STUDENTS MANUAL
EVALUATION OF
VISIBLE EMISSIONS
vtai Protection Agency
lution Control Office
ite for Air Pollution Training
Contract No, CPA 70-175
ir
llBatteiie
Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
Telephone (614) 299-3151
Telex 24-5454
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STUDENT'S MANUAL
for
EVALUATION OF VISIBLE EMISSIONS FOR
STATE AND LOCAL AIR POLLUTION INSPECTORS
August, 1971
Edited by
Philip R. Sticksel and the Staff of
BATTELLE
Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
Franklin County
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FOREWORD
This Student's Manual for the Evaluation of Visible Emissions Course
is divided into two parts, A and B. The purpose of this manual is
to aid both the student and the instructor to achieve the course ob-
jectives in an efficient manner. It is expected that the instructors
for the course will draw heavily upon the articles in Part A when
preparing their course lectures. With this knowledge in mind it is
suggested that the student may use Part A to preview, follow, or re-
view the course lectures.
The material in Part A has been compiled from several sources. Much
of it has come from articles published in the manual for the Institute
for Air Pollution Training's Course 439, Visible Emissions Evaluation.
Additional material was taken from various publications including
several by the Office of Air Programs of the Environmental Protection
Agency. However, the key ingredient in putting together the present
manual, specifically directed toward training visible emissions in-
spectors, has been the lecture notes from the staff and guest instruc-
tors who have been teaching in Course 439 since its inception in 1968.
Part B is an editing and revision of material taken from the Course
439 manual and from several articles used as handouts. The purpose
of Part B is to give the student and the instructor additional in-
formation about the topics in Part A.
At the end of each article in Part A there is a short list of refer-
ences to Part B articles and to other material which should be
easily available to the air pollution control specialist from his
office library.
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ACKNOWLEDGEMENTS
As mentioned in the Foreword, considerable use has been made of the
lecture notes of the instructors for Course 439. Since much of their
material has not been published previously, the editor acknowledges
here the debt that the present manual owes to the preparation by
these staff and guest instructors. Included in this list are:
Ron Aubert, Attorney
Larwin Company
Beverly Hills, California
William Axtman
American Boiler Manufacturing
Association
Newark, New Jersey
Hilton Bradley, Attorney
Gary, Indiana
Larry Curtis, Attorney
Los Angeles County Counsel Office
Los Angeles, California
Dennis Holzschuh
Institute for Air Pollution
Training, EPA
Research Triangle Park
North Carolina
Mike Magoulas
Todd Products
Houston, Texas
C. Richard Pelley
Ayrshire Coal Company
Indianapolis, Indiana
Joe W. Riley
Regional Office, EPA
Atlanta, Georgia
Jerome Rom
Office of Air Programs, EPA
Durham, North Carolina
Frank Scott
Maryland State Department
of Health
Baltimore, Maryland
Matthew Walker
District Counsel
Bay Area Air Pollution
Control District
San Francisco, California
Many other fine lecturers have given time and effort to this course;
however, the editor has drawn especially from the preparation of the
above men.
For helping him in formulating the guidelines, objectives, format,
and examination for this course, the editor wishes to thank the
following people: Tommie Gibbs and William Todd of EPA, Tom Rinkoski
of the Ford Motor Company, and Ann H. Sticksel.
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STUDENT'S MANUAL
TABLE OF CONTENTS
PART A - KEY POINTS
I. VISIBLE EMISSIONS, THEIR CAUSE AND REGULATION A-l
II. PRINCIPLES OF COMBUSTION A-3
Movie: "The 3 T's of Combustion" A-4
III. COMBUSTION OF FUEL OIL - CORRECT PRACTICES A-6
Classification of Fuel Oil A-6
Oil Burner Types A -6
Boiler Types A -8
Soot Blowing A -8
Black Smoke and White Smoke A-9
Participates A-9
Sulfur Trioxide A -9
Control Equipment . A-10
IV. COMBUSTION OF COAL AND ITS CONTROL A-11
Classification of Coal A -11
Basics of Coal Combustion and Combustion Equipment A -12
Some Terms Used in Coal Combustion A-13
Plume Visibility A-14
Mechanical Coal Firing Equipment A-15
Causes and Control of Paniculate Emission From Coal Combustion A -16
V. OTHER COMBUSTION EMISSIONS: INCINERATORS, AGRICULTURAL
BURNING, NATURAL GAS, AND MOBILE SOURCES A-18
Solid Waste Disposal by Incineration A-18
Agricultural Burning A-20
Combustion of Natural Gas A -20
Engines Used in Transportation A -21
Visible Emissions From Mobile Sources A -22
VI. NONCOMBUSTION EMISSIONS AND WATER VAPOR PLUMES A-25
Furnaces A-25
Driers A-26
Terminology in Metallurgical Processing A-26
Iron and Steel Mills A -27
Gray Iron Foundries A -28
Non-Ferrous Metallurgical Industry A-28
Petroleum Refineries A -29
Portland Cement and Lime Plants A-30
Kraft Pulp Mills A -30
Sulfuric Acid Manufacturing A -31
Nitric Acid Plants A-32
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TABLE OF CONTENTS
(Continued)
Page
Paint and Varnish Manufacturing A-32
Hot-Mix Asphalt Batching Plants A-32
Phosphoric Acid Manufacture A-33
Phosphate Fertilizer Manufacture A -33
Soap and Synthetic Detergent Manufacture A -34
Wet Plumes A -34
VII. CLASSIFICATION AND IDENTIFICATION OF SOURCES A -37
Identification A-37
VIII. RINGELMANN CHART AND EQUIVALENT OPACITY A-40
The Ringelmann Chart A-41
Smoke Reading Aids A-41
Training of Inspectors A -42
Problems of Reading Smoke in the Field A -43
Advantages of Visible Emission Regulations A-44
IX. QUALIFICATION PROCEDURES AND EXERCISE IN RECORDING FOR QUALIFICATION .... A -45
Instructions to the Student During the Reading of Smoke A-45
Filling Out the Training Form A -45
X. BASIC METEOROLOGY A-48
Radiation, Stability, and Inversions A-48
Weather Maps A-49
Particles in the Air and Obstruction to Visibility A-50
Clouds and Fog A-50
Eddies and Turbulence A-50
XI. METEOROLOGICAL FACTORS IN SMOKE READING . . . A-52
Effects on Readings of Plume Density A-52
Atmospheric Humidity and Water Vapor Plumes A-52
Useful Information That a Smoke Inspector Can Obtain From the Daily Weather Map. . . A-52
Weather Observations to be Made by the Smoke Reader A-53
XII. LEGAL ASPECTS OF VISIBLE EMISSIONS A-55
History and Test Cases A-55
Equivalent Opacity and Smoke Emission Laws A-56
Local Regulations A-56
How to be an Expert Witness A-56
XIII. OBSERVATION REPORTS FOR VIOLATIONS A-59
Special Designations A-59
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TABLE OF CONTENTS
(Continued)
XIV. EMISSION GENERATOR A-60
Mark II Smoke Generator A-60
Black Smoke A-60
White Smoke A-60
Transmissometer A-60
Conduct of the School A-61
Other Smoke Generating Equipment A-61
PART B - SUPPLEMENTAL READINGS
CLASSIFICATION OF SOURCES OF EMISSION B -1
C. A. Lindstrom
BASIC COMBUSTION CONCEPTS B-9
Darryl J. von Lehmden
FACTS ABOUT FUELS B-15
L. N. Rowley, J. C. McCabe and B. G. A. Skrotzki
OIL BURNING EQUIPMENT B-21
L. N. Rowley, J. C. McCabe and B. G. A. Skrotzki
COAL BURNING EQUIPMENT B-2T
W. S. Smith and C. W. Gruber
DESIGN OF COAL COMBUSTION EQUIPMENT B-31
F. S. Scott
COAL BURNING - DESIGN PARAMETERS . .- B-39
U. B. Yeager
COAL BURNING - GOOD OPERATIONAL PRACTICES B-53
U. B. Yeager
TERMINOLOGY USED IN INCINERATOR TECHNOLOGY B-59
CLASSIFICATION OF INCINERATORS B-63
DESIGN PARAMETERS FOR 1.1. A. INCINERATOR CLASSES IIA, III, IV, VI AND VII B-65
R. Coder
OPERATION PRACTICES FOR 1.1. A. INCINERATOR CLASSES IA, IIA, III, IV AND VII B-69
R. Coder
FLARE COMBUSTION B-71
Leonard C. Mandell
CONTROL EQUIPMENT FOR INDUSTRIAL PARTICULATE EMISSIONS B-75
T. L. Stumph
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TABLE OF CONTENTS
(Continued)
Page
INDUSTRIAL PROCESSES WHICH DISCHARGE PARTICULATE EMISSIONS B-19
OPACITY PROBLEMS CAUSED BY WATER VAPOR B-89
Frank L. Cross, Jr. , and Philip R. Sticksel
STANDARDS FOR PARTICULATE EMISSIONS B-95
C. A. Lindstrom
METEOROLOGIC FUNDAMENTALS B-103
D. B. Turner
EFFECTS OF METEOROLOGIC PARAMETERS ON TRANSPORT AND DIFFUSION B-lll
D. B. Turner
POLLUTANT CONCENTRATION VARIATION B-115
D. B. Turner
LEGAL ASPECTS OF AIR POLLUTION B-119
H. C. Crowe
TECHNIQUES FOR VISUAL DETERMINATION B-123
D. P. Holzschuh
READING VISIBLE EMISSION B-12T
Jerome J. Rom
EQUIVALENT OPACITY B-13T
INDEX 1
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COURSE OBJECTIVES
At the conclusion of this course the student should be able to:
(1) Visually measure (i.e., without the use of devices) the shade of visible air pollution
emissions:
(a) Maintaining an average deviation
from the correct reading of less
than 7.5 percent for a set of
25 shades of white smoke
and 25 shades of black
smoke
(b) Not have any of his readings
deviate from the correct read-
ing by 20 percent (one whole
Ringelmann) or more.
(2) Define Ringelman Number and Equivalent Opacity in the following manner:
(a) The Ringelmann Number gives shades
of gray by which the density of
columns of smoke rising from some
source may be compared. It is a
system whereby graduated shades of
gray, varying by five equal steps
between white and black, may be
accurately reproduced by means of
a rectangular grill or by black
lines of definite width and spacing
on a white background
(b) Equivalent Opacity is an extension
of the Ringelmann Chart by limiting
such visible emissions not only to
a shade of gray, but to such opaci-
ties as to obscure an observer's
view to a degree equal to or greater
than does smoke of Ringelmann No. 2
shade. Thus No. 2 = 40 percent
opacity.
(3) List the following essential conditions for correctly evaluating the plume:
(a) Keep the sun at your back
(b) Try to have a contrasting background
(c) Readings should be taken at right angles
to wind direction and at any distance to
obtain a clear view
(d) Readings should be made through the most
dense part of the plume and where plume
is no wider than diameter of the stack.
(4) List the following essential items to be recorded on the training form:
(a) Name (d) Wind speed
(b) Date (e) Wind direction
(c) Time (f) Sky condition
and properly fill out these items for his field recording form.
