from stationary sources. Environ-
mental Research Corporation, St. Paul, Minn. EPA-R2-72-099, U.S. Environmental
Protection Agency, NTIS PB 212-741, April 1972.
Gunther, Rainer. An optical smoke density meter for direct indication of the
amount of solid:
September 1973.
2
amount of solids per m flue gas. Staub Reinhaltung der Luft. vol. 33, no. 9,
Cristello, J. C., and J. E. Walther. An evaluation of an on-stack transmis-
someter as a continuous particulate monitor. Presented at the 67th annual
meeting APCA, Denver, Colo., 1974.
Ensor, D. S., L. D. Sevan, and G. Markowski. Application of nephelometry to
the monitoring of air pollution sources. Presented at the 67th annual meeting
APCA, Denver, Colo., 1974.
Schneider, W. A. Opacity monitoring of stack emissions: A design tool with
promising results. In Electric Utility Generation Planbook 1974, New York:
McGraw-Hill, 1974.
13
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Nader, J. S., F. Jaye, and W. Conner. Performance specifications for sta-
tionary source monitoring systems for gases and visible emissions. EPA-650/2-74-
013, U.S. Environmental Protection Agency, January 1974.
Pfister, Ewald. An integration instrument for timewise evaluation of emis-
sions. Staub Reinhaltung der Luft, vol. 34, no. 2, February 1974.
Beutner, Heinz P. Monitoring of particulate emissions from cement plants.
Rock Products. May 1974.
Wolbach, C. Dean. Approximations to discrepancies between visual and instru-
ment opacity readings for submicron particulate material. Env. Sci. and Tech.
8:458-459, May 1974.
McKee, Herbert C. Texas regulation requires control of opacity using instru-
mental measurements. JAPCA. vol. 24, no. 6, June 1974.
Schneider, W. Evaluating particulate emission problems through opacity
monitoring. Stack-Sampling News, July 1974.
Ensor, D., and M. Pilat. The correlation of plume opacity to particulate
mass concentration. Presented at 78th national meeting of American Institute
of Chemical Engineers, Salt Lake City, Utah, August 18-21, 1974.
Beutner, H. P. Measurement of opacity and particulate emissions with an on-
stack transmissometer, JAPCA, vol. 24, no. 9, September 1974.
Conner, W. D. Measurement of the opacity and mass concentration of particu-
late emissions by transmissotnetry. EPA-650/2-74-128, EPA National Environmental
Research Center, U.S. Environmental Protection Agency, Research Triangle Park,
N.C., November 1974.
Cristello, J. C., and J. E. Walther. An evaluation of an on-stack transmis-
someter as a continuous particulate monitor. Paper presented at PNWIS-APCA
meeting, Boise, Idaho, November 18-19, 1974.
Reisman, E., W. D. Greber, and N. D. Potter. In-stack transmissometer meas-
urement of particulate opacity and mass concentration. EPA Contract Report 68-
02-1229, EPA National Environmental Research Center, EPA-650/2-74-120, U.S.
Environmental Protection Agency, Research Triangle Park, N.C., November 1974.
Walcher, Hans. Digital intergrator to smooth the signals of instruments
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no. 12, December 1974.
Instrumentation for Environmental Monitoring, 1st ed. Environmental Instru-
mentation Group, Lawrence Berkeley Laboratory, University of California, Berke-
ley, Calif., 1975, part 2.
Avetta, Edward D. In-stack transmissometer evaluation and application to
particulate opacity measurement. Owens-Illinois, Inc., Pittsburgh, Pa. EPA-650/
2-75-008, U.S. Environmental Protection Agency, NTIS PB 243-402/AS, January 1975.
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John, Walter. Investigations of particulate matter monitoring using contact
electrification. Environmental Protection Technology Series, EPA-650/2-75-043,
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Cristello, J. C., and J. E. Walther. Continuous onstack monitoring of par-
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fabric filter on a spreader stoker utility boiler. Report presented at the 69th
annual meeting APCA, Portland, Ore., June 27-July 1, 1976.
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15
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Hood, K. T., et al. Measuring plume opacity. TAPPI 60:141, 1977.
Buhne, Karl-Wilhelm, and Wolfgang Jockel. Local and temporal distribution
of dust content in flue gas channels of larger steam boiler plants. Staub Rein*
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77-124, U.S. Environmental Protection Agency, August 1977.
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16
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OPACITY/MASS EMISSIONS MEASUREMENTS: SPECIFIC SOURCE CATEGORIES
James, J. E. The use of a transmissometer as a process control tool to con-
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Stoecker, Wilbert F. Smoke-density measurement. Mech. Eng., October 1950.
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continuous monitoring of particulate emissions from lignite fired boilers.
Paper presented at the Second Int. Clean Air Congress. Int, Union of Air
Poll. Prevention Assoc., Washington, D.C., December 6-11, 1970.
Buhne, K. K., and L. Duwel. Continuously recording surveillance of dust emis-
sions in the cement industry with the RM4 instrument. Staub Reinhaltung der Luft
32:329-334, 1972. (Summary of test results available from Lear Siegler, Inc.)
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Buhne, Karl-Wilhelm, and Ludwig Duwel. Recording dust emission measurements
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Ferguson, R. A. Feasibility of a C. W. Lidar technique for measurement of
plume opacity. Stanford Research Institute, EPA-650/2-73-037, U.S. Environ-
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Rodriguez, D. G. Measuring opacity of cat cracker flue gas. Chem. Eng.
Profile 69:62-63, December 1973.
Schneider, W. Evaluating particulate emission problems through opacity
monitoring. Stack-Sampling News, July 1974.
Ensor, D., and M. Pilat. The correlation of plume opacity to particulate
mass concentration. Presented at 78th national meeting of American Institute
of Chemical Engineers, Salt Lake City, Utah, August 18-21, 1974.
Cristello, J. C., and J. E. Walther. An evaluation of an on-stack transmis-
someter as a continuous particulate monitor. Paper presented at PNWIS-APCA
meeting, Boise, Idaho, November 18-19, 1974.
17
-------
Hood, K. T., and A. L. Caron. The relationship between particulate mass
emission rate and observed plume appearance from Kraft recovery furnaces.
Paper presented at PNWIS-APCA meeting, Boise, Idaho, November 18-19, 1974.
Reisman, E., W. D. Greber, and N. D. Potter. In-stack transmissometer meas-
urement of particulate opacity and mass concentration. EPA Contract Report 68-
02-1229, EPA National Environmental Research Center, EPA-650/2-74-120, U.S.
Environmental Protection Agency, Research Triangle Park, N.C., November 1974.
Fuirheller, W. R., and T. L. Stewart. Visible emission measurements at
asphalt roofing plants. Monsanto Research Corporation, Dayton, Ohio. Report
76-ARM-ll. U.S. Environmental Protection Agency Contract 68-02-1404. (Two
reports: 1975 and 1976).
Cristello, J. C., and J. E. Walther. Continuous onstack monitoring of par-
ticulate proves feasible. Pulp and Paper, May 1975.
Shofner, F. M., G. Kreikebaum, and H. W. Schmitt. In situ continuous measure-
ment of particulate mass concentration. Paper presented at 68th annual meeting
APCA, Boston, Mass., June 5-20, 1975.
Walton, John M., Ernest C. Koontz, and I. R. Mclnnis. Air pollution in
the woodworking industry. Tennessee Division of Air Pollution Control, Nash-
ville, Tenn. Report presented at the 68th annual meeting APCA, Boston, Mass.,
June 15-20, 1975.
Visible emission operations. Kaiser Steel Corporation. EPA-330/2-75-010,
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Knapp, K. T., W. D. Conner, and R. L. Bennett. Physical characterization
of particulate emissions from oil-fired power plants. In Proceedings of the
Fourth National Conference on Energy and the Environment. Am. Inst. of Chem.
Eng., Dayton, Ohio, 1976, pp. 495-500.
Conner, W. D. A comparison between in-stack and plume opacity measurements
at oil-fired power plants. In Proceedings of the Fourth National Conference
on Energy and the Environment. Am. Inst. of Chem. Eng., Dayton, Ohio, 1976.
pp. 478-483.
Ensor, D. S., R. G. Hooper, R. C. Carr, and R. W. Scheck. Evaluation of a
fabric filter on a spreader stoker utility boiler. Report presented at the 69th
annual meeting APCA, Portland, Ore., June 27-July 1, 1976.
Hood, K. T., A. L. Caron, and R. 0. Blosser. Variability observer and
instrument recorded plume opacity from Kraft recovery furnaces equipped with
high efficiency electrostratic precipitator. National Council of the Paper
Industry for Air and Stream Improvement. Report presented at the 69th annual
meeting APCA, Portland, Ore. June 27-July 1, 1976.
Chang, Daniel P. Y., and Bradford C. Grems. Transmissometer measurement of
particulate emissions from a jet engine test facility. JAPCA, vol. 27, no. 7,
July 1977.
-------
Hood, K. T., and T. F. Briody. Evaluation of the performance and applicabil-
ity of a laser light backscattcr measurement instrument to the monitoring of a
particulate concentration prior to and exiting a Kraft recovery furnace electro-
static precipitator (special report). National Council of the Paper Industry for
Air and Stream Improvement, December 1977.
Nader, John S. Impact of sulfuric acid emissions on plume opacity. U.S.
Environmental Protection Agency. Presented at the Symposium on Transfer and
Utilization of Particulate Control Technology, Denver, Colo., July 23-28, 1978.
-------
ATTACHMENTS
Calculation of Smoke Plume Opacity from Particulate Air
Pollutant Properties, Ensor, D.S. and Pilat, M.J., APCA
Journal, Vol. 21, No. 8, August 1971.
IGCI Consensus Report on Industrial Emission Levels
Producing "Clear" or "Near Clear" Stacks, APCA Journal,
Vol. 23, No. 7, July 1973.
Measurement of Opacity and Particulate Emissions with an
On-Stack Transmissometer, Beutner, Heinz P., APCA
Journal, Vol. 24, No. 9, September 1974.
Instrumental Method Substitutes for Visual Estimation of
Equivalent Opacity, McKee, Herbert C., APCA Journal,
Vol. 21, No. 8, August 1971.
Opacity Monitoring Technique Predicts Baghouse Mainten-
ance, Saltz, J. and Cotler, L., Pollution Engineering,
November 1978.
Continuous On-Stack Monitoring of Particulate Proves
Feasible, Cristello, J.C. and Walther, J.E., Pulp and
Paper, May 1975.
Impact of Sulfuric Acid Emissions on Plume Opacity,
Nader, J.S. and Conner, W.D., Symposium on Transfer and
Utilization of Particulate Control Technology, Denver,
CO, July 23 - 28, 1978.
Charts from Evaluation and Collaborative Study of Method
for Visual Determination of Opacity of Emissions from
Stationary Sources, Hamil, H., EPA 650/4-75-009, January
1975.
21
-------
Calculation of Smoke Plume Opacity from
Partfculate Air Pollutant Properties
D. S. Ensor and M. J. Pllal
University of Washington
Calculation of $mok« plum* opacity from m« properties of tfw particulato emission
it facilitated with the use of a parameter K (specific portieutete volume cm'/m1/
extinction coefficient m~') computed from theory. Graph* of K vs. me geometric
matt mean particle radius at geometric standard deviations from I (monodis-
perie) lo 10 are presented for particle refractive indices of 1.96-0.66i (carbon),
2.80-0.02i, 1.33 (water) and 1.50 at a wavelength of light of 550 nm. Experi-
mental data of K for various sources are reported. Application to the estimation
of the Ringelmann number is discussed and illustrated with an example.
Nomenclature
* extinction coefficient per volume of
aerwol
(r) particle number fraction frequency
distribution
/ intensity of transmitted light
ft intensity of incident light
I /It light transmitUnce
I <-!)»»
K spn-ific particulate volume /extinc-
tion coefficient ratio
L illumination path length or di-
trneler uf plume
m refractive index of particle relative
to air
•i real part of refractive index
•• imaginary part ol refractive index
»{r) particle Dumber freijiienry distribu-
tion, which, multiplied by the
radius increment, f particles between r and r
t Jr
Qt extinction efficiency factor
r particle riidius
Tf, (scornclric numlwr mean radius
rr* £'•', metric mass mean radius
Up .-pocilic projected area or tlic specific
extinction area
It" total parti«'iil:ile ina.is concentration
Grttk
size parameter, 2rr/Jk
wavelength uf light
3.MI5!)
average purtirle density
particle size geometric tUndard
deviation
introduction
Air Pollution Rofulationt
Regulations to control particulate air
pollution from sources are usually of the
following types:
1. visible emissions (Ringflmann
No.);
2. [articulate matter concentration
grain loading (grains/scf);
3. process weight code (Ib partitu'aie
emission/It) process weipht);
4. boundary line atmospheric aerosol
coBicentrations (micrograinM/'cubic
meter).
A detailed discussion of the various
air pollution regulations and the com-
munities imph'incnlinj; them ran be
found ih Stem.1 The rvi;iil;itioii of
sources by visible evaluation of the
cnu--ioH |j|ume o|xicity (Kinjirlniann
No. limit) U the lo:ist time i-un.-iiming
nnd loast exjionsive nH'th(MJ for a control
iim'iicy to itnpk'tnent. For these
reasons llini;elniuiin numltrT ohservu-
tiuiii are friH|iiently used to control
Miurces. In Table I the Hitim-lnintm
number, plume opacity, uiul /ructioiiuj
light lrut>suuUam-e arc ronijiared.
Ringelmann numbers are used by an ob-
server to describe black smoke plume*,
and equivalent opacity i* used for white
or colored plumes.
A relationship between the plume
opacity and the particle )>liy$ii-al prop-
erties (e*tx>ciiilly moss concentration)
would uid in the design of control cqnijj-
ment ami indicate cormspondoiicf be-
tween the various types of regulations
for particulate air pollutants. Often an
emission source will meet the paniculate
matter concentration requircint'tit but
not the visual standard (plume opacity;.
Previous Work
Correlations of particle nu-* concen-
tration to light trtinfmittitnce have been
ifjxirted for a few air pollution sources.
Stoecher1 and Hurley and Bailey1 re-
ported measurements of particulate
mas* concentration and opacity from
eon I combustion. Stern1 reported the
ItinKclmann number ex|>eeted for var-
ious fly ush concentrations from a rual
fired |>oivcr plant. sirniilt;nieo«i!« tneo-
suirrncnts of part irulate ma.-s con«-c.;tta-
tion and plume transmittanrc for white
and black (fuel oil) sinokp «nitrees weie
rc|>ortecl by Conner and Hmlkiit.*on.'
Gun>ler* reported smoke meter measure-
imiils of stack tr:in«nuttaii(T ami nui««
concentration for the cnii>M frntu a
Kraft reentry furnace. TlH*>o >tuilie»
iinlii akil that in .1 siii|tk> -..iirci' thv light
extinction of the jiartivlo is diwtly rr-
latnl tu the ]i;irtlfli% lnu>s < iviurutl;tlioii.
Scatter in the i>\|H>rinieiit:il dnta ran U-
attiilinteil in part to rhaiicis in tin*
pun irk site dittriliiition. 'i'lie inalttlity
to control the paiticli- >uo i(i>tri(mti,>n
was ei(ed hy KiiKikihl' atnl l»y Mitclu-ll
Journal of the Air Pollution Control Association
23
-------
Table I. Ufht extinction relationships of
plumes.
Fractional Equivalent
transmitted Rincelmann opacity
light number Per cent
l.O
0.8
0.6
0.4
0.2
0
0
1
z
3
4
5
0
20
40
60
BO
100
and Engdahl7 as a problem in developing
an empirical relationship.
The two general theoretical ap-
proaches have been (1) to assume a
monodis|)erse size distribution (or a
mean effective particle size) or (2) as-
ciime a mathematical relationship for a
|>olydi-|>*rsc size distribution. Huuks-
ley et «/.,' re[>orted relationships between
|iliune 1 115(1 1 extinction unit mass con-
centrutimi for an average monodisperse
-ize much smaller than the wavelength of
light :uul for an average monodisperse
size much larger than the wavelength of
light. (lux! agreement was reported
with (he duta of Stoecher for the small
l»artu-le case.' Conner and Hodkinson4
reported the use of a mean effective
|>artirle diameter to explain their duta
and presented calculation* relating mass
concentration to plume transmittance
for average particle sizes in bluck and
white nni>-iims. Rohin.soti* re|w>rted
the u-e of size distribution data for iron
foundry emissions to calculate nu-
merically the effect of control equipment
on the plume opacity. The Uuy Area
Pollution Control Hoard Regulation 2*
has a provision limiting the concentra-
tion from source* with a relationship
developed from a Uincrlmjinn No. 2.
Robin-Km reported that thi- regulation
was devi>li)|H*d assuming an oil aerosol
with a geometric mass mean radius of
O.J3M niti\ a KPonwtrir standard devia-
tion of 3.4. 1'iliit and Kn-or" prex-ntrd
general relationships of particubte mats
concentration to plume triin.«mittance
for log-normal particle size ilUtrihutKin.1
and Mack and while emissions.
Obj«ctlv«« of Thl« P«p«r
The objrc-tives of this pu|»er are: (I)
to extend the wiir-rul mathematical re-
lationship* Itftwoen plume opacity and
IwrticulatK air |x>llutunt properties as
reported by I'ilut and Kn-or to a wider
range of variables, (2) to indicate the
effect and ran ire of values of particle re-
fractive index and density, and (3) to
rrmilly rrconh-d siniiiltane«tu!«
t* ul the plume o|iucity und
Optical »V«o«r«o« of Partkulate Matter
Uf M Scattorhtf TMory
Tin- attenuation of a rnllimated bt-um
tit ttKht thruiiKh a turbid medium over
August 1971 Vokimt 21. No. I
a path length L 'a given by the Bouguer
law (Lambert-Deer law)
///• «• *xp| — bL\ (I)
where I/It a the fraction of transmitted
light and 6 is the extinction coefficient of
a volume of aerosol (in'1). Equation
(1), in a slightly different form, has also
been used to relate light transmit tunee
of particle suspensions in liquids. Skin-
ner and Boas-Traube" reported an equa-
tion in the form
-exp|-Spiri|
(2)
where Sp is the specific projected par-
ticle extinction area (m'/g) and H* is the
paniculate mass concentration (g/m1).
Skinner and Boas-Traub« verified equa-
tion (2) for a wide variety of conditions
for a transmittance range of about
SO-10%. Equations (1) and (2) do not
describe the effect of multifile tight
scattering which may be found in highly
concentrated suspensions or over long
path lengths. Hodkuison" reported
that multiple light scattering is rarely
important in extinction measurements
of aerosols.
The light extinction coefficient 6 is
well defined theoretically and can be
used to develop relationships for the
specific projected particle extinction
area Sp. The extinction coefficient for
a volume of aerosol coni|x>sed of spher-
ical particles is given by
6 - r I n(r)dr (4)
i
where p is the average particle density.
The particle size frequency distribution
n(r) is related to the total particle num.
ber concentration Ar and the panicle
number fraction frequency /(r) by
»(r) - tf/M (5)
The fraction of particles between r and
r + dr is obtained by multiplying/(r)
by the particle radius increment, dr.
Horvuth and Charlson" retried that
the ratio of paniculate mass concentra-
tion to the extinction coefficient \V/b is
useful for correlations of atmospheric
visibility data. The theoretical
ratio from equation (3) and (4) is
, ,•
/* -
4 r>
-fl
«» J r,
Qt(«,m)r*n(T)dr
The ratio can be made concentration
independent for single particle scattering
by substituting equation (5) into equa-
tion (6)
r'/(r)dr
f'
LJr.
CT)
For convenience, Pilot and Eitsor
(1970)" assigned the name parameter
K to the integral ratio in brackets
(specific particulatc volume, cm'/mV
extinction coefficient m~'). The pa-
rameter K is dimtrnsionully simitar to the
volume Mirface characteristic size de-
scribed by Herdan (I960).'* K is pri-
manly a function of the particle size
distribution, refractive index, and to a
less degree, the wavelength of light.
41?
24
-------
Table IL Selected *ir pollutant list distribution data.
Sou re*.
Uncontrolled
Wood smoke
Oil fired power
plant
Electric steel
furnace
Automobile tall
pipe
Cement dust
Pulverized coal
power plant
Hot mix asphalt
Spreader-stoker
coal furnace
Geometric mean
radius.
r«*iji
0.035
0.5
1.1
4.6
t.t
9.5
17
35
Geometric standard
deviation, r.
1.7
)
1.2
31
3
4
2
5
Reference
11
19
20
21
22
23
20
23
particle. For example, eentospherea
(hollow particles) with a density less
than I g/cc are sometimes found in
power plant emiMtions."
Calculations
The equation for parameter K it ob-
tained by substituting equation (11) for
the size frequency distribution /(r) into
the integral ratio in equation (7) re-
sulting in
K -
From equations (1) and (2), the ex-
tinction coefficient b is related to the
specific projected area Sp and particle
mass concentration by
6 - SpW
(8)
By substituting equation (7) into equa-
tion (8), the speciSc projected area is
given by
(9)
A working equation can be developed
from equations (2) and (9) to calculate
the expected mass concentration for
various values of plume transmittance
(or opacity), average particle density,
and plume diameter
W - -A' I in (///,) (10)
Range ef Important Variables
Partick Sue Distribution. The log-
normal particle size distribution model
can be used to describe a wide variety
of polydispersed systems such as those
resulting from comminution of solids or
spraying of liquids. A complete de-
scription of the use of the log-normal
size distribution is given by Herdan"
and by Smith and Jordan." The tog-
normal size distribution for a number
frequency distribution is given by
exp-
in' r/r.,
(11)
where rn is the geometric numlwr mean
particle radius utid f, is the geometric
standard deviation (a measure of the
polydispersity or breadth of the particle
sire distribution). Lou-normal distri-
butions of particle tmmlxT, area, and
mass arc related mathematically. The
geometric standard deviation remains
the same for these tii>tril>utions. The
relationship between geometric number
and mass mean radii, r,.and r,^ respec-
tively is
lnrw - lnr>.- 31i»V, (12)
Size distribution data can be reduced
graphically by plotting ".smaller than"
cumulative size frequency versus size
on logarithmic probability paper, r,.,
for mass distribution data, U the radius
at the 50% size and t, is given by
84.13% sire 50% size
50% size 15.87% size
Particle size distributions reported for
air pollutants indicate that both the
geometric mass mean radius and the
geometric standard deviation can vary
over wide ranges. The particle size
distribution in the emissions from a
given source depends on the nature of
the source (combustion, metallurgical,
etc.), and the degree of collection.
Hopefully, similar source* should have
similar particle size distributions. A
summary of typical size distributions is
presented in Table II. The extremes
in the geometric mass mean radius were
from 0.04*. for wood smoke to 35M for
fly ash from an uncontrolled coal stoker.
The extremes in the geometric standard
deviation are 1.0 (monodisperse) to 31
reported for automobile emissions.
Refractiit Index. The optical pro|>-
erties of the particles are dcscritad by
the refractive index. The refractive
index is a complex number, m - n, - t'n:.
The real part, n\, describes the light
scattering pro|x-rtic-s and the imaginary
part, a,, describes the light absorption
of the particle material. In Table III
refractive indices for pure crystalline
solids und various liquids are presented.
Air ixillut tnt particles may l«com)iou pre.«cntcd in Table
III. For actual |*>liutanis the particle
der»ity may be much smaller than ex-
(x-cted from the pun- aulistunce due to
unhonioRt'ticou* composition of the
I r.
I rQ>
Jr>
(a,w)exp
The ]Miramctcr K wa* calculated using
equation (13) with equation (12) to ob-
tain r,. from r,,. Tlie efficiency factor
Qi(a,m) was calculated by forward
recursion met hod* and was in agreement
with the results reported by Pcnndorf.*
Equation (13) was integrated with the
trapezoidal rule, reported by Deirmend-
jian* to be suitable for integrations of
light scattering functions over particle
size. The value of Ar was about 1% of
r over the wide range of particle sizes.
The theoretical limit Qt - 2.0 was used
for values of a greater than 75. This is
a good assumption if the acceptance
angle of the instrument used to measure
light extinction is very small (for ex-
ample, the aci-cptuncc angle should be
less than 0.7° if the largest particle in the
duct is 5 jjm in diameter").
Results
Calculation of A' versus r,r and »i
The results for refractive indices of
1.33, 1.50, 1.96-0.661, and 2.S-0.02tar»
presented in Figures 1-4 respectively.
These results, as indicated in Table11*1,
cover the range of refractive index which
should be important. The refractive
index 2.8-0.02i is a value assumed to
represent a material such as iron oxide
with a weak light absorbing component.
A wavelength of light of 5oO nm was
used a* an average for visible light. It
i* approximately the- wavelength of
maximum sensitivity for the human eye.
The range of r,, and 9, is O.Ot to 100^
nnd 1.0 {monodi^icT.-e) to 10.0, resix-c-
lively, and .-hould incliule tin* values
ex|iertt%il for nio>t air |Milhit:tnt*.
The effect of refractive index i.< rel-
atively unimportant for particle railii
greater than ;il>mit O..V However, for
jturticlc railii Jr., than abmit ().;>*, the
nuiKiiitudcof tin-al>-i.il>inj: index (n>) is
very imimrtant. The light extinction
by pun- lii;lil Mallrniii: particle* (no
I III tit ubxirption n, - 0.0) drcrc:i.c»
25
Journal of the Air Pollution Control Association
-------
Table III. Physical properties ol pottlMe sir pollutanta,
rnpiilly with u decreu'p wtth ti\e \\*t of e<|ua-
liun <9) nnd the a»iiinmi> of an average
particle dniMly. A" run uUo Iw drier-
mtneil with kriuwledm* of the site dis-
tribution parameter.* i geometric ma*s
mron rndiu* r,. and the geometric
standard ili'viation -
*rtw* «>f the aernsol. OljvmiKly, ivhrn
thfn« »rp !;iri»e t:-M'iiiiiiil *in- ilotritnition
nui'li'l ivr ;i i-haiiKi* in the urnt-nl fii Ix'tM con
tin* '"itlM'iM »f purl nli- -i
nrnl tln> phine nparitv li
ili'vi iii'ins (itiiii the tln'ou'tii al prc
liwn- ma v rr«ult. "i'lir niiMiiirml K
in 'l.il'l'* l\* ni'lii'iile^ tlii> imiKiulnile of
thr n|i(i4-al :u'tmty (henry -hiHilil lie
«>iiMida ZnO
Wood (mode
Sulfunc acid
90%
Banian*.
C,H,
n-Decane
Water
Density,
g/cc
1.5
1.8-2.1
5.2
2.7
2.J2-2.M
2.7
5.6
1.1
1.811
O.M
0.71
1.0
Wave-
Tempara- length of
tura. light.
'C nm
— 589.]
- 436
546
623
- 519.1
— 589.3
— 589.)
- 589.3
- 589.3
— 540
18. r 589.3
20* 589.3
20* 589.1
20* 589.3
Refractive Index.
r
n.
1.77
1.90
1.96
2.00
2.78-3
1.5-1.1
1.544
1.47
2.0
1.53
1.437
1.501
1.412
1.133
n « m — n,i
"i
to~*
0.68
O.M
0.66
.01 1
Mf
f
Vary small
r
r
0.00095
Vary small
Vary am«N
Vary smalt
Vary imill
Ref-
erance
24
29
M
M
2f
N
M
27
M
M
M
M
Table W. Measured optical propettls* of emissions.
Source
Orchard heater
(Black smoke)
Coal power plant
(Fly ash)
Coal itokar
(BUck «moka)
Coal itokar
(Black imoka)
Oil power plant
(BUck smoka)
Whita smoke
Generator
W - 0.!2 g/m'
W-0.«g/m»
W. 1.00 g/m'
Kraft mill recovery
furnaca W «
0.15 g/m'
Venaer dryer
Li.)
0.4J
1.14
0.30
0.15
0.2
0.2
1.S2
1
Instrument
Visual
Bolometer
Smoka mater
Smoke mater
Smoka matar
Smoke mater
Bolomatar
Visual
i
Average
Sp m'/g
20
0.78
6.1
4.6
8.7
2.5
1.8
5.75
1.7
2.8
(as- Avarag*
sumad) K cm'/m*
2.0 0.025
2.0 0.64
1.95 0.084
1.95 0.11
1.95 0.059
0.87
0.46
0.10
0.20
1.0 0.6
1.0 0.36
Haf-
erance
10
author
1
2
4
4
11
12.11
part tries" yr cloud* of spherical |wr-
tirli".14 Liitht e.xtinrtirm by non-«plier-
iral partirU-t in randrun motion wn* re-
(Hirted by l|iNlkiti«in" to IN- nrnrly tin-
«uit\e a* thai fur xphfriral pui tii li>J
much lnrit'T and nitn-h minllrr thun the
wavplencth of incident linht. The effect
of irrri(iilnr particles nith sili'< nr;ir (be
wnvclvintl\ of h|(ht !•» to ^mU for nmnv yr»r<." The li(ht
tnltering eorllirient of ft eloud of |wr-
ticli-s nas r«'|H>rtei| hy Mnlland, flat.*
for tiilr dust and by ZUPV, ft at ," for
ortifit ml f 4.) Rite distribution* u
rtwim in FIKUIV* l-t. Aitiiitioually,
(he avernni1 (mrticle den!«it\ and the re.
Au«u*t
)\. No. I
26
-------
\Geomatnc itandard deviation.
ft
Rttrxtivt inde«-l 13
w«v« length of I'jtit *J50 f»m
10 T 10 ' 10° 10' 10*
Geometric mis* mean radiui,r,. (micron*)
1. Parameter K at a function of the
log-normal «i» dittrlbution parameter* for
liquid water.
Tractive index (the magnitude of the
imaginary part is very important for
small particles) may not be accurately
known for a given source.
Simple Calculation
The estimation of the maximum
allowable participate mass concentra-
tion for a given plume opacity standard
will be illustrated by an example cal-
culation. Let us u-vumc that the regu-
lation s|>ecifies a maximum allowable
plume opacity of Ringelmann No. 1
(&09o light transmittance through the
plume). It is given that the stack
diameter L is 32.S ft (10 m). the exhaust
gases are at 300°F, and the particle
properties are a mass mean radius r,» of
2>i, a geometric standard deviation a,
of 3, a density p of 2 K 'cm1, :md a
refractive index m of 1 .90-0. 6fii (carbon).
From Figure 3, a K of 0.6 cm1, m1 is
obtained. With equation HO) the
particle mass concentration which cor-
responds to the Ringelmann No. 1 is
calculated
If/
10
to
10
Geometne ttandard devwtion.
R«ir*ctiveindnul.9« U.Mi!
Wive lenfth ol Ii|hl*ii0 nm|
10*10 l 10" 10' 1C1
CtomilrK nwu mem radiut. f^ (micronu
Fl(ur* I. Parameter K aa a (unction of th*
loc-normal tit* distribution parameters for •
black aerosol.
10'' 10 ' 10U 10' 10*
Geometric mm mcin rtdiui, r,. (micrant)
Flfure t. Parameter Kit* (unction of the
lOaVnormil me distfibulion parameters for •
while aerosol.
-(0.6cmVm1)(2K/cmt) InO.S
10m
ir - 0.027 g/cm' at stack conditions
Converting to units of gr, ft1 at SOOT
IP - 0.027 I'm-
Converting to standard conditions at
60°F
Therefore for this case the maximum
allowable particular mats concentra-
tion which fonvsponds to a Riii^clmatui
No. 1 i> 0.012 cr, ACT or 0.01S vx SCF.
It shoulil Ix* notc*uin[>tiuu of
constant K. Actually there may be
some chaiiKi* in K u]iou the in.siullation
of particle cullcction equipment >lue to
the decrease in the particle sin-. This
variation can be. taken into account if
information concerning the pnriii-le site
JO*
10'
10
Refractive mde«"iSO
HM-MO nm
10- •' 10-
Gnomelric ni
10"
ID'
io»
Ft«ura «, Parameter K at a (unction of the)
hypothetical refractive index for iron oaide.
too
Journal of the Air Pollution Control Allocution
27
-------
dii.trilwt.ion of the controlled emission U
available (may be predicted either from
particle size measurement* at similar
source* or by calculations usin$ particle
collection efficiencies of control equip-
ment as a function of particle size).