(5) List at least four of the following techniques for measuring visible emission without
the aid of references:
(a) Smoke guide
(b) Umbrascope
(c) Photo-electric (f) Sight reading
cell
(d) Smokescope
(e) Smoke tintometer
(6) Differentiate between the plumes emitted from combustion processes and industrial processes.
(7) Identify water vapor plumes.
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COURSE OBJECTIVES (Continued)
(8) Make application of his knowledge of meteorology in the following manner:
.(a) Estimate wind speeds from 0-18
mph using the Beaufort Scale
(b) Define wind direction and esti-
mate wind direction
(c) Estimate sky condition (percent-
age of cloud cover)
(d) List the distinguishing character-
istics of high and low pressure
(e) Identify on a weather map the
symbols for the following:
high pressure area
low pressure area
cold front
warm front
occluded front
stationary front
(f) List at least two points of infor-
mation obtained from a weather map
which the smoke inspector could find
useful in planning his activities.
(9) Testify in court as an effective expert witness concerning visible emission observations.
To demonstrate his capability he should be able to:
(a) Idenitfy 8 of the 10 criteria for
being an expert witness
(b) List 5 of the 8 rules for behavior
on the witness stand
(c) Cite the legal precedents set in
the California appeal cases con-
cerning visible emission regulations.
(10) State the essential elements of his local or state visible emission code.
(11) List the primary components of the emission generator:
(a) Combustion chamber for generating
black smoke
(b) Generator's exhaust manifold for
white smoke
(c) Transmissometer
(d) Auxiliary blower
(e) Recorder or indicator.
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30
PART A - KEY POINTS
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I. VISIBLE EMISSIONS - THEIR CAUSE AND REGULATION
1.1. Visible emissions are composed of
small liquid particles, or colored gases.
1.2. The more opaque a plume is, the more
effluent is being emitted, all other parti-
culate and flow characteristics being equal.
The more effluent emitted, the poorer the
air quality.
1.3. Some air pollutants are invisible
or colorless gases or are composed of par-
ticles so small that they cannot be detected
by the naked eye, e.g., S02, lead, CO.
1.4. The micron (y,) is a measurement of
length used to measure particle diameters.
It is equal to .001 (one thousandth) of a
millimeter.
1.5. Particles between 0.3 and 100 p, are
measured as suspended particulate by high-
volume samplers.
1.6. Particles between 0.1 and 1.0 p,
cause haze: They cause the sunlight to
scatter in the visible wavelengths (0.4 to
0.7 p,) of light. Larger particles are
visible because they intercept or reflect
the sunlight. Smaller particles have
little effect on the light and are in-
visible.
1.7. Visible air contaminants can be
classified as
(a) Smoke
(b) Soot
(c) Fly ash
(d) Dust
(e) Fumes
(f) Mist
(g) Gas
(h) Vapor
1.8. Plumes of condensed water vapor
are visible, but uncombined water is gene-
rally not considered a pollutant.
1.9. Smoke is a visible effluent re-
sulting from incomplete combustion and
consisting mostly of soot, fly ash, and
other solid or liquid particles less than
1 p, in diameter.
1.10. Soot is a cluster of carbon par-
ticles saturated with tar. It is formed
by the incomplete combustion of carbon-
containing material. It is the principal
cause of the blackness of a smoke plume.
1.11. Fly ash is unburned material
arising from the combustion of fuel. It
has sufficiently small size that it can
remain suspended in the air. A pure fly
ash plume will be of a light-brown or
cream color.
1.12. Fumes consist of metal or metal
oxide particles less than 1 p. in diameter.
The particles are formed when the metal is
heated to its boiling point and some of it is
changed to a gaseous state. When the gas
cools, small particles (the fume) are formed.
1.13. Dust consists of solid particles,
generally greater than 1 p, in diameter, re-
leased to the air by processes such as
crushing, grinding, drilling, sweeping,
sanding, demolishing, etc. Since they are
larger than the smoke or fume particles,
they will settle to the ground faster.
1.14. Mist consists of liquid particles
or droplets which are not composed of pure
pollutant but contain it in solution or sus-
pension. The droplets are of the size of fog
droplets (about 10 p, - ranging from 2 to 200
P.).
1.15. Gas is fluid such as air which has
neither independent shape or volume but tends
to expand indefinitely. Two visible pollutant
gases are nitrogen dioxide (N02), which is
brown to yellow, and chlorine, which is green-
ish yellow.
1.16. Vapor is the gaseous phase of a sub-
stance which at normal temperature and pres-
sure is a liquid or solid, e.g., vapor from
gasoline.
1.17. Most visible plumes are composed of
particulates. The reasons for particulates
being objectionable are their effects on
(a) Materials (d) Health
(b) Visibility (e) Vegetation
(c) Incoming sunlight
The effects of Items (a) through (e) are dis-
cussed in 1.18 through 1.22.
1.18. Materials. Particulates deposited on
clothes, automobiles, or houses must be washed
off. When particulates are accompanied by
sulfur dioxide and moisture, the rate of cor-
rosion increases.
1.19. Visibility. Particulates in the air
reduce the distance that one can see. If this
visual range is decreased enough, it can cause
unsafe operation of vehicles.
1.20. Incoming sunlight. Particulate mat-
ter in the air can cause the sun's ray to be
reflected or scattered, reducing the heat and
light reaching the earth's surface.
1.21. Health. Increases in respiratory
illness and even deaths may occur from high
particulate concentrations, especially when
sulfur dioxide concentrations are also high.
Bronchitis patients will experience symptoms;
particles less than 5 p, in diameter can reach
the lungs.
A-l
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Visible Emissions
1.22. Vegetation. Cement dust can reduce
vegetation growth and cause its damage. Flu-
oride dust in the presence of water can damage
leaves. If the fluoride dust is deposited on
plants that are eaten by animals, the animals
can contract fluorotic poisoning.
1.23. Regulations for restricting particu-
late emissions are in common use. The regu-
lations are typed by
(a) Weight concentration, which
states the limit in relation
to amount of flue gas emitted;
e.g., 0.85 Ib of particulates/
1000 Ib of flue gas; 0.45
grains/std cu ft of flue gas
at atmospheric pressure and
60 F.
(b) Grain loading and process
weight, which states the
limit in relation to the
amount of material pro-
cessed, e.g., 12 Ib/hr of
particulate for 10,000 Ib/hr
of process weight.
(c) Limitation on basis of thermal
input in terms of British thermal
units (Btu). Example: For coal-
fired boilers of less than 10
million Btu/hr heat input, the
emission of fly ash and other
particulate matter shall not
exceed 0.6 pound of particulate
matter/million Btu.
(d) Boundary-line measurements of
ambient air quality. Example:
The suspended particulate out-
side the factory fence shall
not exceed a 24-hour average of
200 micrograms/m3.
(e) Plume shade density or opacity
in terms of Ringelmann Number
or its extension to Equivalent
Opacity. Example: No emission
as dark or darker than that de-
signated as No. 2 on the Ringel-
mann Chart is allowed for a total
of 3 minutes in 1 hour.
1.24. The regulation using the Ringelmann
Chart and Equivalent Opacity is the least time
consuming and the least expensive for the air
pollution officer.
Suggested Additional Reading
Part B*
Equivalent Opacity.
Other
"Effect on the Physical Proper-
ties of the Atmosphere", E. Robin-
son, Air Pollution Vol. _1, edited
by A. C. Stern, 1968.
*Llstings under Part B refer to article
titles in Part B of this manual.
A-2
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II. PRINCIPLES OF COMBUSTION
2.1. Combustion or burning is the rapid
oxidation of a fuel. This chemical reaction
between the fuel and oxygen requires a high
temperature.
2.2. Most common fuels contain carbon and
hydrogen plus sulfur and ash materials. The
ash does not burn, but the carbon, hydrogen,
and sulfur each combine with oxygen and pro-
duce heat and waste gases.
2.3. Two parts hydrogen plus one part oxy-
gen equals two parts water vapor:
two parts carbon monoxide:
2C + 0,
2CO
2H-
2H20
A pound of pure hydrogen will release 62,028
Btu (British thermal units) of heat when it
burns.
2.4. One part carbon plus one part oxy-
gen equals one part carbon dioxide:
C + 02 C02
A pound of pure carbon will release 14,544
Btu when it burns.
2.5. One part sulfur plus one part oxy-
gen equals one part sulfur dioxide:
0,
SO,
L*o D\Jn
A pound of pure sulfur will release 4,050 Btu
when it burns. The sulfur therefore produces
little heat but does produce a major air pol-
lutant.
2.6. In practice, combustion does not in-
volve pure hydrogen, carbon, sulfur, or oxy-
gen: oxygen is mixed with nitrogen in the
air; in fuel, the hydrogen is compounded with
the carbon to form complex tars, resins, etc.;
the sulfur is combined with other compounds or
with elements such as iron.
2.7. Thus, to make sure in practice that
all the carbon and hydrogen combine with oxy-
gen, three conditions must be maintained in
the furnacethe "three T's of combustion":
(a) Sufficient time for the mole-
cules of oxygen to come into
contact with the molecules of
fuel.
(b) An adequately high temperature
to sustain the reaction.
(c) Turbulence or mixing to make
sure that all the molecules
of fuel are combined with the
oxygen in the air.
2.8. One result which will occur if the
"three T's" are not sufficient is that car-
bon monoxide will be formed, since insuffi-
cient oxygen will combine with the fuel--
two parts carbon plus one part oxygen equals
2.9. Even with the "three T's", furnaces
are generally not so efficient as to insure
that every molecule of hydrogen and carbon
will be combined with a molecule of oxygen.
One remedy for this is to use more oxygen
than is theoretically necessary. This extra
oxygen is supplied by using excess air. How-
ever, there is a penalty for using this excess
air, since some of it becomes heated and goes
out the stack as part of the flue gas. This
heat used to raise the temperature of the ex-
cess air is wasted.
2.10. Methods used to increase the effect
of the "three T's of combustion" in furnaces
which are listed below include the following:
2.11. Temperature
(a) Heat the air before it
enters the furnace.
(b) Insulate the combustion
chamber of the furnace.
2.12. Turbulence
(a) Put baffles in the com-
bustion chamber.
(b) Introduce jets of air
which stir up the air
within the furnace as
well as adding more air.
2.13. Time
(a) Use baffles that also
cause the fuel and air
to remain in the com-
bustion chamber longer.
(b) Build the combustion
chamber large enough so
that the fuel and air
will remain inside long
enough for the combustion
to be completed.
2.14. If some of the fuel does not receive
enough air or temperature to burn all the car-
bon, the ash will contain some pieces of par-
tially burned or unburned carbon. When these
particles are deposited on something, the de-
posit is called soot. When the particles re-
main in suspension in the flue gas, they form
a black cloud called smoke.
2.15. If a furnace produces smoke, either
the fuel and air are not in balance or the
"three T's of combustion" are not being satis-
fied. One should look for one or more of the
following conditions:
A-3
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Principles of Combustion
(a) Insufficient air for the
amount of fuel
(b) Too much air, which chills
the flame before combustion
is complete
(c) Insufficient turbulence of
the air through the fuel
(d) Cold furnace when the fire
is first lit or is burning
at a low loadthis is often
accompanied by excessive air
leaking into the furnace
through doors and other holes.