Conclusions
A gfiieral tlieoretic:i I relationship I*-
tween plume opacity and particle prop-
ertie< ha* Iwen developed and compared
\vitli ex|M>rimentul data. Numerical re-
sult« have l>ccn presented to include the
ramie* of physical pro|>rrties expected
for air |M>ltutant*. The parameter K U
primarily a function of particle sue for
particle radii greater than about 0.5 urn
and primarily a function of refractive
index fur smaller particles'. Plume
opacity can be estimated for given
source-. I'nmi the numerical re-ult*.
Acknowledgments
The it-search was supported by the
United State* Public Health Service,
National Air Pollution Control Ad-
nuni'tratioii Training Grant AP 29.
The assistance of Professor August T.
Ro«ano, Rick A. Kestor, \Y'e$ Snowden,
John C. llox-h, and George Beckwith;
and dis.cussioti.i with Gene W. Smith,
Jon Peacy, Dr. Robert J. Charlson,
Steinar Lar.-M-n, and Leslie E. Sparks
are (Hatefully acknowledged. The loan
of u Miioki* meter u. i* appreciated.
References
I. Stern, A. C.. Air Pollution Vol. Ill,
•JmJ oil.. A. C. Stern, lid., Academic
Prev. New York. Chap 31. 196*.
2. Mowker, \V. F.. "Smoke density
measurement," Aleck. Eng. 72, 793
(ItWOl.
3. Hurley, T. F. and Bailey, P. L., "The
correlation of optical deiiMfy with the
cimceniration and composition of the
sm.'ke finitted from a Lancashire
Holler," J. ln*t. purtil, W4 (19.58).
4. Conner, U. U. and Hodkiruon, J. U.,
Optical I'roprrtiei unit I'l'iuaJ Elfectl
of Smoke-Shirk riitmei, I'.H.rf. Publ.
No. WJ-AP-:;mi!MJ7).
5. <.::in.«ler, N. II., "The Use of a Bo-
lometer for Continuous Measurement
of Paniculate Losses from Kraft
Mill Recovery Furnaces," Pacific
Northwest International Section. Air
Poll. Control Aisoc., Vancouver, B. C.
'Nov. I'.MW).
6. EtiKdahl, It. B., "Correlation* of
juiliiU ronient in ga«," Meek. tng.
73, -'4:1 (I»5I).
August 1971 Volum* 21. No. I
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
Mitchell, R. I. and EngdmhJ, R. B.,
"A survey for improved method* for
the meuurement of particulate con-
centration in flowing gin streams,"
/. Air Pill Control Attot. 13, 9 (1963).
Hawksley, P. U., Badzioch, S. and
Blackett, J., Mtasurtment of Solids
in Flue (jatet, British Coal Utilization
Re*. Assoc. Leatherhead, England,
1901.
Robinson, E., "The effects of air
pollution on visibility," Air Pollution
Vol. I A. C. Stern", Ed., Academic
Pres*, New York, Chap 7, 1962.
Bay Area Pollution Control Board
Regulation 2, HMJ Minion St., San
FrancL-co. Calif. (11(02).
Pilot. M. J. and Ensor, D. S., "Plume
opacity and paniculate ma&> con-
centration,'1 Atmot. Environ. 4, 163
(1970).
Skinner. O. G. and Boo*-Trabe, 5..
"The Ii(tht extinction method of
particle sue estimation," Insl. Ckem.
Engrt.23,57 (1947).
Hodkinson, J. U., "The optical mea-
surement of aero>ol.s," Arronol Seitnet,
C. X. Davies, Ed. Academic Press,
New York. Chap 10. l'J(J45.
van de Hulst. H.C. Light StaUt ring by
Small f'ariiclet, John Wiley 4 SUM,
Inc., New York, I'J.57.
Hnrvath, H. and CharL-ton, R. J.,
"The direct optical measurement of
atmospheric air pollution." Amer.
Iml. Hi,g. An. J., 30. 500 (19691.
H«rdan. (•.. Small 1'nrltcle Statittiei,
Biitterworths. London. I'JOO.
.Smith. J. E. ami Jordan, M. L.,
"MathematicaJ and graphical inter-
pretation of the log-normal law for
partirle gize dUtrib>iti»n analysis,"
J. Colloid AVi. 19, A-l'J (1964).
Fo.-.(er, \V. W., "The .->iie of wood
amoke particles," Arrvlynnmic Cap-
ture af I'.irttclta, K. (.;. IlicharU.-on,
Ed. Periamon PreMJ, New York,
. . .
Smith, U'. S.. Atmo.iphrric EIHIMHUU
frUrn Fuel Oil Cdmbtulion, P.II.S.
Publ. No. fCjy-AP-2 (I9«i2).
Air Pollution Enijinrrring .\fnniial.
P.H.S. Publ. No. 9«.»9-AP-«0 (I907).
Habit-i,
, K., "Characterization of
particulate lead in vehicle exhaust-
exrwrimental terhniepies," A.C:S.
Symp. on Air Quality and Lead.
Minneapolis, Minn. (April 19C9).
Kreichclf. T. E.. Kemnitz. D. A., and
Culle, S. T.. AtmoxpHeric Emittioni
from Uif Ufamtifarture of Portland
Cemrnt. P.H.S. Publ. No. 999-AP-I7
/ I 'III** ^
Smith, \V. S. and Gruber, C. W.
Atmospheric Emittiont from Coal
Comhuition. An Inventory (luiJe,
P.H.rf. Publ. No. 9V.I-AP-24 (1966).
Pla», U. N., "Mie scattering and
absorption cross sections for alum-
inum oxide and magnesium oxide,"
Appl. Optit» 3, S67 (1904).
StelTens, C., "Viability and air pc.l-
lulion," Air Pollution Handbook Magill,
P. L.. Holden, F. R. and Ackley, C.,
!-M* McGraw-Hill, New York, sec-
tion 6, 1956.
26. Hodgman, C. D., Ed., Handbook of
Chtmutru and Phyiict, 40th ed.
Chemical Rubber Co., Cleveland.
1939.
27. Foster, W. W., "Attenuation of light
by wood smoke," Brit. J. Appt.
Pkyi. 10, 416 M959).
28. Penndorf, R. B., "New tables of total
Mie scattering coefficients for spherical
particles of real refractive indexes
(1.33 to 1.50)," J. Opt. Soe. Amer. 47,
1010 (1957).
29. Deirmendjian, D., Electromagnetic
Scattering on Spherical Polyditpenioiu
American Elsevier Publ. Co. New
York, 1969, p. S9.
30. Snowden, W. D., Valentine, Fisher
and Tomlinson, Inc. Seattle, Wash.,
Personal Communication (1970).
31. Bo-rh, J. C., "Size Distributions of
Aerosols Emitted from a Kraft Mill
Recovery Furnace," M.S. Thesis,
Chem. Eng. University of Wash..
Seattle (1909).
32. Lars.sen, S., Ensor, D. S., Sparks.
L. E. and Pilat, M. J., "Size Dis-
tribution of Aerosols Emitted from a
Veneer Dryer," Presented at Pacific
Northwest International Section, Air
Poll. Control Assoc., Spokane, Wash.
33. Bcckwith. G., Puget Sound Air Pollu-
tion Control Agency, Seattle, Wash.
Personal Communication (Jan., 1970)
34. Blau. H. H., Jr.. McClee«!,.D. J. tod
\Vut.son, D. "Scattering by individual
transparent spheres," Appl. Optict 9
25£> (1970).
35. Holland, A. C. and Draper, J. S., "An-
alytical and experimental investiga-
tion of light scattering from poly-
di.npersion* of Mie particles," Appl
Optic* o, 511 O'J67).
36. Zuev, V. E., Kosh.'lev, B. P., Tvoro-
gov, S. I), and Khmelcut), (Trans.
bv l». A. K.-eliii).
Mr. Ensor and Dr. Pilat, Asso-
ciate Professor of Air Resources)
Engineering, are in the Water and
Air Resources Diy., Department
of Civil Engineering, Univer.titv
of Washington, Seattle. Thu
paper was presented as Paper
No. 70J%:i at the 63rd Annual Mwt-
ing of the Air Pollution Control
Association, June 1970.
SOI
28
-------
Reprinted from AFCA Journal, Vol. 23, No. 7, July 1973
IGCI Reports Consensus on Industrial Emission Levels
Producing "C/ear" or "Near Clear" Stacks
\ survey of the motiilirr companies
of tlic Il\(lii>tri:il (!;IH ('It'Miiiiiv: In-
htltuto (KiC'I) ha* developed tin' follow-
ing fon-cii5U-> as to pmi.-sioii levels which
ccnernlly produce or result in clear or
near clc.tr stacks for various industrial
applications.*
Understandably, re|>orts IGCI. there
are numerous <|ii:ilifications as to the
Mi-curacy of the data under all eircum-
>tances. The reader is therefore cau-
tioned to rounder any special factors
applicable to hi.i own operational con-
ditions in using these quideiine*.
The data are for general informational
use to those concerned with the appli-
cation of air |>ollutioii control equip-
ment. Neither the IGCI nor any
of its members make any representation
a* to the Accuracy of the data as A\t-
plied to any specific installation.
Variables sui-h a> path length, angle
of incidence of liiiht, moisture content
of effluent, weather condition!*, and
proi-e.-s changes may .-i^nincantly change
stack appearance irrespective of the
wtijjht of paniculate emivion.
User* and manufacturer* of air \m\\H-
tion control equipment arc tilled to
submit data to IGCI relating to their
own experience* with emission levels
which result in clear or near clear stacks.
Confirming or contradictory data, or
comment.-, in general will be welcomed
by the Industrial Gas Cleaning In-
stitute, 1116 Summer Street, P.O. liox
1333, Stamford, Conn. 00004.
* A paper wax prison led at the May
IK, I'.i'.'i, meeting in lialtimore of the
South Atlaniic Suite* Action of A PC A
prepare
llii- cim-cn-u- data. Tlic paper »'ua
presented by I'.nqcne 1*. SluMiiy, manager,
I'linlncl riuiKiini; nnd Dcvcl'ipincnt,
l.nviii'iiiiinil:il Sy-luiiiN Uiv., Kopprr*
('ninpiiiiv, hie. and ctmriitly vice prrv
iilciii, IdC'I. Tin-«-ni in- PUJKT will iip|war
in the mcvlih;{ i>im-iitlim;«.
Industrial process emission levels generally cipeeted to produce visually clear
(or near clear) stacks, eiccpting condensed moisture plume.
Electrostatic precioitators.
fabric filters.
Industrial process Grams/ACF at stack txit
classification gas temperaturo. *F
Utilitiesaod industrial
power plant fuel-fired
boilers
Coal-pulverized
Coal-cyclone
Coal- stoker
Oil
Wood and bark
Bagasse
Fluid cok«
Pulp and paper
Kraft recovery
Boiler
Soda recovery
Boiler
Lime sludge kiln
Rock products (Kiln«)
Cement— Dry
Wat
Gypsum
AJumma
Lime
Bauxite
Mag. oxide
Steel
Basic oxygen
Furnace
Open hearth
Electric furnace
Sintering
Ore roasters
Cupola
Pyrites roaster
Taconite roaster
Hot scarfing
Mining and metallurgical
(Non-ferrous)
Zinc roaster (Ore)
Zinc smelter (Malting)
Copper roaster
Copper reverberatory
furnace
Coon«r converter
Aluminum— Hall process
Soderberg process
llmenite dryer
TiO: process
Molybdenum roaster
Ore beneficiation
Miscellaneous
Refinery catalyst
regenerator
Municipal incinerators
Apartment incinerators
Spray drying
Precious metal refininf
0.020 300
0.010 (A 300
0.010 <" 300
0.020 fe400
o.ois a 47;
0.015 ft 500
0.02 (•• 350
0.01 (.1 400
0.01 '" 400
Estimated
humidity*
Vol. %.
H:O
t
5
5
6
10
10
Dry
30
30
30
3
25
25
•20
1
3
20
20
1
S
10
10
20
10
10
25-40
9
%
S
S
S
S
25
2$
5
S
5
15-20
20
20
25
S
Wet scrubbers.
Grams/SCF Dry*
(SCF <& 70*F and
14.7 Psia)
0.029-0.031
0.014-O.Olt
0.030-0.090
0.0047-0.0053
0.090
0.072
O.C2Z-0.02*
0.040-0.043
0.040-0.043
0.046
0.026-0.030
0.034-0.040
0.048
0.040
0.039-0.050
0.035-0.037
0.024
0.021
O.C23-O.M7
0.026-0.032
0.040
0.036-0.040
0.029-0.03*
0.036-0.040
0.032
0.019-0.025
0.011
0.017
0.019
0.030
0.019
0.075
0.003
0.03*
0.015
0.015
0.034
0.032
0.034
0.038
0.022
0.0'. 7
' Based on etdmjted water vaoor content ol hot t[«ies
-------
Measurement of Opacity and Particulate
Emissions with an On-Stack Transmissometer
ttolnz P. Beutncr
LearSiegler, I no, Environmental Technology Division
An on-stock transmissometer system which is designed to
provide o precision meosurement of the opocity of visible
emissions is described. The sources of error in opacity
measurements with regard to recent EPA emission monitor-
ing requirements and planned specifications are discussed.
Sources of error are voltage changes, temperature changes,
light source and detector aging and effects of ambient
light. Other major operational errors are caused by
alignment drift and soiling drift. The methods employed to
minimize these errors achieve an accuracy of ±3% of
span and a maintenance free operational period of 3
months. The relationships between optical density, opacity
and transmittance are described. The instrument measure-
ment can be correlated with dust loading provided the
particle size distribution is constant. Examples are given
of correlations obtained between optical density and por-
ticulate concentration in the gas on various types of emis-
sion sources and the observed error margins are sum-
marized.
TrMKtlMr Unit
Flflura 1. Typical RM4 arrangement on a stack.
Two standard methods for the continuous measurement of
pnrticulatc emissions are:
Determination of the Ringelmann number or the equiv-
alent opacity of visible emissions.
Manual .sampling using particulutc sampling trains.
The problems of judging visual emission* by human observer*
are well known. The original Kingclmann scale, comparing
the shade of gray of smoke with that of u chart, w useful only
for black smoke emission*. TIM lay, smoke readers are trained
to judge 'the equivalent opacity of emissions of any color.
However, tlic result* are eiiorious manual procedure which, in large stacks, may
require 2 to 4 man-weeks of effort involving u cost of from
$3000 to $10,000. Typically, such sampling is performed
annually or hiamumlly, and as a result, it dix-s not provide in-
formation iilioiit the porforinam-e of control equipment during
the interval Ix'hvreii incMsiircmcnl.*.
««7>">"'-d/romAPCA JOURNAL, Vol «, No 9, .SYptvmbcr IH74
31
-------
Flfura 2. RM4 trsn*ml«som«t»r optical system.
Clearly, a better method for measuring and continuously
monitoring participate emissions is needed. This paper dis-
cusses an on-stack optical transmissometer system for pre-
cision measurement of the opacity of emissions and correlation
with the particulate concentration in the gus. The R.M4
Visible Emission Monitoring System was designed and de-
velo|x.ld in Germany and complies with the very strict long
term operational i>crformance s|x>cincations established by
the German pollution regulatory agency for continuous partic-
ulate monitoring instruments. It also meets the require-
ments of the United States Knvironmental Protection Agency
(EPA) for opacity measuring instruments. There arc over
1000 of these instruments now o|x>rating in Euro)*1 and the
United States. The instrument* are marketed and produced
in the United States, under license, by the Environmental
Technology Division of LearSiegler, Inc.
Transmissometer System Description
Figure 1 illustrates a generalised installation of the instru-
ment system, excluding the readout unit in the control room.
This instrument consists of an optical transmitter, receiver
(transceiver) unit which is attached to one side of the duct or
stack, and a similar housing for the retroreflector on the other
side.
The transceiver contains a light source, a photocell/detec-
tor, and electronic signal-processing circuitry. The passive
reflector unit require* no electrical connections except for the
air blower provided for air (lushing on that side.
Itoth the transceiver ami the reflector are eqnip|M>d with
socially constructed air flow attachments to keep the optical
windows free of dirt de|H>sits. The purge air normally is
supplied by two high-volume nir blowers with filters. They
provide up to NO cfm each, depending on pressure conditions
within the stack and pressure drop through the filter. The
air-purging system typically provides 3 to (i months of main-
tenance-free o|>craticd, dual-beam, optical
system (Figure 2). This design automatically com|>ensatcs
fiir the HTi'ds of tcm|H-ruturi' changes, voltage changes, and
component aging. The instrument is non:nis|x»nsive to am-
bient light, since only pulsed light at cither W the two chop|ied
frequencies is measured.
Light from a single source in the transceiver is divided into
a measuring Ix-am and a reference beam. The measuring
beam is trmiHiiilted across tin- entire width of the smoke
NC 32
channel to a corner-cube retrorefleetor which directs the beam
back through the smoke channel to the photocell detector, re-
gardless of small alignment variations between the two units.
The reference beam is projected directly onto the same photo-
cell detector. A rotating disc modulates the two light beams
at different frequencies so that both beams can be measured
by a common photocell, and electronic circuitry then .com-
pares the signals generated by the two beams. The reference
beam provides automatic gain control and, therefore, com-
|>cnsates for any chiingc in light output or photocell rcs|>onae
as a result of tomi>eraturc variations, voltage fluctuations,
or component aging. As a result, the instrument is free of
drift errors usually caused by these variables.
Tolerance for Misalignment
Another common source of error in smoke measuring in-
stallations is a variation in alignment as a result of buckling
and teni|>eraturc movements of the stack or duct walla to
which the instrument is attached. As a result, some instru-
ments require the installation of a slotted pipe across the duct
or stick to maintain rigid alignment. Among the disadvan-
tages of this arrangement arc the ]>o*sibility of measuring a
non-representative sample of the smoke or dust, a reduced
instrument sensitivity as a result of measuring only the
smoke passing through the slotted section of the pi|>e, and the
IKissibility of light vignetting, i.e., scattered light is reflected
off the walls ami reaches the detector. In large installations
and at high o|x>rating tcm|>eratures, such a pijx? can nag,
causing a large measurement error, and the pipe usually is not
recommended for stuck widths greater than 20 ft. The RM4
instrument system does not utilize a pi|>e across the smoke
channel, and it can be used over distances as great as 52 ft.
The instrument system tolerates commonly encountered
alignment changes up to ±0.4°, without loss in accuracy, by
utilizing a simple patented concept.1' The light beam is
focused on the retrorellector for each s|>ecinc distance and luw
a uniform intensity (±2%) throughout its cross section at the
focal distance. For each x|H»cific distance, a reflector a|>cr-
ture size is chosen that will maintain a large ratio of beam
cross sectional area to reflector area. Since the beam is uni-
form, the retrorefleetor always returns a constant amount of
light, regardless of what |mrtion of the beam impinges U|*m
the retrorefleetor. Furthermore, the corner cube retrore-
llector always returns light directly to the source, regardless of
the angl*' <>f incidence. Within its accuracy specifications,
this instrument system tolerates alignment changes of ±0.4°'
which is equivalent to mcasuring-l>cam movements of 1 to 3
in. at distance* of 10 and .'W ft. This is sufficient to account
for all alignment variations encountered in actual practice.
In addition, the instrument is cquip|x-d with an optical bull's
eye which allows verification of the alignment at any time
during o|>cration. If necessary, the alignment can be ad-
justed using two fine-adjustment screws on the instrument.
Automatic Calibration
Temperature changes, voltage changes, accumulation of dirt
on the optical windows, and alignment changes urc the major
sources of drift in smoke or dust density measuring installa-
tions; the calibration of such installations must be checked
frequently. New source |x>rformancc standards, published
by the KPA,1 require o|«icity monitoring instrumentation in
all new steam electric power generating stations and further
.sjHH'ify that such instruments be calibrated at least once every
»lay. None of the two-ended smoke-density monitoring in-
strument* so far available can be calibrated during <>i>cration
on the stiflrk since, in any two-ended system (light source
and detector on op|xisite sides of the smoke channel), it is
necessary to stop the exhaust gas flow in order to obtain a
Journal of the Air Pollution Control Association
-------
calibration for awro pereent opacity. Tke angle-ended RM4
system checks its iero and span calibration automatically at
regular intervals without interrupting stack operation. The
calibration values obtained are recorded directly on the chart
paper. The calibration checks can also be activated man-
ually at any time from the control room.
The calibration checks in the system are accomplished by
inserting, in the light path outside of the optical window of the
transceiver, a zero reflector which simulates the retroreflector
on the opposite side of the smoke channel. A variable dia-
phragm on the zero calibration reflector is adjusted during
instrument setup so that as much light is returned to the
photocell by the calibration reflector as the retrorollector on
the opposite side of the smoke would return under a "clear-
stack" condition. Span calibration is accomplished by in-
serting a neutral density filter of known opacity value into
the reflected zero beam. The value of the selected span cali-
bration point depends upon the particular measurement range
selected for a specific installation. The rero calibration
check indicates any drift in the instrument measuring circuit
and measures any loss of light transmission through the op-
tical window as a result of dust accumulation. A deviation
from zero nlerts the operator in the control room when clean-
ing of the optical windows is required. The loss of light as a
result of dirt accumulation on the reflector side of the instru-
ment system can normally be assumed to equal that on the in-
strument side, since both sides are protected by identical air
purging systems and arc subject to essentially the same stack-
gas flow and pressure conditions.
An example of a smoke trace is shown in Figure 3. The
zero and span calibration values are recorded automatically
at selectable, periodic intervals. Figure 3 also shows periodic
emission spikes, resulting from the rapping of different precip-
itator sections. Therefore, the instrument is a very effective
tool for monitoring the ixrformancc of each precipitator sec-
tion and for detecting malfunctions in precipitator operation.
Accuracy end Sensitivity
As a result of the design features described, the instrument
system achieves an operational accuracy of better than ±3%
of span or ±1.5% opacity, whichever is greater, over an
operational period of at least three months. Test data ob-
tained in Germany as part of an acceptance test performed by
the Technischer tjberwachungs-Vercin (TOY),' demonstrate
that none of the following variables causes an error exceeding
±3% of span for a full scale range of 0 to 0.45 double-pass
optical density* (0 to 0.225 single pass or 0 to 40.4% opacity),
and most are well under this limit:
Voltage variations within ± 10% of nominal.
Temperature variations from -30°C to + S5'C (-22°F
to+13l°F).
Component aging and effects of ambient light.
Alignment variations within ±0.4° of the optical axis.
Calibration and linearity errors in measurement scale.
Operational tests on stack emissions of cement plants and
power plants confirm that none of the following errors exceeds
±3% of span for the 0 to 0.45 double-pass optical density
full-scale range:
Zero and .spun drift over a maintenance-free operational
period of 3 mo.
Soiling and alignment drift over & maintenance-free O|xra-
tinnal IKTKK] of 3 mo.
• The iiutnimenfe light beam pae*ee through the emoke t*lee. therefore
neacurM more than the opwtily eeea by aa obeerver (eee further below).
Figure 1. Example of emission trace from cement plant showing
hourly zero and span calibration checks.
A choice of five full-scale measuring ranges which correspond
to stack opacities of 0 to 9.8%, 0 to 18.7%, 0 to 40.4%, 0 to
64.5%, and 0 to 87.4% is provided. The instrument is sensi-
tive to changes as low aa 0.05% opacity, and, on its lowest
range, it can accurately measure opacities of 1 to 2%. This
high sensitivity is a result both of the double pass of the light
through the entire stuck or duct width and of the expanded
measuring scales.
The absolute accuracy of the transmissometer is baaed on
the calibration of the linear scale of optical density against
neutral density niters of known transmittance. The mea-
sured values must be within ±2% of the calibrated values of
the niters.
The calibration against neutral density filters is acceptable
if the angles of projection and view are small. A neutral den-
sity filter is not strictly equivalent to a smoke or dust aerosol,
since light attenuation in the filter is due primarily to absorp-
tion, while attenuation in the aerosol is the result of both ab-
sorption and scattering. Instruments with large angles of
view measure a jwrtion of the forward (or backward) scat-
tered light and therefore measure a lower apparent opacity
for the aerosol than for a neutral density filter of equal o]iao-
ity.*>' Since, for particle sizes under 2 microns, nearly an
order of magnitude less tight is backscattcred than forward
scattered, and since the angles of view arid projection are
very small, the folded beam system utilized in the trans-
missometer has an absolute accuracy equal to any equivalent
two-ended transmissometer. The angle of view for this in-
strument is ± 1.8° and the angle of projection is ±0.7° from
the optical axis. Proposed E FA specifications for visible emis-
sion measuring instruments suggest limits of ±2.5° for the
angles of view and projection in order to assure an accurate
absolute oimcity measurement by instruments from different
manufacturers.
Photopfc Light
An additional requirement for absolute accuracy of the
measurement is a specified spectral range, since light attenua-
tion by a polydisncne aerosol with mean particle size of less
than I it \s a function of the wavelength of the light. The
specified spectral distribution is pkotopic, the same as that of
the Unlit-adapted human eye, because one objective is the
measurement of the opacity of visible emissions as observed
by the human eye.
The instrument utilizes a photocell/filter combination to
achieve "photopie" H[X'etral sensitivity. Figure 4 shows the
8|>ectrul sensitivity of the instrument compared to the output
of an incandescent light source. The maximum light in-
tensity is at 0.55 micron wavelength compared to about 1.0
micron for the- incandescent source. Instruments sensitive to
the entire output of the light source arc subject to two serious
September 1974 Volume 24, No. 9
33
K7
-------
100
2.f
Retire 4. Photopic spectral sensitivity of the RM4 compared
to Incandescent light spectrum.
errors. First, water absorption bands in the near infrared
portion of the s|>ectrum cause large measurement errors for
•tack gases containing high humidity. Second, the instru-
ment response to submicron participate matter is significantly
lower than the re.s|>onsc of the human eye, resulting in low
readings when the stuck emissions contain substantial portions
of submicron particulutc matter.
Figure 5 shows the light attenuation of a |x>lydis|>erse aero-
sol for two different spectral maxima as a function of the mean
particle size.7 The attenuation of the 1.0 M light falls off
significantly at about 0.8 to 0.6 n particle size, while the 0.55
M light is attenuated by particulate matter down to 0.3 to
0.2^.size.
In the absence of photopic light and es|>cciully when the
major instrument resjwnse is within the infrared region, as in
instruments utilizing a bolometer detector cell, large errors
result when the emissions contain large portions of submicron
particulate mutter. This generally occurs in modern plants
with strictly controlled emissions, since the control equipment
primarily removes the larger particle sites, while submicron
particles pass through.
Instrument Output
The instrument has a 0 to 20 milliampere output directly
proportional to optical density units, with an elevated in-
strument zero at 10% full-scale (2 milliamps).
Figure 6 shows the relationship between the optical density
output of the instrument and the more familiar scales of opac-
ity or transmittance. Optical density (D) is defined as the
logarithm (base 10) of one over transmittance (T):
D - log 1/T - -log T (i)
Since opacity (O) is defined by 0 - 1 - T, the relationship
with optical density can be expressed as:
D - -log T - -log (1 - 0), or
T - 1 - 0 - 10~» (2)
If Tor (1 - 0) is plotted ona logarithmic scale, a linear correla-
tion is obtained as shown in Figure 7. The above relationship
is known as Bouguer's Law, equivalent to the well known
Lambert-Beer's Law for the measurement of absorbance by
colored solutions. It can be shown that the optical density
for the case of light attenuation by a smoke or dust aerosol
like the absorbance for the case of light absorption in soh>
tions, is proiwrtional to the jwthlcngth (d) and the concentra-
tion (r) of the light attenuating material.
D- k
(3)
This relationship is used to correct the measured optical den-
sity values (DO for the measuring distance (rf,) at the instru-
ment installation site to the values (D,) applicable for the
stack-exit diameter (d,). Since a folded-beam instrument
measures through twice the smoke width at the installation
site, the distance dt must be taken twice as follows:
dt/2dt
(4)
\^/
The corrected optical density values can then be converted to
opacity units by means of the graphs in Figure 6 or 7, or equa-
tion (1), or by using readily available tables (Handbook of
Chemistry and Physics) or nomographs. An electronic
opacity converter and readout unit which is intended for in-
stallation on the instrument panel in the plant control room
m
(.t (J dJ 14 U 1J MUM M 10.1
•iillll DIMMH .MOMS
Wi.ilre I. Llftrt attenuation of a polydlspef se aerosol as a function of particle size.
34 Journal of trw Mr Pollution Central AsMctetfon
-------
IB available. It allows the selection of a meter readout in
terms of either optical density at the measuring cite or opacity
at the stack exit, and either or both of these outputs can be
recorded on a strip chart recorder. The available measure-
ment ranees indicated in Figure 6 are single pass rrjui valents of
the instrument's double pass measurements.
Correlation with Dust Loading
According to llongucr's L-uv, the optical density instrument
readout is directly proportional to the dust concentration in
the gas. The constant of proportionality differs with the
density of the particulate matter, its size distribution, aiul its
optical properties. The constant can be calculated if all data
nre known.'-'-* In practice, it is easier to c^jcrimentally
determine the proportionality constant for each installa-
tion.'•'<>-"
Empirical calibration of the transmissometer in tonns of
particulate concentration requires at least OIK- data jxjint ob-
tained by stack sampling, using an approved sampling train
and method (KPA method 5). The average of the trans-
missometer readings over the |>criod of the stack sampling
test equals the measured dust concentration in mg/m* or
gr ft' at actual conditions. A straight calibration line is
drawn from the origin through the ex|>erimental point.
Calibration in terms of dust loading is valid only as long as
the particle size distribution and other psirtii-iilntc pni|M>rties
% con-
fidence level are indicated in the figure. Figure Kb shows the
name calibration curve after correction to standard conditions
(teni|ierature, pressure) and dry gas. The corrected calibra-
tion curve can Ix1 useil when gas temperature, pressure, and
humidity are constant. Figure 9 shows a similar calibration
1J
O.f
«.l
e.$
0.4
0.9
O.I
0.1
. %
10
I I
TrmminMC*, % 100 W M TO M M 40 M M 10 0
"K»l» OMlwd Lhw* H*Brn*nl LItnlii »l Wnfte PCM
M««tuf*m«nl
Figure C. Relationship between optical density and
opacity or trHnsriiittance (linear «cal«).
September 1974 Volume 24, No. 9
s
M 1
1 1
0 1
1
• 1
X
0 1
i i
i
« 7
X
« 1
1 1
r i
V 1
« «
3 •
1
0 1
X
D I
4 1
1 '
0 <
X
« 1
* 1
%fim
1
0 3
/*
0 T
( «
•»*•»•»
1
« 1
/
'
0 1
r 1
i
« i
^
^
0 •
* 1
t
I
0
*
.•f
"I
..«
1 J
Figure 7. Relationship between optical density and opacity or trans-
mittance (logarithmic scale)
curve obtained on a lignite-fired boiler in Germany, and
Figure 10 shows a .similar calibration curve for a bituminous
coal-fired jxiwer station.
The system is being used in numerous installations in the
United States and in Kiiro|H> for the continuous monitoring
of both opacity and paniculate concentration, based on the
correlations established Ix-tween the optical rending and the
dust loading. In some states of the German Federal Re-
public the instrument is approved for compliant* monitoring
on specific large emission sources. In this application the in-
strument calibration in terms of particulate concentration is
cheeked by manual testing once it year. In evaluating the
monitoring record, credit for the possible measurement error
is given.
Table 1 summarizes the levels of error observed in a number
of correlation lines for typical emission sources. Four dif-
ferent definitions of error have been applied. Values have
been calculated from the available raw data using a computer
program.* The error definitions are as follows:
A. Standard deviation is the root of the mean.
B. Ty |»e 1 error is the 9.r>% confidence level that the true mean
of'all observed optical data for n given particulate concen-
tration will lie within the limits.
C. Tyjx- 2 error is the 05% confidence level that the next one
observation will fall within the limit.
D. Ty|K> 3 error is tlie 95% confidence level that 95% of all
possible observation* (05% tolerance) will full within the
limit.
In Europe type 3 error calculation is typically nppliett, while
in the 1T. S. the type 2 calculation is most common. The
smallest error level is obtained by the ty|x« 1 method, As a
jH-rcentagv of the measured mean particulate concentration,
the ty|M-1 error level ningesfrom 5 to 21.1%.