2.16. All fuels or combustible materials,
whether solid, liquid, or gas, are burned as
a gas. Before it will burn, a solid or liquid
must be heated until it is transformed into
the gaseous or vapor state.
Movie; "The Three T's of Combustion
2.17. Several components of the kerosene
lamp are analogous to the components of other
combustion units, whether they be coal- or
oil-burning furnaces, incinerators, internal
combustion engines, or other devices. The ne-
cessity for time, temperature, turbulence, and
oxygen is universal among all combustion de-
vices.
2.18. The parts of a kerosene lamp include
(a) The glass container at the base
of the lamp where the kerosene
is stored; this corresponds to
a coal bunker or fuel tank.
(b) The wick through which the kero-
sene is transferred from the
storage to the burning area;
this is similar to a coal sto-
ker or a fuel line and fuel pump.
(c) The grate where the fuel is burned.
(d) The tuyere or diffuser above the
top of the wick; the tuyere breaks
up the fuel for better mixing
with the air. Its function re-
sembles that of an atomizer in
a fuel burner, an injection nozzle
in a diesel engine, or a carbure-
tor in a gasoline engine.
(e) The lamp chimney, which serves
as an enclosed area in which the
combustion can take place and also
as an outlet for the exhaust gases.
The combustion area corresponds
to the combustion chamber of a
coal furnace or jet engine and to
the cylinder of an automobile.
The exhaust portion is similar to
a smoke stack or a tail pipe.
2.19. There are several examples given in
the film which emphasize that incomplete com-
bustion will occur if any one of the "three
T's of combustion" is lacking.
2.20. Without the tuyere to diffuse the
fuel, there is a smoky fire because the drops
of fuel cannot be intermixed with a suffi-
cient amount of air for complete combustion.
2.21. Even with the tuyere the flame re-
mains smoky, because the cool ambient air re-
duces the temperature of the kerosene-air
mixture below the combustion temperature.
When the chimney is placed on the lamp, the
air can enter the lamp only below the tuyere.
The fuel and air above the tuyere can circu-
late around in the wide part of the lamp
chimney thus remaining at a high temperature
for a time sufficient for complete combustion.
2.22. At first, the lamp chimney glass is
cold and it cools the fuel-air mixture, caus-
ing a smoky flame. As the chimney warms up,
the glass radiates heat back to the air-fuel
mixture within and maintains the combustion
temperature. The design of the interior of
furnaces and the choice of refractory mate-
rial to line the walls are directed toward
reflecting the heat of combustion on parti-
cular zones or areas within the furnace.
2.23. If there is too much air for the
amount of fuel, then some of the heat is used
to warm the excess air and is wasted. The
temperature of the gas leaving the combustion
area is reduced.
2.24. If there is insufficient air for the
amount of fuel, the temperature of the ex-
haust gases will rise but there will be a
dense cloud of black smoke. This indicates
that fuel is being wasted. A diesel engine
can be adjusted to give more power by using
excess fuel, although with the detriment of
creating a black plume.
2.25. The film mentions two other ways of
increasing the amount of air and eliminating
smoky conditions besides controlling the
amount of air entering the lamp below the
flame:
(a) Building a higher chimney so
that the air pressure from the
bottom to the top of the lamp
chimney is increased. This
increased draft pulls air into
the combustion chamber at a
greater rate.
(b) Raising the bottom of the lamp
chimney above its base, allow-
ing air to enter above the grate.
This additional overfire air
eliminates the smoky flame, but
A-4
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Principles of Combustion
it also cools the flame causing
it to flutter and have a smoky
tip.
Part B
Suggested Additional Reading
Basic combustion Concepts.
Other
"Stationary Combustion Sources",
R. B. Engdahl, Air Pollution Vol.
edited by A. C. Stern, 1968.
A-5
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III. COMBUSTION OF FUEL OIL - CORRECT PRACTICES
Classification of Fuel Oil
3.1. The crude oil that is pumped out of
oil wells consists of 83 to 87 percent carbon
and 10 to 14 percent hydrogen combined as
hydrocarbons. It also contains traces of
oxygen, nitrogen, and sulfur.
3.2. The crude oil is refined; this con-
sists of separating and recombing the hydro-
carbons of the crude oil into gasoline, fuel
oil, etc. The refining process includes
distillation and, often, cracking.
3.3. By boiling the crude oil, distilla-
tion separates the hydrocarbons into groups
or "fractions" which have the same range of
boiling points. The fractions also vary in
density.
3.4. The lighter fractions, such as naph-
tha, gasoline, kerosene, and gas oil, are
called the distillates. The heavier fra-
ctions include asphalt and the heavy fuel
oils, which are called residuals. During
distillation, the sulfur-bearing compounds
and the ash originally present in the crude
oil are concentrated in the residual frac-
tions.
3.5. Products of simple distillation are
called straight run. Additional yield of
gasoline can be obtained by cracking the
heavier fractions.
3.6. Cracking consists of changing the hy-
drocarbon structure of the oil. This is done
by decomposing the oil through the applica-
tion of heat and pressure with or without a
catalyst. The resulting products then are
distilled again into heavy and light fractions.
3.7. There are five grades of oil used as
fuel oil, labeled as Numbers 1, 2, 4, 5, and
6. Number 6 is often called Bunker C. There
no longer is a Number 3 oil.
3.8. Numbers 1 and 2 are distillate fuel
oils generally used for home oil furnaces and
hot-water heaters.
3.9. Numbers 4, 5, and 6 are residual fuel
oils. Both Number 4 and Number 5 are used in
commercial establishments, large apartments,
and industrial plants. Bunker C (Number 6)
is used in ocean-going ships, power generation
plants, and larger commercial and industrial
burners which use over 50 gallons of oil per
hour.
3.10. Each of these oils has a set of stan-
dard specifications which distinguish it from
the other oils. These specifications may in-
clude flash-point temperature, water and se-
diment percentage, gravity, ash content, vis-
cosity, and others.
3.11. The viscosity and the ash and sul-
fur contents are the major characteristics
that affect air pollutant emissions.
3.12. The relative ease or difficulty with
which an oil flows is its viscosity. It is
measured by the time in seconds a standard
amount of oil takes to flow through a stan-
dard orifice at a standard temperature (100°F
or 122°F).
3.13. Viscosity indicates how oil behaves
when it is pumped and shows when it must be
preheated for handling. Numbers 5 and 6 fuel
oils are high viscosity oils and require pre-
heating facilities.
3.14. The sulfur content of fuel oil may
vary from a trace to 5 percent while the ash
may be as high as 0.3 percent by weight. The
distillate fuel oils are limited by specifi-
cation to less than one percent sulfur and
Numbers 4 and 5 fuel oil are limited to more
than 0.1 percent ash.
3.15. The sulfur content of the residual
fuel oil grades can be reduced by desulfuri-
zation processes or by blending low sulfur
African oils with the higher sulfur domestic
oils.
3.16. Crude oil contains thousands of hy-
drocarbon compounds which are classified as
paraffins, naphthene, aromatics, resins, and
asphalt.
3.17. If an oil is high in paraffins, the
temperature of the flame will cause them to
decompose into lighter and more volatile
fractions which burn easily.
3.18. Aromatics do not readily decompose,
but at temperatures at which they do, crack-
ing will occur which can produce tar, smoke,
and soot.
3.19. The olefins may crack and form com-
pounds which are hard to burn.
Oil Burner Types
3.20. The principal types of oil burners
which have been developed demonstrate a capa-
bility of coping with many possible variations
in oils.
3.21. Oil burners do not burn oil. They
proportion the air and oil and mix them in
preparation for burning.
A-6
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Combustion of Fuel Oil
3.22. Since all fuels burn as a vapor, the
liquid oil must either be converted to a gas
in the burner (vaporized) or divided into such
small particles or droplets (atomized) that
heat within the combustion zone of the furnace
will vaporize the fuel during its residence
time in the combustion chamber of the furnace.
3.23. If the temperature of flame in the
combustion chamber is too low, incomplete
combustion and smoke emission will result.
Cooling of the flame can occur when the com-
bustion chamber is too small or too large.
3.24. Oil burns like an onion peel, so it
is necessary for turbulence to provide suffi-
cient air to complete the combustion of each
successive layer. Consequently, it is im-
portant to mix the air and oil.
3.25. Vaporizing burners gasify the oil by
heating it within the burner. These burners
are limited in the range of fuels they can
handle and are used only for some residential
furnaces and water heaters.
3.26. Atomizing of fuel oil can be accom-
plished in three ways:
(a) Using steam or air under
pressure to break the oil
into droplets
(b) Forcing oil under pressure
through a nozzle
(c) Tearing the oil film into
drops by centrifugal force.
All three methods are used in burners.
3.27. With high-pressure steam- or air-
atomizing burners, the steam or air is used
to break up the fuel-oil stream at the burner
tip. The auxiliary fluid, moving at high ve-
locity, atomizes the slower moving oil stream
as the mixture is emitted in the furnace.
The combustion air is introduced through re-
gisters around each burner. When steam is
used, it prevents the entering-oil tempera-
ture from dropping. This aids the flow of
high-viscosity oil and improves atomizing
characteristics.
3.28. Oil-pressure atomizing burners de-
pend on high fuel pressure to cause the oil
to break up into small droplets upon passing
through the orifice.
3.29. Rotary-cup burners provide atomiza-
tion by centrifugally throwing the fuel from
a rotating cup or plate. These burners can
be divided into two classes--horizontal ro-
tary and vertical rotary. The vertical ro-
tary is used only for domestic burners (under
10 gallons per hour).
3.30. Horizontal rotary cup burners are
used for the residual fuel oils. The oil is
distributed on the cup or plate in a thin
film. The primary air from the burner fan is
discharged through an air nozzle which has
vanes to give the air a rotary motion opposite
that of the oil. Additional air for combus-
tion--secondary air--must also be injected
into the combustion chamber for complete bur-
ning.
3.31. Mechanical atomizing burners employ
both high oil pressure and centrifugal action.
The fuel oil is given a strong whirling action
before it is released into the orifice. These
are the burners most often found at large
steam power plants.
3.32. The key to optimum oil burner opera-
tion is careful control of fuel viscosity. A
given burner functions properly only if the
viscosity at the burner orifice is held be-
tween narrow limits.
3.33. If the viscosity is too high, effec-
tive atomization does not take place. If the
viscosity is too low, oil flow through the
orifice is too great, upsetting the balance
between combustion air and fuel.
3.34. Most heavy residual oil must be warm
to allow pumping. Preheaters are used to heat
the oil and keep it flowing. For high-visco-
sity oils, the preheater is likely to be loca-
ted at the supply tank. With oils of lower
viscosity, preheaters are often located at the
burner.
3.35. Before the oil reaches the burner, it
is passed through a strainer or filter to re-
move the sludge. This filtering process pro-
longs pump life, reduces burner wear, and in-
creases combustion efficiency.
3.36. The most important consideration in
combustion chamber design is heat release, or
British thermal unit release per cubic foot
of furnace volume. Too high a heat release
will result in excessive furnace temperatures.