Itecuuse transinissometer data arc typically correlated with
1 hr stack sampling data, an individual duta |x>int in the con-
tinuous transmissometer recording can be defined as a 1 hr
35
•Th« author trmnki Gtrald McGowmn fur his uulitannln providing th«
cominitrr data. The ormr mlrttlaliun in avaiUlile at a Mrviee from Lear
8i*«l«r. Inc. Knvinmm«nlal Trrlm»li>Ky Divinion.
tet
-------
MO
1*0
• Tn
(Without Onm)
-•.11
•.it
*.•• o.i
Optical
».«
*.i
t.tl
Mt
w
I.
• — Norm* Operating Mod*
i — Nornul Mod* Wllh Deviation*
a— Mroct Mod* (Without Oryw)
•»— TramMomlModt
0.01 (1 Oil 0.1
Oallcal Density - flitfta *M«
O.M
Figure I. Relationship between optical density and
participate mass concentration for a cement plant.
a. Actual conditions.
b. Standard conditions.
average reading. The continuously recording instrument
easily allow* determining 8 hr or 24 hr average*. The effect
on the error probability is therefore equivalent to averaging
8 or 24 individual data points. In Europe the instrument is
now used in many applications in conjunction with an inte-
grator which provides simultaneous outputs of 1, 8 and 24 hr
continuously ujxlaU'd averages. If any of the averages ex-
ceeds a predetermined value, controls are activated auto-
matically. The longer term averages improve the accuracy
and reliability of the emission data recorded.
The correlation data available from different emission
sources allow a comparison of stack opacities resulting from
different emission sources at equal paniculate concentrations
and stack diameters. Some calculated opacities for a con-
centration of 150 ing/Nni1 (0.071 gr/scf) and a stack exit
diameter of 3 m (10.12 ft) are summarized in Table II.
Scop* of Applications
Use of the instrument for the continuous monitoring of
particulatc mass concentrations has been proven in the fol-
lowing categories of emission sources:
coal and oil-fired [rower stations
residual fuel oil-fired industrial boilers
Kraft recovery and hogged fuel fired boilers
refuse incinerators anil teei>ce burners
wet and dry process cement kilns
catalytic cracker regenerators
glass furnaces
turbine engine test cells
coke ovens
electric arc furnaces
When installed following electrostatic precipitators, the instru-
ment precisely records the fluctuations resulting from precipi-
tator rapping. It indicates malfunctions and allows proper se-
quencing of rapping and adjustment of the precipitator for
maximum ixrformance (fine tuning).1*
The instrument system also monitors sodium losses on
Kraft recovery boilers" and catalyst losses from catalytic
cracking regenerators. The instrument's capability is with-
out equal for accurately measuring low opacity values as
required for cement and glass plant emissions and turbine
engine tests. In monitoring the combustion process of oil
fired facilities or waste incinerators, the instrument can be
reliably used for the automatic control of overfire air, fuel
additive, or other adjustments.
Following a fabric filter system, the instrument clearly
shows a surge of emission whenever a compartment comes
back on line after denning. A bag leak is signalled by a rising
baseline of emissions but a sharp drop to normal levels when-
ever the compartment with the leaking bag is closed off for
cleaning.
TaMe I. Error levels for correlations between optical density measurements and particulate mass concentration.
Error Level (mg/Nm') At Mean of Part. Cone.
Cement
Bituminous coal
Lignite
Municipal Incinerator
Kraft recovery"
Hogged fuel"
Bituminous Coal"
No. of
observ.
39
20
36
IS
12
13
11
Correl.
coeff.
0.985
0.760
0.915
0.909
0.957
0.750
0.974
Mean part.
cone.
(mg/Nm')
179.9
322.3
111.2
90.3
76.4
206.0
252.3
Std.
dev.
±13.9
±85.5
±31.4
±29.5
±12.6
±61.8
±56.4
95% Confid.
True mean
±9.0
(5.0%)
±40.2
(12.4%)
±10.6
(9.5%)
±16.4
(18.2%)
J16.1
(21.1%)
±39.0
(18.9%)
±38.4
(15.2%)
95% Confid.
Next single value
±57.2
(31.8%)
±184.0
(57.1%)
±64.6
(58.1%)
±65.7
(72.7%)
±57.9
(76.0%)
±145.6
(70.7%)
±133.2
(52.7%)
95% Confld.
95% of all
poss. values
±68.6
(38.1%)
±475.4
(147.5%)
±78.1
(70.2%)
±88.5
(98.0%)
±81.6
(106.8%)
±201.2
(97.6%)
±379.5
(150.4%)
170
36
Journal of the Air Pollution Control Association
-------
LI|«M*
I
I
8
0.10
Table II. Companion of stack opacities for different emission
sources under equalized conditions.
0.10 (.is
Optlul DwMlty -
Figure I. Relationship between optical density and par-
tlculat* mac* concentration for a llgnit* fired boiler
(standard conditions).
•llu«4nou» Coal Find Boiler •nUtleno
400
200
«
•fl.os/y
71
i
M
'//
/
W
y
o.o* 0.1 e.tt 9.1
Oplteal D*n*lty - Slngl*
•.II
Figure 10. Relationship between optical density end
participate mass concentration for a bituminous coal
fired boHer (standard conditions).
The instrument's continuous output signals for both opac-
ity and optical density, corre.spondinp; to particuluto mass
concentration, can be used as inputs to a total emission moni-
toring system. Other sensor inputs required inohulc tem-
perature, humidity, pressure, and gas flow rate, as well its other
emission parameters such as sulfur dioxide and nitric oxide
content. A small data processor or controller can then cal-
culate mass emission data (Ib/hr or Ib/.MBtu) and applicable
averages (e.g., 10 min, 2 hr, and 8 hr averages) and provide
continuously updated printouts. Such complete monitoring
systems will be used in the future.
There are some limitations to the applicability of the on-
stack traiismissometcr. Water droplets in the gas are mea-
sured as if they were paniculate matter. Unless mist omis-
sions arc to be measured, efficient demisters must be employed
after wet scrubbers, or a portion of the gas must be reheated
prior to measurement in a by-pass duct.
Similarly, the instrument cannot correctly measure the
opacity of emissions which form visible plumes after the gas
exits from the stack (such as sulfuric acid mist or vapors
which condense on contact with the cooler air).
Soptwntoa* 1974 Voluitw 24, No. 9
Emission
source
Cement
Bituminous
coal
Lignite
Municipal
incinerator
Kraft
recovery
Hogged fuel
Bituminous
coal
Mean
part.
cone.
(mgyNm1)
179.9
322.3
111. 2
90.3
76.4
206.0
252.3
Single
passO.D.
at mean
of part.
cone.
0.1029
0.0944
0.0580
0.0235
0.0746
0.1290
0.1432
Diam. at
measur-
ing site
(m)
1.95
3.25
4.00
3.66
1.52
4.88
Calcul. for
150 mg/Nm1 and
3 meter stack diam.
O.D.
0.1320
0.0722
0.0293
0.1200
0.1854
0.0523
%
Opacity
26.2
15.3
6.6
24.2
34.8
11.3
References
1. K. Sick, (/. S. Palml \a. :{,fi17,7-VJ, issued November 2, 1071-
2. K. W. Btthne, "Investigations into the directional dependence
of photoelectric smoke density measuring instrument*."
Staub 31: 22 (11171), (in Kngli.sh).
3. "Stundfirds of j«?rfon, April 1072 (Knvironmental Research Corp., St
Paul. Minn.).
7. W. 1). Connor and J. II. Hodkinson, Optical Pro-prrtiet tmd
Visual Effects of Smiikr Plumes, Knviroiunental Protection
Agency, Ollice of Air Programs Publication No. AP30 (Co-
operative Study Kdison ICIcctric Institute and Public Health
Service, 1067).
8. M. J. Pilat and I). S. Kn.sor, "Plume opacity and particulate
mass concentration," At mm. Environ., 4: 103 (1970).
9. IX S. Knsor and M. J. Pilat, "Calculation of smoke plume
opacity from paniculate air pollutant properties," J Air Poll
Control Asuoc., 21: 4!Nj (1971).
10. T. F. Hurley and 1). L. II. Bailey, "The correlation of optical
density with the roncenl ration and composition of smoke
emitted from a Lancashire boiler," J. Intl. Fuel. 31: 534
(1058).
11. L. Diiwel, "Coinpurative Sttidios of Different .\fe*«uring
Principles for the Continuous Monitoring of ParticuUte
Krnissions from Lipvitc Fired Uoilers," Proceedings Second
Int. Clean Air Congreti, Kdited by II, M. Knglund and W. T.
Berry. Acaort, 1973.
1A. W. A. Schneider, "Opacity monitoring of stack emiwioos:
A design tool with promising results/' The 1974 etietric
utility ... Generation Plankook. McGraw-Hill, New York,
1974, pg. 73.
Dr. Bcutner is a Vice President of the Environmental
Technology Division of Ix;ar Siegler, Inc., One Inverness
Drive KasVKiiglewood, Colorado SOI 10. Since 1971, Dr.
Ueulner has been responsible for the marketing and appli-
cations development, efforts for the division's pollution-
nicinitciring instrumentation. His present responsibility is
business manager for Lear Siegler's air pollution control
equipment. This is a revised version of Paper No. 73-169
presented at the With Annual Meeting of APCA at Chicago
in June 1073. The author thanks Ernest E. Mau for his
assutance in the preparation of this poper.
37
-------
Instrumental Method Substitutes for Visual
Estimation of Equivalent Opacity
Herbert C. McKee
Southwest Research Institute
Many air pollution control regulations limit the emission of visible effluents, based
on the visual observation of "equivalent opacity." Because of difficulties en-
countered in wing visual observation, the Texas Air Control Board developed a
method of calibration which made it possible to use an instrumental method for
measuring visible emissions. A legal regulation based on this instrumental method
has been in effect for almost two years. Despite 'minor difficulties in calibra-
tion and maintenance, results have been satisfactory. The use of the instrumental
method avoids many of the difficulties inherent in using a regulation based on visual
observation, and continued use of the instrumental method is anticipated.
The regulation of emissions of dust
and other particular matter is a major
portion of most air pollution control
programs. This is usually done by
either or both of two different methods:
(1) regulations based on the weight of
material emitted, and (2) regulations
based on the optical pro|>crlies (opacity)
of the emission.
The visual appearance of smoke emis-
sions ha> bveu regulated for over 70
years by the use of the Kingclmann
chart to evaluate the density of gray and
Muck smoke.1-* More recently, the
Mime principle has been extended in the
control of emi-sions other than gray or
lilark I'V Utilizing the concept of "equiv-
nlent opacity."1 It has been (Miniated
that between To and 101) governmental
control agencies now use this concept to
control visible emissions. These regu-
lations usually specify that the emission
should not obscure the view of an obser-
ver to a greater degree than the obseura-
tion which would be caused by gray or
black smoke of a specified density a«
measured by a Ringelmann smoke chart.
To aid in evaluating equivalent
0|>acity, good correlation has been shown
between visual estimates by a human
observer and instrumental readings
obtained with a transmissomcter
installed in the staek of a social smoke
generator.4 This principle has been
used to train air pollution inspectors in
the estimation of equivalent opacity.1
It has been shown that the errors inher-
ent in a subjective observation can be
(•really minimized in this way so that
visual estimates are sullieiently repro-
ducible to form a basi> fur lenal control.
This principle has also been upheld in
the courts.
. Despite the use of smoke generators
as training devices, however, there is
still some uncertainty in making visual
observations of equivalent opacity.
Furthermore, such observation* can be
made only with extreme difficulty at
night or during cloudy or rainy weather.
Therefore, the Texas Air Control Board
undertook to develop an alternate
method of measurement which could
overcome at least some of these limita-
tions and could provide more accurate
and reproducible results. This method
has now been in use for some time and
is specified by a legal regulation of the
Board as a substitute for visual e-ti-
mation.'
Principle of Method
Since the reason for controlling emis-
sions on the basis of equivalent o|>ncity
is to limit the emission of material*
which cause absorption or scattering of
light, the direct measurement of licht-
scattering pro|H>rties was selected »»tlie
basis for developing an instrumental
method of measurement. Instruments
have l>een in u.-c for many years which
measure light transmission aciu.-« a
stack a.s an aid in estimating the amount
of material emitted or the density of
black smoke. Most of these in.-tru-
ment.s include a liizlit source and also a
photocell, lioloinetcr, or other optical
measuring device: these are located on
opposite sides of the stack in such a way
that the lidit U'uin pas«e.* through (he
stack gases which are lienus emitted.
The amount of light which pa«fs
through the plume is measured, and the
result is cxprc««cd as percent transmit-
lance compared to a measurement with-
out stack gases present.
Instruments of this nature are avail-
able from several suppliers, and there-
fore it wn« decided to utilize this ty|x- of
4M
Journal ol the Air Pollution Control Association
-------
instrument as a Mubstitute f«w tlir vi-
sual estimation of equivalent opacity.
By installing the instrument in a duct or
stock, where the optical proiwrties of tlie
fas stream can be measured prior to
leaving the stack, a continuous record of
optical transmittance can IK* obtained.
Since the optical propertie* depend
primarily on the smaller particles pres-
ent in the gad stream, considerations of
isokinctic sampling do not ap|ky buck-
ground, emission condition*, or other
factors which influence visuul observa-
tions.
Calibration
In order to avoid error- due to < liaitur<
in exit velocity or other emission condi-
tions, the |x»rmisstblc optical projicrties
of the emission were established on the
basis of the total volume crnittvd. In
this way, I hi- total contribution of the
emission to ihe optical propertii"* of the
community atmosphere was tin primary
controlling factor.
20
ho
i
2 5 25
10.000 100.000 l.OOO.OCO
Volumt tmiiwd, elm
Flfur* 1. light path required for 70% trint*
mitunce.
Augutt mi Volume 21. No. 6
The inst-riiment re*>|>oit*e aUo varies
de|>eiidingoit the light path across wliich
the measiiremr-nt i.< mnilc. I» eonven-
ttoual in-tatlations, the light path usu-
ally is not extended the full width of the
stack or duct in which the instrument is
installed since disturbances in the flow
pattern next to the wall might cause
erroneous readings. To calculate a
calibration curve, an exit velocity of 40
fps wns arbitrarily assumed so that a
direct calculation could be made of the
assumed diameter of the plume, and
thus e>tubli>h the length of the light
path across which the required trans-
mittance would be measured. The
required minimum transmittunce was
selected ns 70^, this twing somewhat
more restrictive than the iinual opacity
limit equivalent to a \o. 2 Kingclniumi
reading. Figure I illustrates the re-
sults of this calculation, and >hows the
li^cht path fora minimum tr:m.»mittaiu'C
of TOTi at any flow rate between 10.000
and l.OOIl.LHJO cfm. This volume U
biiM-d on tin- total volume of gunc* emit-
ted includins; air, combustion ga>es,
ga.seous impurities, and all gaseous mat-
ter combined, but excluding water or
water va|»or, calculated at the pitssure
and temiK'ialure existing at tin' point of
measurement. This graph, thru. s|>eci-
fiex the light path across whii h the mini-
mum acceptable trati-mittuncc to deter-
niiiie legal compliance a ~ta< k installatioos
will not permit the UM- of this lenctli of
tight |>ath. a method wus mi'ilul to con-
vprttlicTlX'i traiismittaucc loan eipuvn-
teiit hgure over some other li»bl path.
This wa- ilniic by the u-«c of the follow-
ing equation:
-log T - U
where
T - trunsmittance
I - length of light path
k — con>tant
In this equation, k can be evulunU-inittunce for some other
length of light path.
Figure 2 is bu.Mt pnth
olln-r than the length "(x-cified by Figure
I. E\|N-nence lia.s shown thai tlui
cc|iiutiossible that extrapola-
tion beyond these limits may introduce
some degree of error.
Precautions
Certain precaution.-! should be kept in
mind in the use of thin instrumental
method. For example, gases high in
moisture content should be measured at
a |>oint where the gas temperature is
ulkive the dovv point to prevent eotideu-
sation; otherwise, loss of light truiismit-
tance mny occur due to the presence of
condensed water droplets in the gas
stream. Certain situations may also
ari.se in which the method cannot be
used satisfactorily, such as the following;
t. Emissions may change in char-
acter after emission to hvconu.1 more vis-
ible (so-called "detached plume"), so
that an omission which is invisible in the
stack may in fact cause deterioration of
visibility in the ambient atmosphere
following emission.
2. Different omissions may mix and
react in the atmosphere to form aerosols
which restrict visibility, although each
emission may be essentially invisible
when first emitted. A familiar example
is the formation of a highly, visible aero-
sol of ammonium chloride by the reac-
tion of ammonia with either eliloriue or
hydrogen chloride.
U'hore ilu-so or other coiulivum* make
it impossible to UM; this method. visual
iiis|M-ctiim or some other alternate must
lie found. However, so far these excep-
tions have occurred only infrwHirntly.
Illustrative Example
Tluoimh the cooperation of the Dow
Uii-micnl Cuini'iiny, dutu lire prex-nu-d
lirtr in .|in\v a typical illu*tration of (hr
Ot
40
-------
u*e of this method of measurement. An
instrument supplied by the Bailey Meter
Company was installed in the stack
carrying flue gases from a series of lime
kilns at the Freeport, Texas plant of
Dow Chemical Company. Figure 3
shows a typical chart recording during a
24-hr JHTKM!, illustrating the minor var-
iations in transmittancc during this time
when the average transmittance across
the 5-ft light path of the instrument was
around 90%. Note that the recorder
wad set to record in the range of 70 to
100% traiismittanec, with 70% at the
periphery of the chart and 100% at the
center.
Total volume of xases emitted is
approximately 130,000 cfm, although
this naturally varies to some degree with
changes in operating conditions. At
this flow rate. Figure 1 indicates that a
path length of 8.2 ft would he correct for
measuring the required 70% transmit-
tance. Since the instrument was
installed with a 5-ft light path, Figure 2
was used to determine the equivalent
reading with this installation; this indi-
cated that the transmittance should not
be less than approximately 80%, which
corresponds to a 70% transmittance
over a light path of 8.2 ft. Thus, the
90% transmittance shown in Figure 3
illustrates better precipitator perform-
ance than the minimum required to
meet the regulation. This instrument
has been o|>erated for several months
and has provided a convenient means of
monitoring the o|>eration of the precipi-
tator to detect any minor changes indica-
ting a need for maintenance or adjust-
ment. The only instrument mainte-
nance has been an occasional cleaning of
the windows on the liuht source and bo-
lometer, and instrument stability and
reliability have been re|x>rted a*
satisfactory.
Advantages of Instrumental Method
In the past two years, 40 to 50
instruments have been installed in vari-
ous industrial plants in Texas, for use in
meeting this now regulation. Processes
include lime kiln*, cement plants, fertil-
izer driers, regenerators in catalytic
cracking units, and others. liased on
the experience which has been accumu-
lated, the instrumental method appears
to ixissess the following advantages:
1. The instrumental mctln.nl is com-
pletely objective and therefore is not
subject to the errors inherent in subjec-
tive evaluations by human obr-crvers or
to variations among duTctvnt individ-
uals making vi-ual estimates.
-. The instrumental method appear*
to IK- more accurate than visual nbiserva-
lions. With adequate maintenance anil
calibration of the instrument, it ap|x*ars
to be po-sible to maintain ,tn accuracy
of a few percent. This is ln-tter than
the accuracy generally obtained with
visual estimation, e*|>ecially with high
1*0
I. Twenty-four hour chart record,
showing typical MntmitUnc* m»i»uf«m«nt.
transmittance values above 60 percent
which are required by many regulations
now being written. Previous experi-
ence has indicated that an equivalent
opacity of Ringclmann No. 1 is more
difficult to estimate than No. 2, which
means that transmittance values in
excess of 60 to 70% may be subject to
considerable inaccuracy if measured by
visual estimation.4
3. An automatic instrument can be
used at all times, and the results are not
affected by sunlight, cloud cover, dark-
ness, or other conditions affecting visual
observations. Readings can be ob-
tained on a 24-hr basis.
4. Continuous measurements can be
recorded automatically at less cost than
the cost of frequent observations by
trained human observers.
5. Since results arc available on a
continuous basis, they can be used as a
means of process control for continuous
processes. Thus, the plant operator
can be aware of any malfunction of pol-
lution control equipment immediately
in order to take necessary corrective
action. This is not possible with regu-
lations based on the weight of dust
emitted since stack sampling to measure
weight if tedious and time-consuming
and subject to a time lag in obtaining
measurements which may be as much as
several days.
Thce.\|>erieiire todateliasnot revealed
any scriou- problems in the operation or
maintenance of the instruments. The
major problem i» tiiat of rechecking cal-
ibration on production units which are
Ojieratcd continuously for many months,
and various ways to accomplish this are
uniler study, (ilass surfaces exposed to
flue gnse> niu«t IT clcam-d oecasitiMully
although tin- can U1 mlm-ed by the use
of an air bleed which mmiimio the con-
tact of dii»t laden ga«cs with I he window
surface!*. Plant operators have re-
ported no uiiii-ual maintenance problems
winch cannot U- bundled adequately
by the average plant instrument depart-
ment.
Because of the advantages of this
method, the Texa.s Air Control Board is
considering making this method manda-
tory for all industrial sources subject to
regulation on the basis of opacity,
except for very small o|>erations where
the cost of installation ami maintenance
of an iiistnimpjit would be out of propor-
tion to the tola-fit received. A figure
of 10,000 cfm has been mentioned as a
minimum size for mandatory installa-
tion, but this factor is still under consid-
eration.
Acknowledgment
The author wishes to express appre-
ciation for the assistance of the Texas
Air Control board staff in the develop-
ment of calibration procedures and
other details in connection with the new
method which is outlined. In addition,
appreciation is also expres-ed to the
Texas Division of Dow Chemical Com-
pany, for (icrmissiou to describe the lime
kiln installation which illustrates the u.*
of this method, ami for the illustration
furnished.
Reference*
1. Kmuelmann, M., "Method of esti-
mating smoke produced by industrial
installation*," Rtv. Tirkniiiuf, 2fr»
(June ls».«0.
2. U. S. Department of the Interior,
Bureau of Minrn Information Circular
7718 (AiiBiist l!».V.J.
3. State of California. Health and Safety
Code, Chanter 2, D»vi>i«n 20, Section
24-.M-.' fl'.il7>.
4. Conner, W. 11 and 1 lodkin-on, J. H.
Optical Propirtim anil \'i3tial Efftrt*
of Smoki-Stark Pttimr*, PnMiration No.
»99-AI'-:JO, f. ?s. I>«bli<: Health Ser-
vice Uilfi").
5. Coons, J. I)., Jame-, II. A., Johnwn,
H. C., and \Vnlker, M S., "Develop-
ment, Calibration, and I'-r of :i Plume
Evaluation Training t'nit." J- Air
Poll. Canlntl .4.««»-., 15, I!W (May
1%:»1.
0. HfCiilatii>n I. "Control of Air Pol-
lution from Srnukr. \'isihlc Knn—ion-
and lsii>pfii.
Dr. Mi-Kee, »bi« i> A^Mnni Di-
rvi-tur. Departmeut of t'hein^try
11 nd Clu-niiiul KiitsiiiiTring nf the
Soulhwesl l!(-earrli In-nniir —
I IIHI-IMII. ;iNn .<>rr<— ;i- < 'K unii.in .if
ilieTi'XU' Air Coiiirol |ln:iri|. Tlii«
|I:>|»T w:i- pre-entiil at ll«- 1'i.lnt An-
iiuat MII-IIIIV ..f Tl»- Air Polliiti.ni
Coiiirol A->i'c. ii- Paper NIL 7n->-4.
41
Journal of th« Air Pollution Control Association
-------
Reprinted from POLLUTION ENGINEERING, November 1978
Opacity monitoring technique
predicts baghouse maintenance
JULIAN SALTZ and LEE COTLER
When a baghouse is operating properly, typical
collection efficiencies better than 99 percent can be
expected. However, if a bag becomes worn or if a break
occurs, the emissions will increase, often above the legal
allowable level. A major bag rupture can also allow a
substantial quantity of valuable product to be emitted
and lost to the atmosphere. Therefore, it is important
for several reasons to know the instant a break occurs.
A time delay device can be installed in an opacity
monitor and can be set so that a rupture can be
detected from 0.5 sec to 2 min after occurrence. A relay
in the opacity measuring control unit can then be used
to disconnect power to the ID fan of the baghouse,
• thereby preventing product loss and opacity violation.
Opacity and mas* flow
An opacity measurement is taken by projecting a
well-collimated light beam across the diameter of a
t'igure I. Common duct of a 5-compartmtni baghouse. Opacity
instrument is located under the triangular weather cover.
Julian Salt: is president of Datatest. Inc., designer} and manu-
facturers (ij instruments for measuring air pollution. He has a
H.S.t.h'. degree and lias an e\tensive background in instrumen-
tal ion design.
l.ce (.'oiler is a technical specialist with Datatest, Inc. He has
many years of experience in manufacturing and engineering in
the electronic.1; instrumentation field.
process outlet pipe or exhaust stack. Particles in the
effluent will block or absorb part of the light, thereby
reducing the amount of light that reaches a receiver
unit.
In addition, it is possible to relate the mass flow
(g/scf) to opacity for a specific process.1 In a study
made on a municipal incinerator in Minneapolis,2 the
relationship of mass flow to opacity was found to be:
Opacity
where:
ity= 1-L
light with blockage
light with no blockage
100
w =
40
43
NV= paniculate mass concentration
of the plume, g/m3
Ki= plume parameter. cmj/mi
P = average paniculate density, g/cm!
L= plume diameter, m
OP= plume opacity
The value Ki for the incinerator operation varied
from 0.33 to 0.5. For this operation, the opacity for a
mass flow of 0.05 grains/scf varied from 8 to 12
percent.
Baghouse monitor
The instrument shown in Figure 1 is used to monitor
PVC emissions from a baghouse with a capacity of
50,000 cfm. The control unit is approximately 200 ft
from the receiver at ground level. All adjustments, such
as zero, span and set point alarm, are made at the
control unit.
Using this technique, schematically shown in Figure
2. the opacity of the effluent is measured to determine if
it is within acceptable limits. If a bag develops a hole,
the opacity insirument will detect it. The output of the
opacity meter is connected to a recorder and a day-by-
day record is made of the effluent opacity. Each time
the bag is cleaned, a small increase in the emission level
occurs. The peaks of these emissions may be observed
on the recorder. By monitoring the signature spikes of
an individual compar'ment and observing the
progressive increase each time the compartment is
cleaned, it is possible to see a hole enlarging or the
effects of increasing porosity of the bags. Using this
technique, it is possible to predict weeks ahead of time
when baghouse maintenance is required.
Operation and control
As shown in Figure 2, the electrical signal from the
photocell in the receiver is divided by the signal from
NOVEMBER 1978
-------
the light source in the transmitter. The resultant is
subtracted from 1 and this is the opacity signal which
goes to the meter and recorder. An alarm level may be
set for any value of opacity from 0 to 100 percent.
Low level measurements
The baghouse has a unique characteristic that allows
for low-level measurements of opacity. If there is a
small hole or opening in a bag, or if the bags have
become thin or porous, the baghouse cleaning process
will release some of this material into the outlet pipe.
This emission may be very small, in the order of 0.1
percent opacity, or above 0.0005 g/ft3. It is impossible
to obtain such a low level measurement using standard
opacity measuring methods. However, a high mass
electrical filter was connected to the output of the
opacity system shown in Figure 2, along with suitable
impedance matching circuits. Using this technique, drift
due to soiling of the optical lenses exposed to the
effluent was eliminated and low-level measurements
were made as shown in Figure 3.
In this particular case, five baghouse units were
connected to a single pipe which the opacity meter
spanned. The 4-in. chart is calibrated for 10 percent
opacity full scale or 0.1 percent per small division. Note
the variations from compartment to compartment,
from a low of 0.3 to 1.4 percent.
As the spikes on the strip chart recorder increase in
amplitude, a bag problem is being reflected. In this
sequentially pulsed, multicompartment installation, the
amplitude increase pinpoints the compartment with
problems.
Therefore, operators can now use this opacity
measurement technique 'to predict future problems such
as bag blowouts or excessive emissions. Equally impor-
tant, this technique can be used to measure extremely
low levels of materials which are hazardous or toxic.
Bibliography:
I. Ensor and Pilot. "Calculations of Smoke Plume Opacity from
Paniculate Air Pollutant Properties." Journal of Air Pollution
Control Association, No. 3, 1971.
2. Metropolitan Waste Control Commission, Minneapolis,
MN. Report No. 7065.
Figure 3. Low level measurement of effluent from a 5-compartment
50,000-cfm baghouse. Note increasing measurements in comparments I,
2 and 4. Steadily rising levels would indicate a bag beginning to break or
porosity increasing.
10 i
Baghouse Compartment Numbers
Compartment Numbers Cleaning Cycle - 1 in./ hr Chart Speed
Figure 2. Electro-optical diagram of an opacity instrument.
POLLUTION ENGINEERING
44
41
-------
AIR/WATER QUALITY |
Continuous onstack monitoring
of participate proves feasible
New optical instrument opens way to
continuously and accurately monitor
particulate and visual emissions from
kraft recovery and hog-fuel boilers
•y J. C.CRISTELLO and J. E. WALTHER
D Continuous monitoring of particulate emissions from
boilers is becoming important for a number of reasons.
First, a continuous and accurate record may be a necessity
in proving that boilers are in compliance with visual and
mass emission standards. Secondly, new emission control
equipment can readily be evaluated to determine if it meets
the manufacturer's specifications. Lastly, continuous moni-
tors can aid boiler operators in optimizing the performance
of the boiler to reduce emissions.
At one time, stack emissions were primarily graded by
visual measurements of smoke emissions by the Ringelmann
method. The Ringelmann text subjectively measures smoke
density by visually comparing the darkness of a plume
against shades of gray, representing different-levels of
opacity. Most air pollution standards now specify the limits
of stack emissions in both visual and mass-volume concen-
tration terms. Thus, there is a need to measure particulate
emissions with an instrument capable of accurately correla-
ting particle concentration and visual observation with
smoke density.
During 1974 a study was undertaken to evaluate an
onsluck instrument capable of continuously monitoring
stack emissions from kraft recovery and wood waste
boilers. The test instrument evaluated was the Lear Siegler
Inc. (LSI) Model RM-4 transmissometer.1 Some of its most
significant features are: (1) automatic builtin calibration,
(2) double-puss measurement of the gas over the entire
stack, (3) and virtually maintenance-free operation.
Since the LSI measures across the entire stack diameter,
it is necessary to focus and zero the unit for each different
path length. Mounting and adjusting of the instrument
Mr. Cmtello was senior process engineer with Crown
Zellerhach Knvironmental Services, Camas. Wash., and is
now with Stevens, Thompson A. Runyan Kngineers Inc.,
Portland, Ore. Dr. Walther is supervisor of air programs.
Crown Zellcrbach Knvironmental Services, Camas. The
following is bused on a paper presented at the 1974
PNWIS-AK'A show, Boise, Idaho.
45
require about four hours. All of the initial work reported
was done with the transmissometer located at the site
normally occupied by the mill's bolometers or opacity
meters which utilize a slotted tube. This means that the
actual double-pass measurement distance was limited to 10
ft even though the flange-to-flange distance was greater. All
data reported in this paper are based on a total measure-
ment distance of 10ft.
Particulate sampling was done using either an instack
Hlter, a commercial EPA train or wet impingers. The
instack filter utilized a 70 mm, 0.3 micron, Type A,
glass-fiber filter. The National Council for Air & Stream
Improvement (NCASI) has demonstrated that results ob-
tained with the instack filter and the EPA train2 and those
with the wet impinger, 600°C residue, and the EPA train3
are equivalent. Sampling procedures used with the instack
filter and the wet impingers were similar to those described
in ASME Test Method PTC 27, while those used with the
EPA trains were similar to EPA Method 5. The major
variation from these methods involved sampling at the
point of average velocity rather than at several points. The
LSI RM-4 instrument reports measurements in optical
density units.
Boiler tests
The first test site was choien at mill A with an 800-tpd
B&W kraft recovery boiler. A three-field precipitator rated
at 98% efficiency preceded the transmissometer location.
Particulate samples were obtained at the main stack, just
prior to the bolometer ports using the instack filter with
wet impingers. A plot of optical density versus particulate
concentration is shown in Figure 1 along with the 95%
confidence limits.