Too low a heat release will result in exces-
sive cooling of the flame and smoking fires.
3.37. The size of the combustion chamber
will determine the heat release. The shape
of the chamber will prevent the flame from
impinging on the sides of the furnace where
it would cool, resulting in incomplete com-
bustion and smoke.
3.38. Draft systems can be classified as
natural, induced, or forced or combinations
of these.
A-7
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Combustion of Fuel Oil
3.39. Natural draft results from the dif-
ference in pressure between the stack and the
outside air. Stacks that are too small for
the firing rate will create back pressure.
Too large a stack will cause the same condi-
tions because of internal turbulence and too
cool a stack temperature.
3.40. Induced draft systems require a fan
that sucks combustion products through the
boiler and forces them up the stack.
3.41. Forced-draft systems suck air in
from the boiler room, push it into the boiler,
and force the combustion products up the stack.
3.42. The burning of oil can produce sulfur
oxides, inorganic ash, nitrogen oxides, car-
bon, and unburned hydrocarbons. The sulfur
oxides and inorganic ash are attributable to
the fuel. The air contaminants affected by
burner design and operation are carbon, car-
bon monoxide, aldehydes, organic acids, and
unburned hydrocarbons.
3.43. If a burner is operated properly, no
visible emissions should be caused by oxidi-
zable air contaminants, and the concentrations
of items such as aldehydes and carbon monoxide
should be negligible. Thus, when an oil-
burning system smokes, emits appreciable odor,
or causes eye irritation, there is something
wrong in atomization, mixing, or burning.
The burner and fuel may not be compatible or
the burner may not be properly adjusted.
3.44. Incomplete atomization of the oil
caused by improper fuel temperature, dirty,
worn, or damaged burner tips, or improper
fuel or steam pressure may cause the furnace
to smoke.
3.45. A poor draft or improper fuel-to-
air ratio may also cause smoking.
3.46. Other factors they may cause smoking
are poor mixing and insufficient turbulence
of the air and oil mixture, low furnace tem-
peratures, and insufficient time for fuel to
burn completely in the combustion chamber.
3.47. There are two kinds of hydrocarbon
combustion--hydroxylation and decomposition
(cracking).
3.48. Hydroxylation or blue-flame burning
takes place when the hydrocarbon molecules
combine with oxygen and produce alcohols or
peroxides that split into aldehydes and water.
The aldehydes burn to form C02 and 1^0.
3.49. Decomposition or yellow-flame burn-
ing takes place when the hydrocarbons "crack"
or decompose into lighter compounds. The
lighter compounds then crack into carbon and
hydrogen, which burn to form C02 and H-O. A
mixture of yellow- and blue-flame burning is
ideal.
Boiler Types
3.50. The vast majority of combustion
equipment is used to heat or vaporize water.
These boilers and heaters fall into three
general classifications: fire-tube, water-
tube, and sectional.
3.51. In fire-tube boilers, the heated
gases resulting from combustion pass through
heat-exchanger tubes while water, steam, or
other fluid is contained outside the tubes.
3.52. Fire-tube boilers make up the lar-
gest share of small- and medium-size indus-
trial boilers including the Scotch marine and
fire-box types.
3.53. In all water-tube boilers, the water,
steam, or other fluid is circulated through
tubes while the hot combustion gases pass out-
side the tubes. All large boilers for steam
generation are of this type. The smallest and
largest industrial units are likely to be of a
water-tube design.
3.54. Sectional boilers use irregularly
shaped heat exchanges and cannot be classi-
fied as either water-tube or fire-tube types.
Hot combustion gases are directed through some
of these passages, transferring heat through
metal walls to water or steam in other passa-
ges. These units are manufactured in identi-
cal sections which can be joined together. A
sectional boiler consists of one or more sec-
tions.
Soot Blowing
3.55. Whenever fuels of measurable ash con-
tent are burned, some solids such as carbon
and inorganic ash adhere to heat-transfer sur-
faces in the combustion equipment. These de-
posits must be removed periodically to main-
tain adequate heat-transfer rates. It is
common practice to remove these deposits with
jets of air or steam from a long, retractable
soot blower while the combustion equipment is
in operation. These removed soot particles
are entrained in the combustion gases. Thus,
during these periods of soot blowing the plume
may have an excessive opacity.
3.56. Whenever residual fuel oils or solid
fuels are burned in large steam generators,
tube cleaning is usually conducted at least
once during every 24 hours of operation. At
A-8
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Combustion of Fuel Oil
many power power plant boilers, soot blowers
are operated automatically at 2- to 4-hour
intervals.
3.57. When tubes are blown at 2- to 4-
hour intervals, there is little increase in
the opacity of stack emissions. Intervals
of 8 hours or more between soot blowing can
result in excessive visible opacities.
Black Smoke and White Smoke
3.58. When residual oils or solid fuels
are burned in a deficiency of oxygen, car-
bon particles and unburned hydrocarbons im-
part a visible blackness to the exit gases'.
3.59. Visible emissions ranging from gray
through brown to white can also be created
by the combustion of hydrocarbon fuels, par-
ticularly liquid fuel.
3.60. White or non-black smoke is the re-
sult of finely divided particulates--usually
liquid particlesin the gas stream. These
non-black plumes generally are caused by va-
porization of hydrocarbons in the combustion
chamber. This is sometimes accompanied by
cracking and the subsequent condensation of
droplets. White smoke frequently is attri-
buted to excessive combustion air or loss of
flame.
3.61. Visible plumes of greater than 40
percent opacity are frequently observed at
large oil-fired steam generators, where in-
complete combustion is a relative rarity.
These opaque emissions are commonly attribu-
ted to inorganic particulates and sulfuric
acid aerosols formed by the combination of
sulfur trioxide, moisture, and flue gases.
The condensation of the sulfuric acid aero-
sol may be enhanced by the presence of par-
ticulate matter, which provides condensation
nuclei.
Particulates
3.62. Where combustion is nearly complete,
inorganic ash constitutes the principal par-
ticulate emission. The quantity of these
inorganic solid particulates is entirely de-
pendent upon the fuel. Distillate fuels do
not contain appreciable amounts of ash. In
residual oils, however, inorganic ash-forming
materials are found in quantities up to 0.1
percent by weight. However, even that amount,
when emitted from efficient burning, is not
likely to exceed air pollution control statutes.
3.63. The particulates emitted from normal
oil firing are principally in the submicron
range of diameters where they can cause scat-
tering of light. Over 85 percent of the par-
ticles from efficient oil burning are less
than 1 micron in diameter.
3.64. If incomplete combustion occurs and
carbon or hydrocarbon particles are emitted,
then the average particle size is larger.
3.65. If a light fuel oil is burned in a
deficiency of oxygen, the resulting carbon
particles are likely to be very fine. If a
residual fuel oil is incompletely burned, by
heating it to a temperature of only 200-300°C
and then cooling it the carbon particles are
likely to be in the form of cenospheres.
Cenospheres are hollow, black, coke-like
spherical particles of low density usually
having a minimum dimension of 0.1 micron.
3.66. Particulates emitted from residual
fuel oil combustion consist of 10 to 30 per-
cent ash, 17 to 25 percent sulfate, and 25 to
50 percent cenosphere.
Sulfur Trioxide
3.67. Of the sulfur contained in fuel oil,
95 percent shows up in the exhaust gases as
sulfur dioxide, a colorless gas. Up to 5 per-
cent of the sulfur may be converted to sulfur
trioxide. If the SOj come into contact with
surfaces below the dew point of the gas, the
SOj combines with water vapor to produce sul-
furic acid. This sulfuric acid mist is visi-
ble.
3.68. Concentrations of SOj are negligible
in small equipment, even when fired with high-
sulfur fuel oils. As the equipment sizes and
firebox tempertures increase, SOo concentra-
tions increase rapidly.
3.69. Large steam generators may emit SOo
mist of greater than 40 percent opacity when
fired with oil of greater than 1.0 percent
sulfur.
3.70. Sulfur trioxide tends to acidify par-
ticulate matter discharged from combustion
equipment. This is commonly evidenced by acid
spots on painted and metallic surfaces as well
as on vegetation. Acid damage generally is
the result of soot blowing. (See 3.75.)
3.71. Formation of SOj depends upon several
factors. Concentrations of sulfur dioxide in-
crease with increases in
(a) Combustion chamber tempera-
ture
(b) Oxygen concentration
(c) Vanadium, iron, and nickel
oxide content of the fuel
oil.
A-9
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Combustion of Fuel Oil
3.72. The visible plume from a large oil-
fired unit normally varies from white to
brown, depending upon weather conditions and
the composition of the particulate matter.
3.73. In some cases, the SOj plume will be
detached from the stack. It will become vi-
sible at the point where the sulfuric acid
mist is cooled below its dew point.
3.74. Deposits of dirt which cannot be re-
moved by the normal soot blowing of the heat-
exchanger tubes act as catalysts oxidizing
SC>2 to SOj, with an increased opacity of the
plume resulting. These deposits can be re-
moved by washing, but only at the infrequent
intervals when the steam generator is out of
service.
"Bunkie's Guide to Fuel Oil
Specifications", National Fuel
Oil Institute Technical Bulle-
tin No. 68-101.
Air Pollution Engineering Manual.
edited by J. J. Danielson, DHEW,
PHS Publication No. 999-AP-40,
1967.
Control Equipment
3.75. The only air pollution control de-
vices that have found ready acceptance on
oil-fired power plant boilers are dust collec-
tors used to control particulates during soot
blowing. Dry, small-diameter, multiple cy-
clones are the most common soot-control de-
vices installed.
3.76. Use of centrifugal collectors during
normal operations is worthless since the col-
lectors are not efficient in removing parti-
culates of less than 5-microns diameter, which
is the range in which over 95 percent of the
oil-fired emissions lie.
3.77. The use of electrostatic precipita-
tors for oil-fired power plants is limited to
areas where restrictive legislation requires
low particulate loadings and low opacity of
stack effluents. They collect nearly all the
particulates including the liquid sulfuric
acid droplets. The particulate loading may
be decreased by as much as 90 percent and the
803 emission may be cut in half.
Suggested Additional Reading
Part B
Facts About Fuels.
Oil Burning Equipment.
Other
Emissions From Fuel Combustion. W. S.
Smith, DHEW, PHS Publication No. 999-
AP-2, 1962.
"Stationary Combustion Emissions",
R. B. Engdahl, Air Pollution Vol. 3,
edited by A. C. Stern, 1968.
A-10
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IV. COMBUSTION OF COAL AND ITS CONTROL
Classification of Coal
4.1. The types of coal are
(a) Anthracite (hard coal)
(b) Bituminous (soft coal)
(c) Lignite (brown coal).
4.2. Anthracite coal is mined in Pennsyl-
vania, Rhode Island, and Arkansas.
4.3. There are 23 districts in the United
States which mine bituminous coal.
4.4. Anthracite is less smoky and gives
off less sulfur dioxide, but it is not as
abundant as bituminous.
4.5. After coal is mined, it is generally
prepared before it is used. Raw or unprepared
coal is used in some power plants--mine mouth
plants. Preparation of coal includes crushing
and cleaning to remove impurities, drying to
remove moisture, and separation into the de-
sired sizes.
4.6. Two basic methods are normally used
to describe the composition of coal: the Pro-
ximate Analysis and the Ultimate Analysis.
4.7. Proximate Analysis gives the percen-
tages by weight of the following which are
found in the coal:
(a) Volatile Matter - portion of
the coal that will form gases
and vapors (hydrocarbons, hy-
drogen, and carbon monoxide)
and be driven off when the coal
is heated to 1740 F for 7 min-
utes.
(b) Fixed Carbon - solid portion
that is left when volatile
matter is distilled off. It
is mostly carbon, burns slowly,
and will give a bluish flame.
(c) Ash - portion that will not
burn. Slate, clay, sandstone,
shale, carbonates, pyrite, and
gypsum.
(d) Moisture Content.
The sulfur content in percent and the heat
content in British thermal units per pound
(Btu/lb) are generally also given, although
they are not part of the analysis. This Pro-
ximate Analysis may be made on the coal as
received (AR) or dry (excluding the moisture).
4.8. The Ultimate Analysis gives the che-
mical composition of the coal by dividing the
coal, except for the ash, into its basic ele-
ments.
4.9. In the Ultimate Analysis the volatile
matter and fixed carbon of the Proximate Ana-
lysis are divided into their chemical compo-
nentshydrogen, carbon, oxygen, and nitrogen.
4.10. Another measurement which describes
the coal is the Screen Analysis, or Size Con-
sist. It tells the percentage of the coal that
will fall through a screen with a certain size
opening but which will not fall through the
next smaller size screen.
4.11. The Screen Analysis can be made with a
screen having either round or square holes, but
the two screens will give different totals.
Thus, the type of holes should be specified.
4.12. Coal sizing terms:
Run of mine - unscreened broken coal
from the mine
Slack - all the coal passing through
a screen of a given size,
such as 3/4" slack
Double-screened sizes such as "egg",
"stove", "nut", "pea", and "stoker" -
trade names in bituminous coal that
are standard sizes for anthracite.
4.13. From the air pollution viewpoint, the
amounts of volatile matter, ash, and sulfur,
along with the heating value, are the most im-
portant part of the Proximate Analysis. Vola-
tile matter is related to the emission of smoke;
ash is related to particulate emission. Sulfur
content is related to sulfur oxide emissions.
Heating value is related to the total amount of
pollutant production.
4.14. The size of the coal is important to
the smoke and flue dust emission. The optimum
coal size is determined by the method of firing.
4.15. The impurities in coal are ash, moist-
ure, and sulfur.
4.16. The ash is dispersed throughout the
coal as finely divided matter or is present as
pieces of slate, rock, or clay. The pieces of
ash can be removed in preparation plants by
crushing and washing.
4.17. Power plants usually burn higher ash
coals, while lower ash coals go to the retail
market.
4.18. Moisture may be present as finely di-
vided amounts of water dispersed throughout the
coal or as water clinging to the coal surface.
A certain amount of moisture is helpful in re-
ducing the tendency of coal to form strong coke
in some stokers. It also prevents a dust prob-
lem.
A-11
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Combustion of Coal
4.19. Sulfur is found in coal in three forms:
(a) As an iron disulfide, FeS2,
called pyritic sulfur or as
golden colored iron pyrites
in the form of very heavy balls
or lenses and in small flakes
or crystals or bands as part-
ings. This sometimes is called
"Fools Gold".
(b) Organic sulfur originating with
and forming an inherent part of
the plant life that formed the
coal.
(c) Combined sulfur, generally a
sulfate with calcium or other
mineral matter and seen as a
gypsum with a white surface
or as veins in the coal.
High-sulfurcoal is characterized by the fact
that content of all three forms of sulfur is
high. Very often with high-sulfur coal, the
pyritic form will be as prevalent or more so
than the organic and sulfate forms combined.
4.20. The pyritic sulfur is found in small
discrete particles within the coal; a percen-
tage of this sulfur may be removed by washing
or other mechanical means. However, even after
washing, most of the sulfur in the coal will
be of the pyritic form.
4.21. At present, no economical means is
feasible for the removal of any of the organic
or sulfate forms of sulfur from the coal prior
to its initial use.
Basics of Coal Combustion
and Combustion Equipment
4.22. Some of the terminology describing
characteristics of most coal-burning furnace
systems are as follows:
(a) Fuel bed - layers of coal distri-
buted over a grate which allows
the air to move through the coal
layers.
(b) Stoker for feeding fuel - by which
coal can be added to the bed from
above (overfeed) or below (under-
feed).
(c) Air - which can be introduced be-
neath the coal burning on the fuel
bed (underfire air) or above it
(overfire air).
(d) Arch - the portion of the combus-
tion chamber above the fire; it is
constructed of material capable of
withstanding high temperatures
(refractory material) and is of a
design that will reflect
the heat back into the fire.
(e) Heat-exchange equipment -
converts the heat released
by the coal into a form that
can be used; frequently, the
heat exchange is accomplished
by placing metal tubes at the
exit of the combustion chamber
and converting the water in
these tubes to steam.
(f) Breeching - originally, the
connecting link between the
furnace and the chimney;
currently, one may expect
to find one or more of the
following between the same
two points: (1) economizer,
(2) air preheater, (3) fly-
ash collector (mechanical and/
or electrical), and (4) in-
duced draft fan. In effect,
the breeching thus becomes
a series of short duct-work
connectors.
(g) Chimney - transports the
waste products of combustion
out into the air for disposal
by dispersion.
4.23. Coal will not burn as a solid; no
fuel will. The combustion process must va-
porize, gasify, or break down a solid into
individaul molecules by the addition of heat.
4.24. When coal is burned on grates, one
of two types of feeding mechanisms is gene-
rally usedunderfeed or overfeed.
4.25. The underfeed operation introduces
the primary air and the fuel from below the
grate. The fuel burns from the top to the
bottom of the bed.
4.26. Overfeed operation introduces coal
to the grate from the top and the primary
air from below. Burning occurs from the
bottom to the top of the fuel bed.
4.27. When coal burns in an overfeed bed
on a grate, the process takes place in layers:
(a) At the bottom of the bed and
above the grate where a layer
of ash serves to protect the
grate and preheat the primary
air.
(b) The "oxidation zone", where,
as the air temperature rises,
the heat vaporizes the vola-
tile and carbonaceious ma-
terial from the coal particles
and removes this material. In
A-12
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Combustion of Coal
this vaporous state the com-
bustible material burns in
the reaction:
C + 02 = C02.
This is the hottest part of
the fuel bed.
(c) The "reduction zone", where,
because of the lack of oxygen,
the carbon dioxide combines
with the volatalized carbon-
forming carbon monoxide.
(d) The top layer, where the vo-
latile hydrocarbons and tars
are driven off the fresh coal.
4.28. Unless more air (secondary air) is
introduced, the hydrocarbons and tars crack,
decompose, or condense and are emitted to the
atmosphere as white, yellow, or black smoke.
If oxygen is present in sufficient quantity
at the time the volatile matter is distilled,
the hydrocarbons oxidize completely without
forming soot and smoke through the thermal
cracking and condensation reactions. Secon-
dary air is sometimes called combustion air
and, since it is introduced above the fire,
it is often identical to "overfire air".
4.29. Overfeed fuel beds are smoky because
burning gases rise through fresh fuel, thus
resulting in rapid devolatilization of the
fresh fuel in a zone having a deficiency of
oxygen.
4.30. Underfeed beds are inherently smoke
free. The air and fresh fuel flow upward to-
gether. The zone of ignition, which is near
the point of maximum evolution of the combus-
tible gases, is supplied with ample well mixed
air which promotes complete combustion.
4.31. Heat-exchange equipment converts the
heat released by the burning of the coal into
a form that can be used. There are five cate-
gories :
(a) Radiant heat absorbers - can line
furnace walls with watercooled
surfaces. These surfaces trans-
mit to the water the heat which
is radiated to them.
(b) Boilers or convection heat ex-
changers - the earliest boilers
were tanks containing water
under which a fire was built.
Next, the heated gases from the
furnace were directed around
the water tank and through a
large tube which passed through
the tank. Next, this return
tube was replaced by many small
tubes (3 or 4-in. ID). There
are three types of boilers
in use currently:
(1) Fire-tube boiler -
fire is made in the
large tube and the
gases make several
passes through the
smaller tubes.
(2) "Fire-box" boiler -
gases flow from furnace
through tubes, then re-
verse and flow through
more tubes to the stack.
(3) Water-tube boiler -
water goes from a drum
through several straight
tubes to another drum.
(c) Superheaters or gas-to-vapor
heat exchangers
(d) Economizers or added-convec-
tion heat exchangers
(e) Air preheaters or gas-to-gas
heat exchangers.
Some Terms Used in
Coal Combustion
4.32. Draft is a measure of the positive
pressure or negative pressure (vacuum) or air
or gases in various parts of a combustion sys-
tem. There are several types of draft:
(a) Forced draft - air pressure is
supplied by a fan pushing air
into the system.
(b) Induced draft - a negative
pressure is created by pull-
ing air out of the system
with a fan.
(c) Natural draft - suction in the
system is created when the flue
gases expand and go up the stack.
This causes primary air to be
drawn into the furnace system
to balance out the negative
pressure.
(d) Furnace draft - the pressure
of the gases in the furnace
is positive or negative. If
it is positive, the gases will
leak out of the furnace. If
it is negative, gases will leak
in.
(e) Draft losses - pressure losses
occur as the flue gas flows
through the combustion system.
In principle, both natural and induced drafts
are akin in that they both function from the
A-13
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Combustion of Coal
exhaust or discharge end of the furnace system.
Forced draft functions from the opposite or
feed end of the system.
4.33. Coke is the fixed carbon and ash which
are left after the coal has been heated and the
volatile matter has been driven off. Coking
coal refers to a coal that melts and fuses to
form larger lumps, even though the coal may
have been in small pieces. Bituminous is
usually a good coking coal and anthracite is
not.
4.34. Carbon in the ash - if some of the
coal is heated enough to drive off the volatile
matter but does not finish burning all of the
carbon, the ash will contain some pieces of
unburned carbon or coke.
4.35. Cverfire air - air is injected above
the fuel bed instead of through it as is nor-
mal. The overfire air is forced through jets
or nozzles in the furnace walls. The purpose
of the overfire air jets is to increase the
mixing or turbulence of the gases to insure
complete combustion and prevent smoke.
4.36. Slagging - when molten ash particles
build up on the walls or tubes of a boiler
and flow together, the deposit is called slag
and the process is called slagging.
Plume Visibility
4.37. The visible plume from coal combus-
tion may be caused by condensed water vapor,
sulfur trioxide, sulfuric acid mist, organic
liquids or solids, particulates, and smoke.
(a) Water vapor condenses and pro-
duces a white plume which dis-
sipates rapidly.
(b) Sulfur trioxide and sulfuric
acid mist cause a detached
bluish-white plume that does
not dissipate readily.
(c) Organic liquids and solids
cause a white, yellow, or
brown plume.
(d) Particulates (including fly
ash) cause the plume to be
white, brown, or black.