The second evaluation was at mill B for a B&W hog-fuel
boiler rated at 300,000 Ib steam/hr at 600 psi. Particulate
control is provided by a cyclonic dust collecting unit. The
duct out of this unit is approximately 20 ft wide at the
point where the transmissometer was installed and the
particulate samples were taken. Three sampling ports were
available, each of which had a port at a quarter point. The
ports are perpendicular to the bolometer tube and the
middle port corresponds to the slot in the tube. Separate
particulate tests were made at each port.
A statistical analysis of the particulate measurements is
presented in Table 1. This analysis indicates that the
particulate concentration is not uniform across the duct.
Therefore, to continuously, accurately monitor the emis-
PULP 4 PAPER MAY 1975
-------
0.1
0.7
_0.6
o
g
0.5
0.3
a?
0.1
00 -O.WX -CM
!»*•«. r*
. *
//
•W
//
t
t
t
v/
•' / •'
///
'/s
y*
i
t
*
t
-
y,
*
t
f
legend
' ^
S
O InstKk filter
& Wei Impinqer.
600 C Rtiiduc
-~95*
Confidence limits
1
01 0? 0.3 0.4 OS 06 07
Front half particulate (X), grains/ltd cu ft
Figure 1. Mill A recovery furnace. LSI optical density
vs front half paniculate.
Middle Port
00 • 0.64 X -f 0.004
Rz • W. 5%
o West Port
O Middle Port
A East Port
o 0.10 a 20 a 30
Front half paniculate (X), grains/ltd cu ft
Figure 2. Mill B hog-fuel boiler. LSI optical density vs
front half particulate.
0,25.
0.15
0.10
0.05
1 1 / 7
00-1.ZKX0*.039 ,' / -
/ '
* / '
// /
,r
/
Double Ptjs
Path Length
UGtNO
95% tonlidence
Interval
0 a 05 010 0.15 0.20
F'om hall (MMiculatl ui l"(i I v-dito (In1 v,ct hulh lompera-
tine w.i\ .I)VMII I >'• I I nli.niirJ wjl.'i JiJ not appear to
be a problem because the measured water content was
approximately that predicted by wet bulb-dry bulb tem-
perature measurements. The particulate sampling train used
for this study was a commercial EPA-type unit. A plot of
LSI optical density versus paniculate concentration for mill
C is shown in Figure 3.
A highly significant correlation between LSI optical
density and particuhitc exists. Therefore, the LSI is suitable
46
-------
for use PS a continuous mass cnm\inn monitor. This implies
that the need lor traditional particulate tests would be
reduced to an occasional but periodic check to verify the
instrument calibration curve.
As shown in the appendix, the optical density and
opacity are merely mathematical transformations of the
same parameters. Therefore, a good correlation betwe n
optical density and participate assures an equal correlation
between opacity and participate concentration (Table 2).
However, a significant correlation between the LSI trans-
missomcter opacity and purliculatc concentration docs not
yield any information concerning the accuracy of the
opacity value. Accuracy of the instrument opacity would
be determined by correlation with the opacity determined
by a trained smoke observer.
Based on the data presented and casual observations of
the plumes for mills A and C, we were quite concerned
about the accuracy of opacity measured by the instrument.
After having the instrument checked out by a factory
service representative, it was decided to remount the
transmissometer at mill C in a location higher up on the
stack. This alleviated any unrecognized problems associated
with using the bolometer.
Appendix: Optical characteristics defined
The transmittance, T, is defined as the ratio of the light
flux out of the plume. I. to the light flux into the plume,
.
r
The transmittance is a function of the particulate
concentration, C, and attenuation coefficient, K, and of the
measurement path length. L. For poly-disperse particle size
distributions, K tends to be insensitive to small changes in
the size distribution.
T..-KLC (2)
The opacity, 0, plus the transmittance is equal to unity.
9 + T - 1 (3)
The optical .density, OD, which is a measure of the
decrease in visibility over some distance is inversely related
to the transmittance.
00 -..g^ (4)
By combining Equations 2 , id 4, it can be seen that the
optical density is also a 'function of the particulate
concentration and the measurement path length.
OD-KLCIqge (5)
It has been our experience that this definition of optical
density is not a density in the usual sense. Since optical
density is dependent on the total measurement path length,
this definition tends to create confusion. It may be more
appropriate and less confusing to redefine optical density in
terms of a true density that is independent of the
measurement path length and has the units of length per
unit length.
OD0 - K C log e (6)
If the optical density at the stack exit, 00, , is desired,
the measured optical density is adjusted to account for the
difference in measurement path lengths between the point
of measurement, L, and the stack exit, L,.
OD
.
L
(ODI
(7)
Equations 3. 4, and 7 may be used to find the in -stack
opacity at the stack exit.
9. - 1- (loo0 (t) (ODr1 (8)
!••
It is important to remember that the opacity as
measured within the stack may be significantly different
than that observed out of the stack.
Observation numburi
Number of observations
Mean visual opacity
Mean LSI opacity
Mean difference
Standard error of mean difference
t-test
1-62
60
41.4
47.9
6.5
0.73
8.89
65-141
74
34.7
24.1
11.6
0.56
19.14
Table 3: Hog fuel boiler: comparison of opacity measure-
ments made visually and with LSI transmissometer.
Determining accuracy of instrument measurements
Thereafter data were collected to determine if the
instrumental opacity measurements were accurate by com-
paring instrument and visual opacity readings as made by a
trained smoke observer (Table 3). The EPA states that
acceptable errors for certification of smoke observers is a
maximum of 15% and an average of 7.5%.4
Opacity measurements made visually are dependent on
the plume dimensions and color, the relative position of the
sun and the observer, and the background that the
observations are being made against. At the time the
measurements were first taken, the sky was clear, the sun
was to the observer's back and up in the sky; while at the
end of the observation period the sun was on the horizon
and at a horizontal angle of about 120° to the observer. It
is known that visual opacity measurements increase as the
angle between the sun and the observer increases. This
phenomenon was apparent in our observation. Considering
the inaccuracies of making visual readings for opacity and
using the data presented for mill C, it can be concluded that
the transmissometer accurately measures opacity.
The EPA has recently published proposed requirements
for continuous monitoring of stack gas opacity to be
recorded "and submitted in terms of the magnitude and the
number of one-minute integrated averages which exceed the
applicable standard."4 Needless to say, this kind of data
reduction would require a computer for data processing.
Furthermore, continuous monitoring of opacity/paniculate
will in effect serve to make current regulations more
restrictive due to a shorter time interval for measurement.
Consideration must be given to modifying standards based
on traditional particulate tests of one to two hours
duration.
The accurate and rapid response of the LSI unit also
makes it well-suited for special studies. As an example, we
installed the RM-4 on a recovery boiler, after a precipitator
but before a wet scrubber. This particular precipitator had a
history of subpar operation due to what we believe was
nonoptimal adjustment of precipitator operating para-
meters. The RM-4 made it possible to optimize these
parameters in a short period of time, without performing
standard particulate tests. Q
References
1. II. P. Beutner, "Measurement of opacity and paniculate emis-
sions with an onstack transmissometer. Air Pollution Control Assn.
Journal 24:865 (1974).
2. National Council for Air & Stream Improvement. "Comparison
of source particulate emission measurement methods at krjfl
recovery furnace stacks." NCASI Atmospheric Quality Impnivt
ment Bulletin No. 67. October 1973.
3 National Council for Ait & Stream Improvement. "Companion
of source particulate emission measurement methods at lime kilns
and smelt dissolving tank vents." NCASI Atmospheric Quality
Improvement Bulletin No. 64, May 1973.
4. "Stationary sources: proposed emission monitonnn and perform-
ance testing requirements," hejeral Register 39:32H$2. September
47
PULP ft PAPER MAY 1978
-------
IMPACT OF SULFURIC ACID EMISSIONS ON PLUME OPACITY
by
John S. Nader and William D. Conner
U.S. Environmental Protection Agency
Environmental Sciences Research Laboratory
Research Triangle Park, N.C. 27711
(919) 541-3085
Presented at
SYMPOSIUM ON TRANSFER AND UTILIZATION
OF PARTICULATE CONTROL TECHNOLOGY
Denver, Colorado
July 23-28, 1978
-------
IMPACT OF SULFDRIC ACID EMISSIONS OH PLUME OPACITY
John S. Nader «nd William D. Conner
Environmental Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina
INTRODUCTION
Emission standards for opacity and for mass concentration of par-
ticulate matter have been established for new sources and are applicable
to fossil-fired combustion sources1. Continuous monitors for opacity
(transmissometers) are required to be installed on these sources to
verify the maintenance and satisfactory operation of control systems
used to meet the emission standards2. Reference method 9 is the observer
method of measuring the opacity of the plume which forms as the parti-
culate matter exits the stack1. The Lidar J^ight detection and ranging)
technique is an electro-optical instrumental technique to remotely measure
the opacity of the plume3 "*. The transmissometers are installed in the
stack or in ducts leading to the stack. These monitors measure the
opacity of the gas stream in the stack or duct prior to its exiting the
stack.
The Stationary Source Emissions Research Branch (SSERB) of the
Environmental Sciences Research Laboratory has had in its program during
the past three years tasks to generate a data base of concurrent measure-
ments of in-stack gas opacity (Os) and plume opacity (Op) for emissions
from various industries. The purpose of these measurements was to
identify those industries wherein the plume and in-stack opacities do
not agree. Measurements conducted to date on combustion sources burning
coal with sulfur 12% show that Os and Op are comparable5 6. These
results would imply that no significant (observable effect on opacity)
physical or chemical transformation was occurring in the contents of the
gas stream as it was transported through the stack.
51
-------
Similar opacity measurements were made on a power plant burning oil
with 2.4% S (sulfur) and 200-600 ppm V (vanadium). In contrast with
opacity measurements made at sources burning coal or oil of lower sulfur
content the plume opacity was found to be significantly higher than the
in-stack opacity. At this oil-fired power plant a concurrent study was
being conducted on sulfuric acid emissions. The results of this acid
study support the conclusion that a physical transformation occurs as
the gas stream exits the stack and enters the atmosphere. The following
phenomenon is indicated: The sulfuric acid is above its dew point at
stack temperatures in excess of 150°C and does not affect the in-stack
opacity. When the gaseous sulfuric acid leaves the stack and is cooled
to ambient air temperatures which are below its dew point, it condenses
and the sulfuric acid droplets increase the plume opacity. Additional
studies have been conducted and are on-going to obtain more data and
understanding of the effect of sulfuric acid emissions on plume opacity
for various operating conditions, fuel composition, and control systems
for a number of fossil-fuel-fired utilities. This paper presents and
discusses the results of the above work that SSERB has conducted thus
far.
The sulfur oxides potentially present in the stack gas stream at
temperatures above the sulfuric acid dewpoint are as shown in Figure 1.
The free HjSOi, and SC>2 are not sensed in the measurements of the opacity
of the stack gas stream. In the plume with the temperature of the gas
stream dropping below the acid dewpoint and approaching ambient air
temperature, the free ^SOit condenses to form acid droplets. The con-
densed acid droplets and the acid adsorbed on the fly ash add to the
opacity of the plume. In our studies 03 was measured by transmisso-
meters and Op was measured by human observers or by a Lidar system; in
some instances, Op measurements were made by both of these methods.
52
-------
COMBUSTION SOURCE FEATURES
Plume opacity measurements were conducted In conjunction with emis-
sions characterization studies at 2 oil-fired and 3 coal-fired power
plants. Table 1 summarizes the physical and operating features of the
plants.
There is a marked difference in composition of the fuel utilized
in the oil-fired sources in contrast to the coal-fired sources. The
ash content of oil was two orders of magnitude less than the ash content
of coal. The sulfur content of the coal was from 2 to 4 times the
sulfur content of the oil. In addition, very high vanadium concentra-
tion (590 ppm) was found in the Venezuelan oil. Excess boiler oxygen
was typically in the 3 to 5% range except for Plant A which operated
at very low oxygen levels at about 0.2%. Oil-fired sources had no emis-
sion controls; however, fuel additives were used to minimize corrosion
problems and did provide some reduction in sulfate emissions7. Coal-
fired sources had either particulate emission controls (electrostatic
precipitators, ESP) or both particulate and gaseous emissions controls
(two-stage vet scrubbers).
53
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SAMPLING LOCATIONS
Sampling locations for all in-stack measurements were at a common
location between the emission controls and the stack except for Plants M
and LC. At Plant M all in-stack measurements were at a common location
in the stack proper. At Plant LC in-stack opacities were monitored in
breechings leading into the stack and all other in-stack measurements
were at the output of one of eight scrubber modules that operated in
parallel for the total boiler output of 820 MW. Each module in effect
handled about 100 MW of power output. Except as noted, plume opacities
were measured within one stack diameter of the stack exit.
54
-------
RESULTS
Emission data were obtained on particulate concentration, S02,
and sulfates under various operating conditions of the boiler (excess
02) and of the control systems (cutting back on electric fields of ESP).
Opacity data, however, were obtained concurrently for a limited number
of operating conditions. The Lidar systea was inoperative and under-
going repairs during the studies on the coal-fired sources. Plume
opacity data in these instances were limited to Method 9. Poor weather
conditions (fog) also restricted plume observations during the study at
Plant LC.
Data from the various plant studies on emission concentrations of
gross particulate matter, SC>2, total water soluble sulfates (SO"),
plume opacity, and in-stack opacity were reviewed. As much as possible,
data were selected for those periods of time when these measurements
were made concurrently. Tables 2, 3, and A are a consolidation of these
data. Table 2 summarizes the emission data for oil-fired power plants
without any emission control systems, Table 3, for coal-fired power
plants with ESP controls, and Table 4, for a coal-fired power plant with
2 stage wet scrubbers (particulate control plus flue &as desulfuriza-
tion, FGD). Various constraints such as number of available sampling
ports in a given location did not permit the desired measurements to be
executed concurrently at Plant LC and this is reflected in the data in
Table 4. These data represent sampling visits to this source on three
different dates.
Figure 2 graphically portrays the data of Table 2 showing the com-
parison of t!ie plurcc opacity data with the in-stack opacity data at the
oil-fired power plants. Figure 2 also provides data on the effect of
additional condensation on plume opacity with cooling of the plume down-
stream of the stack exit location.
55
-------
DISCUSSION
At the oil-fired power plants M and A (Table 2) the most distin-
guishing features are the vanadium content of the fuel oil, levels of
excess 02, and their impact on plume opacity. Plant M was burning
domestic fuel oil with about 15 ppm V and 1.2% S compared to Plant A
which was burning Venezuelan fuel oil with 590 ppm V and 2.4% S. Both
plants utilized fuel additives. A significant difference between plume
and stack opacity existed for both fuels and for different levels of
excess Q£.
The plume opacity at Plant A at normal operation was 31% at the
stack exic and above the opacity emission standard of 20%. The opacity
Increased markedly to 43% further downstream as more condensation of
sulfuric acid occurred with cooling of the plume. The observers tended
to read higher opacity values than the Lidar.
Both solid particulate matter and condensed sulfuric acid (liquid
droplets) affect opacity. Unfortunately, concurrent data are not com-
plete in Table 2, but qualitative data from acid emission measurements
in other studies' 910 reinforce some observations which can be made
from Table 2. The concentration of solid particulate matter increased
as excess Ofc for combustion was decreased to reduce acid formation.
We attribute this to unburned carbon soot particles which have been
observed in a related study11. The increase of in-stack opacity with
decrease in excess 02 demonstrates this. Since the acid is in the gas
phase in the stack, a decrease in acid with a decrease in excess 02 does
not affect the in-stack opacity data or the above interpretation of the
data. As a matter of fact, the possibility of reduced sulfate salts
exists with the decreased acid and this would tend to counteract the
effect of the unburned carbon. This would imply a greater impact of
acid on stack opacity than was actually observed.
In the plume, the acid (at temperatures below its dewpoint) appears
as liquid droplets after condensation. With increased excess 02, the
increased acid and sulfate salts tend to increase the plume opacity but
a counteracting effect is the concurrent reduction in unburned carbon
resulting from more complete combustion of the oil. Since the condensa-
tion of the acid is a function of the plume temperature, one can infer
56
-------
on a semi-quantitative basis the contribution of the condensed acid in
the plume opacity relative to that of the solid particulate (both
unburned carbon and sulfate salts) by a comparison of the plume opacity
at the exit to that downstream of the exit. At 0.22 02 the plume opa-
city increase was from 31 to 43%. At 0.6% 02 the increase was from 23
to 54X, indicating the presence of more acid at higher excess 02 levels.