4.38. Smoke - the black clouds called smoke
are actually small, unburned or partially burned
solid carbon particles and solid or liquid hy-
drocarbon particles. They result from the in-
complete combustion of the volatile products
of the fuel. The carbon of the smoke does not
arise from the free carbon of the fuel but from
the cooling of the hot hydrocarbon gases of the
volatile matter. If these particles are depo-
sited inside the combustion system, they are
called soot.
4.39. Once formed, carbon soot is difficult
to burn. To prevent this soot from being car-
ried away as pollution, the hydrocarbons should
be burned as close as possible to the fuel bed
before they are decomposed by the heat into
soot and smoke.
4.40. It has been found that there is a
marked rise in the percentage of both carbon
(soot) and tar (benzene soluble) contained in
the particulate as the smoke density increases.
4.41. The black smoke plume is visible be-
cause of the size of its solid and liquid par-
ticles. They range between 0.01 and 2.0 mi-
crons in diameter, but most are between 0.3 and
0.6 micron, a size which is highly effective
in scattering or absorbing light.
4.42. These particles between 0.3 and 0.6
micron in diameter contribute little to the
mass of the emissions. Most of the mass is
in the larger particles, which have little
effect in absorbing or scattering light.
4.43. The black shade of a combustion plume
can be reduced by a good adjustment of air-
to-fuel ratio. One indication of this is the
flame in the furnace:
(a) With a good adjustment of air
to the coal feed, the flame
will be yellowish orange in
color with no black tips. It
will appear soft. And its lu-
minosity will give a maximum
of radiant heat-energy transfer.
(b) If the air is increased, the
flame will become whiter in
color and will appear to be
harder, sharper, and more
erosive. Its radiant heat
energy will be lessened.
(c) If the air is decreased too
much, the flame will be
blacker and will appear lazy
and without life. Since a
reducing atmosphere is now
well indicated, soot may be
formed and collect at some
point in the system. The
smoke will be dark.
(d) With a good air adjustment
and proper burning, the smoke
from the chimney should be
just a light haze, either
light tan or light gray in
color.
A-14
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Combustion of Coal
4.44. When a flame impinges on a cold sur-
face, smoke and soot are formed. Complete
combustion should be obtained before the flame
is allowed to hit a cold surface.
Mechanical Coal-Firing Equipment
4.45. Overfeed stokers - earliest type con-
sisted of a steeply inclined grate with alter-
nate stationary and movable sections. Coal
moved down the grate when a lever outside the
furnace was moved.
4.46. Underfeed stokers - two forms: single
retort and multiple retort.
4.47. Single retort - consists of coal hop-
per, one feed trough or retort containing a
feeding device ( a screw or pusher) with the
grate above it. This stoker moves coal (a)
from front to rear in retort, (b) from retort
upward to the grate where it is burned, (c)
sideways on the grate to the ash pits at the
sides. Widely used with smaller boilers.
4.48. Multiple retort - early variety had
one coal hopper across several parallel re-
torts. Ash was dumped periodically from the
rear into an ash pit. Later, all the retorts
were driven by a single crankshaft. They re-
quire forced draft fans. There may be as many
as 18 multiple retorts.
4.49. Traveling grate stoker - grate sur-
face consists of an endless belt with sprock-
ets at either end. Coal hopper with a gate
at one end controls the coal feed. Grate is
moved with gears powered by an electric motor
or turbine. Coal is laid on the grate from
the hopper and is moved through the furnace
as the burning takes place. Ash is dropped
off the grate into an ash pit at the rear.
Presently forced-draft fans are used with
traveling grate stokers.
4.50. Vibrating grate stoker - consists of
a water-cooled grate structure on which the
coal moves from the hopper at the front of
the boiler through the burning zone by means
of a high-speed vibrating mechanism. As with
the traveling grate, the fuel bed progresses
to the rear, where the ash is continuously
discharged. Vibrating stokers may emit
slightly higher concentrations of fly ash
than traveling-grate stokers because of in-
creased agitation of the fuel bed.
4.51. Spreader stoker - consists of a coal
hopper, a feeding mechanism, and a device that
injects the coal into the furnace (usually a
rotating flipper). The coal is thrown into
the furnace and partly burned in suspension.
The larger particles fall to the grate and
burn there. Essentially, the spreader stoker
employs overfeed burning, an inherently smoky
method, plus suspension burning, an inherently
smoke-free method producing fly ash. Over-
fire jets have been found essential to smoke-
free operation. They also reduce dust emis-
sion significantly, but not enough to meet
most ordinances, unless a particulate collec-
tor is used.
4.52. Pulverized-fuel firing unit - in
this system, coal is pulverized to particles,
at least 70 percent of which pass through a
200-mesh sieve (median size of the particles
is 5.0 microns. In direct-firing systems,
raw coal is dried and pulverized simulta-
neously in a mill and is fed to the burners
as required by the furnace load. A prede-
termined coal-air ratio is maintained for any
load. In indirect-firing systems there are
storage bins and feeders between the pulveri-
zers and burners. Pulverized-fuel firing
units are of two basic types--wet bottom and
dry bottom. In a wet-bottom unit, the tem-
perature in the furnace is maintained high
enough so that the slag does not solidify
(or fuse) and it can be removed from the
bottom as a liquid. The dry-bottom furnace
maintains a temperature below this point so
that the ash will not fuse. The steam elec-
tric plants, where pulverized fuel firing is
used most, emit 50-80 percent of the ash
fired in the coal as fine fly ash. Therefore,
all modern plants of this type must have high-
efficiency dust collectors.
4.53. Cyclone furnace - fires crushed coal
that is nearly as fine as pulverized coal in-
to a water-cooled, refractory lines cylindri-
cal chamber 8 to 10 feet in diameter. The
coal and air swirl in a cyclonic manner as
the burning proceeds. Combustion is so in-
tense that a small portion of the molten ash
coating the wall of the chamber is vaporized.
Approximately 85 percent of the ash fired is
retained as molten slag; hence, the fly-ash
load is much lower than with pulverized coal.
However, the ash which does escape the cy-
clone is extremely fine and thus difficult to
collect.
4.54. Pulverized-coal burners and cyclone
furnaces are the universal equipment for
firing coal in the large new electric-gene-
rating stations.
4.55. Some types of burning equipment
(underfeed stokers, overfeed stokers, spreader
stokers, and pulverized-fuel burners) make use
of a certain amount of fly-ash reinjection.
In this process, cinders are returned to the
grate from the fly-ash collector and burned
again to reduce the loss of unburned carbon.
The usefulness of this method is limited, for
A-15
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Combustion of Coal
whenever the fly ash is reinjected pneumati-
cally, the total fly ash from the unit is
eventually increased.
Causes and Control of Particulate
Emissions From Coal Combustion
4.56 Emissions of smoke and particu-
lates may be caused by the type of coal, the
type of combustion equipment, or improper com-
bustion.
4.57. Improper combustion - if a furnace pro-
duces smoke, either the fuel and air are not in
balance or the three T's of combustion are not
being satisfied. The cause may be one or more
of the following conditions:
(a) Insufficient, air for the amount
of fuel
(b) Improper distribution of the
air or fuel
(c) Too much air (usually overfire
air), which chills the flame
before all combustion is com-
plete
(d) Insufficient turbulence or
mixing of the air
(e) Cold fire box - often caused by
excessive furnace draft, which
pulls outside air into the fire
box through doors and leaks; it
usually occurs at low load.
4.58. Possible causes for improper distri-
bution of air or fuel
(a) Uneven depth of fuel bed
(b) Plugged air holes in the grate
(c) Clinkei which shuts off air
flow
(d) Leaky seals around the edges
of the grate area
(e) Improper burner adjustment
Possible reasons for insufficient tur-
(a) Insufficient overfire air
(b) Plugged overfire air nozzles
(c) Nozzles that are improperly
aimed
(d) Incorrect burner adjustment
(e) Excessive furnace draft
4.59.
bulence
4.60. Importance of coal and equipment in
particulate emissions
(a) Type of firing - least emission
occurs with underfeed stokers,
the greatest with pulveri-
zed coal
(b) Furnace design - least emis-
sion with large furnaces and
greatest with small furnaces
of pulverized coal furnaces
(c) Secondary air jets tend to
reduce emission
(d) Coal size - the greater the
proportion of small sizes,
the greater the emissions.
Smaller sizes are more easily
swept up the chimney.
(e) Volatile content - high-vola-
tile coal results in a long,
opaque flame that is more
likely to strike the cooler
surfaces of the furnace re-
sulting in soot formation.
Low-volatile fuel burns with
a short, transparent flame.
(f) Amount of ash - the higher
the ash content, the greater
the emission of fly ash
(g) Fly-ash reinjection - if fly ash
is reinjected, there can be an
accumulation in the furnace of
suspended solids formed from
the combustible portion of the
coal.
(h) Firing rate - as the firing
rate increases, the velocity
of the gases passing through
the furnace increases. And
as the velocity increases,
more and larger particles are
carried out of the furnace.
4.61. The most important variable in hand-
fired furnaces is the volatile content of the
fuel burned, the smoke potential increasing
rapidly as volatile content increases.
4.62. Several types of control equipment
have been used to collect the particulates
from coal combustion:
(a) Settling chambers
(b) Large-diameter cyclones
(c) Multiple small-diameter
cyclones
(d) Wet scrubbers
(e) Electrostatic precipitators.
4.63. The settling chamber is a low-effi-
ciency, low-cost, low-pressure-drop device.
It generally is applied to natural-draft, sto-
ker-fired units. Collection efficiency is 50
to 60 percent.
A-16
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Combustion of Coal
4.64. Large-diameter cyclones have higher
pressure drops. Their efficiency ranges from
65 percent for stoker-fired units to 20 per-
cent for cyclone furnaces.
4.65. Multiple small-diameter cyclone units
are used as precleaners for electrostatic pre-
cipitators or as final cleaners. Efficiencies
range from 90 percent for stoker-fired units
to 70 percent for cyclone furnaces.
4.66. Wet scrubbers are limited to the con-
trol of particulate emissions during soot
blowing, although alkaline scrubbers to re-
move both fly ash and sulfur dioxide are
under development.
4.67. Electrostatic precipitators are the
most commonly used devices for cleaning the
gases from large, stationary combustion sour-
ces such as those burning pulverized coal.
They are capable of efficiencies up to 99 per-
cent.
4.68. Efficiency of collection for cyclone
collectors increases as the load increases.
An increase in the carbon content of coal is
usually associated with an increase in size
distribution. Thus, as firing rate increases
or the carbon content of the coal increases,
the centrifugal collector becomes more effi-
cient.
4.69. The electrostatic precipitator be-
comes less efficient as the load increases. An
increase in carbon content is associated with
an increase in electrical resistivity. Electro-
static precipitators are not generally used for
high-carbon ash, which is derived from stokers.
They are best adapted to pulverized coal-fired
units.
Suggested Additional Reading
Part B
Facts About Fuels.
Coal Burning Equipment.
Design of Coal Combustion Equipment.
Other
Atmospheric Emissions From Coal Com-
bustion. W. S. Smith and C. W. Gruber,
DHEW, PHS Publication No. 999-AP-24,
1966.