The impact of the acid may actually be more than indicated because
dilution of the plume downstream can reduce the opacity and counteract
the effect of the increase in condensed acid.
It is of interest to note that there appears to be an increase
(56%) in particulate loading as determined by Method 5 with an increase
in excess 02 (Table 2, Plant A). One might expect a decrease because of
a reduction in unburned carbon with more complete combustion. There is
the possibility of an increase in measured particulate loading due to
the collection of the gaseous acid and sulfate salts by Method 5.
Related studies in our laboratory have shown the glass fiber filter to
be a good collector of the gaseous acid12. One can postulate that two
overlapping functions (one an increase in sulfate salts and acid and
another a decrease in unburned carbon with increasing excess 02) contri-
bute to the particulate loading. The former will be a curve with a
positive slope, the latter a curve with a negative slope. The resulting
curve on particulate loading as a function of excess 02 would have a
positive or negative slope depending upon which function has the steeper
slope. The resulting curve would approach a straight line (zero slope)
as the two functions tend to exactly counteract each other. Conse-
quently, depending upon the amount of excess 02, the particulate loading
may be on either the rising or declining slope of the curve or it may be
more or less constant.
The emission characterization data for high sulfur (>22 S) coal-
fired power plants with ESP controls show no significant difference
between plume and in-stack opacity under normal ESP operation or with
reduced electric fields in the ESP's. It is possible that the high ash
content of the coal and resulting high particulate loading in the emis-
sion have a predominant effect on the in-stack and plume opacity. In-
stack opacity at normal operation of the ESP was close to the opacity
emission standard for new sources and higher than that for the oil-fired
power plants. The ratio of SOi*" to particulate matter for the coal-
fired emissions is <1 and for the oil-fired emissions, >1.
The stack gas environment for the coal-fired power plant (LC) with
particulate and gas controls (two-stage wet-scrubber) was unlike that for
plants with ESP controls. The stack gas temperatures were below the
sulfuric acid dewpoint and the water vapor content from the wet scrubbers
was high. The result was that sulfuric acid will appear in the gas
stream as condensed acid droplets and these directly affect the in-stack
opacity.
Concurrent emission data could not be obtained for Plant LC
(Table 4) in the same manner that it was for Plants P and MC (Table 3)
57
-------
because the required number of sampling ports was not available. None-
theless, the data obtained from the three visits to Plant LC do permit
some qualitative observations. The emission data on the particulate
loading appear to fall within a narrow range of values indicating con-
sistent plant operation. The plume and in-stack opacity data show no
significant difference but the very high opacity values are not consis-
tent with the particulate loading, size, and composition normally
associated with fly ash emissions. Optical transmittance measurements
conducted at different wavelengths during the study gave data that
varied with wavelength in the visible portion of the spectrum13. This
variation with wavelengths is indicative of submicron size distribution.
The submicron size was also substantiated with in-stack impactor
measurements11*. The acid composition of the gas stream was substantiated
by the controlled condensation measurement data7. In this case, we
attribute the high in-stack opacity levels to fine particle concentra-
tion with a mass mean diameter in the submicron size range and with a
significant percentage of the composition consisting of condensed
sulfuric acid.
There are a number of important questions raised by the data .
obtained thus far. More studies are needed to adequately address these
questions and to determine the variation of these pollutant emissions
with operating parameters. The questions can be briefly stated as
follows:
0 What is the quantitative distribution of H^SOi, in the gas
stream between free acid and acid adsorbed on particulate
matter?
• What is the distribution of the sulfate ion (SOt*") between
acid and salts?
0 What is the size distribution of acid and salts?
There is need for more data on the physical properties of H^SOi* in both
the stack and plume environments to support proper interpretation of
optical data.
58
-------
SUMMARY
Emissions from oil-fired power plants without emission controls
«nd coal-fired power plants with ESP's and with FGD systems were charac-
terized for plume and in-stack opacity, S02, S0i»", and mass concentration.
Sulfuric acid content of the emissions from the oil-fired power plant
had a significant effect on the plurae opacity but no effect -on the
in-stack opacity. In the case of the coal-fired power plants with ESP's
the in-stack and plume opacities were essentially the same. This led to
the conclusion that the concentration of acid was low relative to the
non-acid particulate such that the acid did not contribute to any
significant degree to the opacity of the plume beyond that normally
associated with the fly ash. The in-stack and plume opacities of the
emissions for the high sulfur coal-fired power plant with the two-stage
wet scrubber system were comparable but significantly high (70 to 90%).
The high opacity was attributed mainly to the sulfuric acid content of
the emissions and to submicron size of the particulate matter.
59
-------
REFERENCES
1. U.S. Environmental Protection Agency, Standards of Performance for
New Sources. Fed Regist. 36, 24876-24895, 1971.
2. U.S. Environmental Protection Agency, Standards of Performance for
New Sources. Fed Regist. 40, 43850-43854, 1975.
3. Cook, C. S., G. W. Bethke, and W. D. Conner. Remote Measurement of
Smoke Plume Transmittance Using Lidar. Appl Opt. 11, 1742-1748,
1972.
4. Johnson, W. B., R. J. Allen, and W. E. Evans. Lidar Studies of
Stack Plume in Rural and Urban Environments. U.S. Environmental
Protection Agency, Research Triangle Park, N. C. Publication
Number EPA 650/4-73-002. 1973. 112 p.
5. Peterson, C. M., and M. Tomaides. In-Stack Transmissometer Tech-
niques for Measuring Opacities of Particulate Emissions from Sta-
tionary Sources. NTIS. Publication Number PB-212-741.
6. Herget, W. F., and W. D. Conner. Instrumental Sensing of Stationary
Source Emissions. Environ Sci and Technol. 11, 962-967, 1977.
7. Homolya, J. B. Unpublished data. U.S. Environmental Protection
Agency, Research Triangle Park, N. C. 1978.
8. Homolya, J. B., and J. L. Cheney. An Assessment of Sulfuric Acid
and Sulfate Emissions from the Combustion of Fossil Fuels. In:
Proceedings of Workshop on Measurement Technology and Characteriza-
tion of Primary Sulfate Emissions from Combustion Sources. Southern
Pines, N. C. April 24-26, 1978. J. S. Nader, Ed. EPA document in
press.
9. Dietz, R. N., and R. F. Wieser. Operating Parameters Affecting Sul-
fate Emissions from an Oil-Fired Power Unit. In: Proceedings of
Workshop on Measurement Technology and Characterization of Primary
Sulfate Emissions from Combustion Sources, Southern Pines, N. C.
April 24-26, 1978. J. S. Nader, Ed. EPA document in press.
60
-------
10. Cheney, J. L., and J. B. Homolya. Characterization of Combustion
Source Sulfate Emissions with a Selective Condensation Sampling
System. In: Proceedings of Workshop on Measurement Technology
and Characterization of Primary Sulfate Emissions from Combustion
Sources, Southern Pines, N. C. April 24-26, 1978. J. S. Nader,
Ed. EPA document in press.
11. Bennett, R. L., and K. T. Knapp. Chemical Characterization of
Particulate Emissions from Oil-Fired Power Plants. In: Energy
and the Environment, Proceedings of the Fourth National Conference,
Cincinnati, Ohio. October 3-7, 1976. P. 501-506. AICHE, Dayton,
Ohio, 1976. 594 p.
12. Cheney, J. L. Unpublished data. U.S. Environmental Protection
Agency, Research Triangle Park, N. C. 1978.
13. Conner, W. D. Unpublished data. U.S. Environmental Protection
Agency, Research Triangle Park, N. C. 1978.
14. Knapp, K. T. Unpublished data. U.S. Environmental Protection
Agency, Research Triangle Park, N. C. 1978.
61
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Table 1. SUMMARY OF PHYSICAL AND NORMAL OPERATING FEATURES
OF POWER PLANTS STUDIED
INJ
Plant
A
M
P
MC
LC
Fuel
Burned
Oil
Oil
Coal
Coal
Coal
Height
(m)
150
60
88
178
213
Stack
Diameter
(m)
6.8
3.
4.1
4.7
7.
Fuel Content
Tempera-
ture (°C)
160
127
154
166
77
Ash
M
0.17
0.07
8.
14.
30.
S
M
2.4
1.2
3.3
3.9
5.4
V
(ppm)
590
15
99
35
50
Excess
Boiler
0? (%)
0.2
3
5.
4.
3.8
Emission
Controls
only fuel
additives
only fuel
additives
ESP
ESP
2-stage
Power
Output
(KM)
525
190
100
330
820
wet scrubber
(particulate
plus FGD)
aAs measured at economizer outlet
-------
Table 2. EMISSION CHARACTERIZATION DATA FOR OIL-FIRED
POWER PLANTS WITHOUT ESP
PLANT M
CT>
CO
Date
8/10/76
8/19/76
8/19/76
8/17/76
8/19/76
8/19/76
Part.
2
Time (mg/Nm )
1115-1215 27
1125-1145
1145-1200
1145-1205 250
0945-1000 390
1000-1015 390
SOZ S04" S04"/SOX Plume In-Stacka
(mq/m3) (mg/m3) (%) Opac. (%) Opac. (%)
Lldar
1,600 68 4.1 10±2
PLANT A
3U4
43±3b
3,800 340 8.2 23±3
23±2
54±3b
Obs.
6±1
30±1
52±2b
42±1
37±2
61±2b
2-3
18-22
18-22
11-15
11-15
11-15
Remarks
15 ppm 1
590 ppm
590 ppm
590 ppm
590 ppm
590 ppm
aTransmissometer measurements.
Measurements about 3 stack diameters (15 meters) downstream of stack exit.
-------
Table 3. EMISSIONS CHARACTERIZATION DATA FOR COAL-FIRED
POWER PLANTS WITH ESP's
PLANT Pd
Date
7/19/77
7/20/77
7/22/77
7/26/77
7/27/77
7/28/77
7/28/77
Part.
Time jmg/Nm )
1551-1636
1020-1120
0939-1039
1430-1545
0915-1015
0900-1000
1110-1210
840
1,100
360
330
2,800
2,100
450
SO,
3
(mg/m )
7,200
6,000
7,300
5,900
5,900
6,500
6,500
(mg/m )
so4-/so
a8% Ash, 3.3% S, 99 ppm V, 100 MM
b!42 Ash, 3.9% S, 35 ppm V, 330 MW
C0bserver measurements
Transmissometer measurements
250
330
180
PLANT
210
190
240
240
3/4
5.2
2.4
MCb
3.4
3.1
3.6
3.6
Plume** In-Stack
Opacity (%) Opacity (%) Remarks
27
23
32
18
86
80
20
21
28
31
21
81
72
17
2 fields off
2 fields off
2 fields off
1 field off
3 fields off
3 fields off
Normal opera-
tion
-------
Table 4. EMISSIONS CHARACTERIZATION DATA FOR COAL-FIRED
POWER PLANT LC WITH FGDd
tn
Date
9/19/77
9/19/77
9/19/77
9/19/77
11/2/77
11/3/77
11/3/77
4/3/78
A/3/78
4/4/78
4/4/78
4/5/78
4/5/78
Time
1014-1121
1201-1309
1390-1500
1528-1635
1529-1629
1345-1445
1530-1630
1245-1345
1515-1615
1145-1245
1345-1445
0930-1030
1130-1230
Part.b S0~b
1 *J
(mg/NnT) (mg/nT)
2,000
3,100
4,200
5,500
240
270
350
320
220
280
260
280
SO/ SO//SO b Plumec
*\ *\ *r X
(mg/nn (%) Opacity (%)
190 8.7
260 7.7
170 3.9
170 3.0
75.
>90
>90
>90
>90
>90
>90
In-Stackd
Opacity (%)
59-67
62-71
62-71
>90
>90
>90
>90
>90
>90
a30% Ash, 5.42 S, 50-ppm V. 820 MW
Measurements made on one of 8 parallel FGD modules.
C0bserver Measurements
dTransmissometer measurements at stack breeching.
-------
Free 1I2S04 (Gas Phase)
Particles with Adsorbed H,S04 rrv '•'.'
Sulfate Particles
••/•-. Free i>02
Particles with Adsorbed SO
Stack Ducting
Figure 1. Sulfur Oxides Present in the Stack Gas Stream
-------
+*
c
o
u
(4
o
d
O
t*
•O
•H
J
3
i-H
A
50
40
30
20
10
^
• 1%S, 15 ppm V, 4*02
A '2.5%S, 590 ppm V, 0.2302
• 2.5%S, 590 ppm V, 0.6%02
Lidar Measurement
Location above Stack Exit
Unprimed - 2 to 3 meters
Primed - 15 meters
I I I
10 20 30 40 50
In-Stack Transciissometer Opacity, percent
Figure 2. Concurrent Plume and In-Stack Opacity Data
for Emissions from Oil-Fired Power Plants
67
-------
Charts Showing In«Stack Opacity Measurements and Individual
Opacity Readings of Participants fn Collaborative Testing of
EPA Method 9. [Data taken from tables In EPA Report No. 650/4-
75-009, Evaluation and Collaborative Study of Method for Visual
Determination of Opacity of Emissions from Stationary Sources,
H. Hamll, January 1975)
69
-------
AFTER HAMIL AND THOMAS
EPA-650/4-75-009
JANUARY 1975
10 15 20 25
TRANSMISSOMETER OPACITY, percent
BLACK SMOKE GENERATOR
VIEWING CONDITIONS: IDEAL
TOTAL NO. OF POINTS: 132
NO. OF DETERMINATIONS PER OBSERVER: APPROXIMATELY 16
-------
35
30
25
I
I20
<
> 15
cc
LLJ
v»
CO
o
10
X
AFTER HAMIL AND THOMAS
EPA-65Q/4-75-OQ9
JANUARY 1975
O MULTI-POINT
0 5 10 15 20 25
TRANSMISSOMETER OPACITY, percent
WHITE SMOKE GENERATOR
VIEWING CONDITIONS: IDEAL, BLUE SKY, BRIGHT SUNSHINE
TOTAL NO. OF POINTS: 170
NO. OF DETERMINATIONS PER OBSERVER: APPROXIMATELY 20
30
35
73
-------
30
25
20
0.
o
QC
GC
UJ
CO
CO
0
15
10
AFTER HAMIL AND THOMAS
EPA-650/4-75-009
JANUARY 1975
10 15 20
TRANSMISSOMETER OPACITY, percent
25
30
RIVERBEND STEAM STATION TEST NO. 1
VIEWING CONDITIONS: CLOUDY. LOW HAZE
TOTAL NO. OF POINTS: 45
NUMBER OF DETERMINATIONS PER OBSERVER: 19
1C
I w
-------
AFTER HAMIL AND THOMAS
EPA-650/4-75-009
JANUARY 1975
v-: x
10 15 20
TRANSMISSOMETER OPACITY, percent
RIVERBENO STEAM STATION TEST NO. 2
VIEWING CONDITIONS: MARGINAL, SOLID OVERCAST
TOTAL NO. OF POINTS: 85
NO. OF DETERMINATIONS PER OBSERVER: 17
77
-------
so
40
30
a.
o
OC
20
CO
o
10
AFTER HAMIL AND THOMAS
EPA-650/4-75-009
JANUARY 1975
O MULTI-POINT
10
20
30
40
TRANSMISSOMETER OPACITY, ptrcent
RIVERBENO STEAM STATION TEST NO. 3
VIEWING CONDITIONS: IDEAL. CLOUDLESS. BRIGHT SUNSHINE
TOTAL NO. OF POINTS: 96
NO. OF DETERMINATIONS PER OBSERVER: 24
50
79
-------
30
25
20
<
a.
o
cc
cc
LU
v>
CO
o
10
1 I I
NUMBERS-;* DETERMINATIONS AT POINT
* *^ / *
•3 v»* •¥ •
•3,»12»6
18/t*2«27«IO.tO
•12*3
10 15 20
TRANSMISSOMETER OPACITY, percent
STAUFFER CHEMICAL (ACID MIST PLUME)
VIEWING CONDITIONS: GOOD. BLUE SKY. LIGHT HAZE
TOTAL NO. OF POINTS: 297
NO. OF DETERMINATIONS PER OBSERVER: APPROXIMATELY 30
25
30
81
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