"Stationary Combustion Emissions",
R. B. Engdahl, Air Pollution Vol.
3, edited by A. C. Stern, 1968.
Emissions From Coal-Fired Power Plants.
S. T. Cuffe and R. W. Gerstle, DHEW, PHS
Publication No. 999-AP-35, 1967.
A-17
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V. OTHER COMBUSTION EMISSIONS: INCINERATORS.
AGRICULTURAL BURNING. NATURAL GAS AND
MOBILE SOURCES
The combustion of coal and fuel oil in
stationary sources produces a large number of
visible plumes. More efficient combustion of
these fuels can reduce the opacity of the
plumes produced from these sources. Other
types of combustion, both for the production
of usable energy and for the burning of waste
materials, will produce black and non-black
plumes. Some of these combustion sources and
the cause and control of their plumes are dis-
cussed in this section.
Solid Waste Disposal
by Incineration
5.1. The methods of burning solid waste in-
clude the use of open-top or trench incinera-
tors, conical metal ("tepee") burners, domestic
incinerators, apartment-house incinerators, and
municipal incinerators as well as open burning.
5.2. Incinerators can be classified in sev-
eral ways, such as by their size, their method
of feeding, the type of waste they will handle,
or the number of combustion chambers they con-
tain.
5.3. A single-chamber incinerator is de-
signed so that feeding, combustion, and ex-
haust to a stack take place in one chamber.
5.4. The multiple-chamber incinerator has
three or more separate chambers in series for
admission and combustion of the solid refuse,
mixing and further combustion of the fly ash
and gaseous emissions, and settling and col-
lecting of the fly ash.
5.5. Multiple-chamber incinerators are of
two general types:
(a) Retort, in which the ignition
chamber, mixing chamber, and
combustion chamber are arranged
in a "U"
(b) In-line, in which the three
chambers follow each other in
a line.
5.6. The tepee burner has been used by the
lumber industry to incinerate wood wastes and
by some small cities to dispose of municipal
refuse. These burners range from 10 to 100
feet in height. They are single-chamber in-
cinerators and are not designed to minimize
atmospheric emissions; thus, they rarely meet
visible emission regulations when in use and
have considerable fly-ash fallout.
5.7. The tepee burner may be fed by a bull-
dozer, a dump truck, or a conveyor. Feeding
with bulldozers or trucks requires that the
doors at the base of the burner be opened.
This stops the motion of the draft air in-
side the burner and cools the combustion
gases. The dumping of the charge on the
burning pile smothers the fire. All of these
factors contribute to incomplete combustion
and additional smoke.
5.8. Domestic incinerators may range from
units such as a single-chamber backyard wire
basket to dual-chamber incinerators having a
primary burner section followed by an after-
burner section. Many air pollution control
agencies have banned backyard incinerators
and some have banned all types of domestic
incinerators.
5.9. The emissions of smoke and fly ash
from apartment-house incinerators are often
high because of low combustion temperatures
and improper air regulation.
5.10. Apartment-house incinerators may be
of two types--flue-fed and chute-fed. In the
single-chamber flue-fed unit, refuse is
charged down the same passage that the pro-
ducts of combustion use to leave the unit.
Refuse dropped onto the fuel bed during burn-
ing smothers the fire, causing incomplete
combustion and emission of smoke.
5.11. A chute-fed multiple-chamber incin-
erator has separate passages for refuse
charging and combustion-product emission.
Nevertheless, the emissions from this incin-
erator often exceed emission standards. One
cause is the high natural draft in the flues
of the tall stacks that go to the top of the
apartment house. This high draft carries with
it a large amount of particulates.
5.12. Incinerators used for commercial or
industrial establishments may be single or
multiple-chamber types and may handle from
50 to several thousand pounds of refuse per
hour.
5.13. The average capacity of municipal
incinerators is 300 tons of refuse per day.
They may be fed in batches or continuously.
Continuous-feed units are preferable, because
operating parameterssuch as combustion-
chamber temperatures that affect particulate
emissions--can be closely controlled.
5.14. The gases leaving an incinerator may
have temperatures as high as 1800 F, which is
much higher than the 600 F maximum for steam-
generating boilers. The higher temperatures
mean a higher plume rise but also a greater
A-18
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Other Combustion Emissions
volume of gas and more expensive breechings,
chimney linings, and air pollution control
equipment.
5.15. Some rules that should be met by any
incinerator to minimize the particulate emis-
sions are as follows:
(a) Air and fuel must be in proper
proportion and mixed adequately.
(b) Temperature must be sufficient
for combustion of both solid
fuel and gaseous products.
(c) Furnace volume must be large
enough to provide adequate time
for complete burning of the com-
bustible materials.
NOTE - these rules are a restatement of the
"three T's of combustion".
5.16. Some operating practices that can help
to reduce the smoke from incinerators include
the following:
(a) On a cold start, feed nonsmoky
material slowly and increase the
frequency of the chargenot its
sizeuntil the secondary com-
bustion chambers get hot.
(b) If smoke is a problem, keep the
charging opening practically
blocked with waste.
(c) It is often an advantage to mix
slow-burning material with flash-
burning material. This can be
done to achieve more efficient
incineration of wet garbage or
it can be done to reduce smoke
by mixing smoky materials, such
as plastics and rubber, with
paper waste.
(d) Excessive fly ash is usually the
result of too great a draft. The
draft can frequently be reduced
by partially closing the damper,
which is installed in the breeching
between the furnace and the stack.
5.17. Dark smoke from incinerators consists
primarily of small carbon particles resulting
from incomplete combustion. The dark smoke
may mask the light-colored plumes also emitted
from the incinerator.
5.18. Light-colored plumes are emitted from
most municipal incinerators. These plumes are
caused by volatilization of particles or by
chemical reactions in the fuel bed. Analysis
of the plume shows appreciable quantities of
metallic salts and oxides in microcrystalline
form which were transformed into the vapor
state in the fuel bed and then condensed.
Removal of these very small particles from
the flue gases is difficult. The equivalent
opacity of the plume can be partially reduced
by proper incinerator design.
5.19. Large fly-ash particles may be either
charred material or incombustible particles.
If complete combustion is achieved, there
should be no charred particles. The incom-
bustible material may come from chemical reac-
tions in the fuel bed. It may also be from
small particles that were present in the re-
fuse.
5.20. The size of the particles formed by
chemical reactions may range from submicron
to 10-mlcron diameters. Much of the weight
of the particulate matter is in the particles
greater than 5 microns. These can be removed
from the combustion emissions by collecting
devices.
5.21. Several types of collection devices
which have been used with incinerators and
their efficiencies (by total weight of all
particles without regard to size) are given
in the following tabulation:
Collection Device
Settling chamber
Welted baffle-spray system
Cyclones and multiple cyclones
Wet scrubbers
Electrostatic precipitators
Bag filters
Collection
Efficiency,
percent
10-35
10-53
60-80
94-96
96-99+
99+
The use of bag filters for incinerators is
very limited. Their utilization depends on
considerations of temperatures and moisture
content of the gas stream as well as the
pressure drop across the filter.
5.22. The per capita quantity of solid
waste generated in the United States has
been increasing in recent years. The physi-
cal and chemical properties of the garbage
have also been changing. Moisture content
has been decreasing with diminishing house-
hold garbage. As a consequence of the de-
creasing use of coal for home heating, there
are less ashes for disposal. The combustible
content and the heat value of the solid waste
have been increasing, principally because of
the greater use of paper and plastics.
5.23. In a study of incineration in tepee
burners, several observations were made re-
garding the density of smoke produced when
different types of material were burned:
(a) Plastic products (polyvinyl
chloride, etc.), rubber pro-
ducts, and asphalt products
A-19
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Other Combustion Emissions
(tar paper, linoleum tar blocks,
etc.) produced Ringelmann No. 5
or 100 percent equivalent opacity
smoke.
(b) Leather products produced copious
quantitites of Ringelmann No. 5
cmoke lasting for hundreds of
yards downwind.
(c) Ashes from home used produced
Ringelmann No. 3 to 4 smoke.
(d) If the refuse contained garbage
of more than 15 to 20 percent
by weight and if this garbage
was not mixed uniformly with
dry refuse, smoke emissions of
No. 4 to 5 Ringelmann generally
occurred.
(e) If the charge contained more than
30 percent damp material even
when mixed with dry combustible
material, the pile tended to
smolder, producing an undesirably
large amount of smoke. Further-
more, the buildup of a large pile
of charged refuse cut down on the
draft through the pile and con-
tributed to additional incomplete
combustion.
The study recommended that plastic, rubber,
asphalt, and leather products not be burned
in tepee burners.
Agricultural Burning
5.24. Open burning of several kinds is done
in connection with agriculture. The burning is
done for waste disposal, for disease pest con-
trol, and as part of harvesting or land manage-
ment. All of these types of burning will re-
sult in visible smoke and other air pollution
effects such as visibility reduction, fallout
of carbonaceious residues, contributions to
photochemical smog, and odors.
5.25. For some of this burning, there is a
flexibility in the time when the burning can
be done in the area that can be burned during
any one fire. In these cases, the burning
should be scheduled for periods when meteoro-
logical conditions such as wind speed and in-
version height are conducive to good disper-
sion of the smoke. However, the winds cannot
be too strong or there may be a chance of the
fire getting out of hand.
5.26. Burning of this type includes the
cleaning out of weeds and brush when chemical
methods are undesirable, the removal of the
slash remaining after logging operations, the
clearing of potato vines, peanut vines, and
sugarcane leaves prior to harvest.
5.27. Other agricultural burning cannot be
scheduled. One example is the burning of
smudge pots in orchards to reduce the hazard
from frost. Another is disposal of cattle
affected by hoof and mouth disease at a time
of the year when burial is not possible be-
cause of frozen ground or other reasons.
5.28. Other agricultural burning includes
the burning of field crops such as barley and
rice, the removal of prunings from fruit and
nut trees, the incineration of brush, and the
burning of cotton gin waste to aid in the con-
trol of bollworms.
5.29. The density of the smoke from agri-
cultural burning will depend upon the com-
bustion temperature and the residence time of
the fuel at that temperature. If the moisture
content of the fuel is high, the smoke will
be of a white shade indicating the presence
of water vapor. The greener the plant life,
the more moisture it contains and the whiter
the smoke will be.
Combustion of Natural Gas
5.30. The particulate emissions from the
normal combustion of natural gas are insig-
nificant compared with those from coal and
oil. Control equipment is not utilized to
control the emission from natural gas com-
bustion equipment.
5.31. Natural gas constituents normally
includes methane (CH^), ethane (C2 Hg) in
varying proportions, and lesser amounts of
nitrogen (N2) and carbon dioxide (C02).
5.32. The table compares the chemical com-
position of typical samples of coal, fuel oil,
and natural gas:
Content, percent
Hydrogen
Carbon
Sulfur
N2, 02, etc.
Ash
Coal
5
78
3
7
7
100
Oil
10
86
3
0.6
0.4
100
Gas
24
75
trace
1
-
loo
5.33. One should note the high percentage
of hydrogen in natural gas. This high per-
centage results in a large amount of water
vapor being present in the gases exhausted
from combustion. As a consequence, the plume
from natural gas combustion under certain
ambient temperature and moisture conditions
can be a very dense white plume of condensed
water vapor.
A-20
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Other Combustion Emissions
5.34. The water produced in combustion will
absorb 900 Btu's in changing from the liquid to
the vapor state. Thus, fuels containing more
hydrogen provide less available heat than fuels
containing small amounts of hydrogen.
5.35. In heat-generating installations, one
of the principal components is the heat ex-
changer. The heat exchanger contains the me-
dium, such as water, that is to be heated, and
its outside surface area is exposed to the hot
gases generated by the burning fuel. Boilers
are rated on the total area of heating surface
of their heat exchangers.
5.36. Burners can be divided into two broad
classifications - atmospheric and mechanical
draft.
5.37. The atmospheric burner depends en-
tirely upon the negative pressure within the
furnace to draw combustion air through the
burner assembly. Natural draft can be created
by a stack. Theoretically, the draft is pro-
portional to the difference between the stack
temperature and ambient temperature and to the
height of the stack.
5.38. The mechanical draft burner depends
upon a blower (usually, a forced-draft blower
not an induced-draft blower) to supply the com-
bustion air to the burner. With this type of
burner a low-profile building with a short
"stub" stack can be used to house the boiler.
5.39. Smoke from the stack of a natural gas
installation is evidence of improper operation
of the gas burner, specifically, that there is
insufficient combustion air.
5.40.
will be
Other indications of insufficient air
(a) A burner flame that is extremely
rich, having an orange-red appear-
ance
(b) Soot deposits on heat-exchanger
surfaces
(c) Burner pulsation
(d) Excessive gas consumption.
5.41. One of the common reasons for insufi-
cient combustion air--one that is frequently
overlookedis the lack of adequate fresh air
opening into the boiler room. There must be
some permanent provision (not just an open
window) to ensure that fresh air will always
be supplied to the combustion equipment. One
of the first indications of an inadequate air
supply is a hot, stuffy feeling in the boiler
Engines Used in Transportation
5.42. There are three commonly-used en-
gines used in the United States to propel
surface vehicles and aircraft. These are
the spark-ignited internal combustion engine,
the compression-ignited internal combustion
engine, which is frequently referred to as
the diesel, and the aircraft gas-turbine en-
gine.
5.43. The first of these is used in auto-
mobiles, light-duty trucks, light aircraft,
motorcycles, outboard motors, and small gaso-
line utility engines.
5.44. The diesel engine is used in large
trucks, buses, locomotives, ships, and heavy
construction equipment.
5.45. The gas-turbine engine is commonly
used on large aircraft.
5.46. Both types of internal combustion
engines can be subdivided into four-stroke-
cycle and two-stroke-cycle engines. These
two operating cycles differ in the number of
times the piston rises in the cylinder during
the combustion of the fuel in the cylinder.
Both cycles consist of four parts. The opera-
tions that take place in the spark-ignition
engine during the four parts of the cycles
are:
(a) Intake of air and fuel
(b) Compression of fuel-air mix-
ture during which ignition of
the mixture is set off by the
spark from a spark plug
(c) Expansion of the burning mix-
ture, forcing down the piston
and delivering the power which
drives the vehicle
(d) Exhaust of the burned gases
out of the cylinder.
5.47. The differences between the gasoline
and diesel engines are the method of ignition
and the fuel systems. In the diesel engine
the fuel does not enter the cylinder as a
mixture with the air but is injected into the
cylinder through nozzles during the phase
when the air is being compressed to a high
pressure and high temperature. Fuel injected
into this high-temperature air ignites with-
out a spark.
5.48. The aircraft gas turbine consists of
four main sections: a compressor, a combus-
tion chamber or combustor, a turbine, and a
tailpipe.
A-21
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Other Combustion Emissions
5.49. When a plane is moving, air is forced
into the front of the engine where the com-
pressor is. The compressor, a multibladed fan,
compresses the air to several times its density,
increasing its temperature and pressure.
5.50. The compressed air then passes into
the combustors, into which fuel is sprayed.
The mixture of fuel and air is ignited pro-
ducing a high-temperature exhaust gas.
5.51. This exhaust gas is expanded into the
turbine. The expansion drives the turbine,
giving it sufficient power to rotate the com-
pressor blades.
5.52. After passing through the turbine,
the exhaust gas may still have enough velo-
city to provide a backward push against the
outside air helping to thrust the aircraft
forward.
5.53. There are three categories of air-
craft gas-turbine engines: turbojet, turbo-
prop, and turbofan.
5.54. The turbojet engine uses a great pro-
portion of the energy of the turbine exhaust
gases to provide thrust for the aircraft.
This is done by designing a suitable exit
nozzle. Turbojet engines perform best at
high altitudes and high speeds.
5.55. Turboprop engines have a propeller
mounted in front of the compressor. They are
designed so that most of the energy of the
expanding exhaust gases is used in turning the
turbine and subsequently to rotate the pro-
peller. These engines operate best at low
altitudes.
5.56. In the turbofan engine the fans of
the first stages are larger in diameter than
the others. The air taken into the center
portion of the compressor passes through as
with the turbojet engine. The exhaust gases
turn the turbine, driving the compressor, and
expand out the rear of the engine producing
additional jet thrust. Because of the in-
creased frontal area of this engine, it is
better adapted to subsonic than to supersonic
flight.
Visible Emissions From
Mobile Sources
5.57. Particulate matter is emitted from a
gasoline engine in the exhaust gases and in
the blowby gases, which escape past the piston
rings into the crankcase and then into the ex-
haust.
5.58. Carbon, metallic ash, and hydrocar-
bons in aerosol form are the principal parti-
culate emissions. If an automobile is per-
forming properly these particles will essen-
tially all be less than 5 microns in size and
not visible as smoke.
5.59. The color of smoky exhausts may be
blue, black, or white. Blue and black smoke
are indicators that the engine needs repair.
5.60. White smoke results from the conden-
sation of water vapor in the exhaust. There
is always water vapor produced in the combus-
tion of gasoline. White smoke from an exhaust
will be more likely during cold weather when
the vapor is cooled to the visible liquid
state. The white smoke will be more notice-
able on moist days when the air is saturated
so that the wet plume cannot evaporate and
when an automobile is standing still so the
plume is not dispersed by, the motion of air.
5.61. If the exhaust smoke has a bluish
tinge, oil is leaking into the combustion
chamber of the engine and is being burned
there with the gasoline.
5.62. Oil can enter the combustion chamber
in three ways: through a cracked vacuum pump
diaphragm, through an excessive clearance
around the intake valve, and between the pis-
ton rings and the cylinder walls. The latter
entry may be due to worn cylinder walls or to
worn or carboned rings.
5.63. Black exhaust smoke is composed of
unburned gasoline. This indicates that the
fuel-to-air mixture is excessively rich in
fuel.
5.64. Some causes of black smoke from a
gasoline engine are
(a) Excessive fuel pump pressure
or pump leakage
(b) Choke not opening properly
(c) Clogged air cleaner
(d) Carburetor in need of re-
pair or adjustment
(e) Faulty spark plugs which
cause the engine to "miss"
and not use all the fuel.
5.65. The California Motor Vehicle Code
states that "No vehicle shall be operated in
a manner resulting in the escape of excessive
smoke, flame, gas, oil or fuel residue". "Ex-
cessive" is not defined, but it can be inter-
preted to mean any quantity of smoke which
draws attention to the vehicle which is emit-
ting it.
A-22
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Other Combustion Emissions
5.66. Particulate matter emitted by diesel
engines consists primarily of carbon and hy-
drocarbon aerosols, which result from incom-
plete combustion of the fuel. Diesel exhaust
is made up of particles of which 62.5 percent
are less than 5 microns in diameter and 37.5
percent are from 5 to 20 microns.
5.67. Maximum emissions of visible smoke
from diesel engines occur during full-throttle
acceleration and during deceleration or "lug-
down", also at full throttle. At full or open
throttle the fuel-to-air ratio is enriched.
This fuel-rich mixture is desirable during
acceleration because it provides greater power.
The greater power is achieved at the expense
of fuel economy.
5.68. The power of the diesel engine is
controlled by the amount of fuel injected in-
to the combustion chamber through nozzles
during the compression phase of the engine
cycle.
5.69. If the fuel system is kept at the
setting prescribed by the manufacturer, the
smoke emissions should meet established stan-
dards. As vehicle mileage increases, low
levels of visible emission can be maintained
by proper fuel system adjustment, maintenance
at appropriate intervals, use of specified
type of fuel, and good operating techniques.
Maintenance will correct dirty or eroded in-
jection nozzles, which can occur even in a
properly adjusted engine.
5.70. It has been found that truck opeators
sometimes increase the horsepower of their en-
gines by altering the fuel-injection setting
prescribed by the manufacturer. By this means
the operator can install an engine which is
underrated for the load required and then meet
the power requirement by overfueling. However,
this increase in power also raises the level of
black smoke.
5.71. Most turbine engines in nonmilitary
aircraft use aviation kerosene as a fuel. The
turbine engines operate at fuel-to-air ratios
five to twenty time less than those used by
piston engines. During flight the emissions
of particulates are low. However, during the
takeoff and landing operations, the engines
operate under high fuel-to-air ratio condi-
tions and visible smoke is emitted. The
quantity of the solid material released is
small, but is highly visible.
5.72. Particulate matter originates near
the upstream end of the combustor, where fuel
is injected and where the fuel-rich regions are.
Alteration programs for replacing smoking en-
gines involve the replacement of conventional
combustors (for burner cans) with new smokeless
burner cans.
5.73. A series of tests on different kinds
of conventional aircraft turbine engines has
been run to determine the density of the
smoke emitted under different power settings
including idle, takeoff, climb-out and ap-
proach power. The results are given in the
following table. For the JT3C-6 engine, the
dense smoke emissions at takeoff power were
largely caused by the water augmentation in
this engine. The water injection is used for
additional thrust on takeoff from a standing
start to an altitude of approximately 500 feet.
Power Setting
Engine Number
and Type Idle Takeoff Climb-out Approach
501-D13
Turboprop
JT3D-3B
Turbofan
JT8D-1
Turbofan
CJ805-3B
Turbojet
JT3C-6
Turbojet with
water augmen-
tation
-------
Other Combustion Emissions
Control and Disposal of Cotton
Ginning Wastes. DHEW, PHS Publi-
cation No. 999-AP-31, 1967.
Air Pollution Aspects of Tepee
Burners. T. E. Kreichelt, DHEW,
PHS Publication No. 999-AP-28,
1966.
A-24
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VI. NONCOMBUSTION EMISSIONS AND WATER VAPOR PLUMES
6.1. Discussed below are some of the equip-
ment and the industries that may emit visible
plumes. Where available, the size distribu-
tion of the particles will be listed. Some of
the equipment types are basic to several in-
dustries and processes so these types of equip-
ment will be discussed first and then referred
to in the industry discussions.
Furnaces
6.2. There are several types of furnaces
for melting metals. They are reverberatory,
cupola, electric, crucible, and pot. Most
of these furnaces discharge high-temperature
effluents containing dusts and fumes which
are less than 1 micron in size. These ef-
fluents must frequently be cooled before
they are ducted to a control device. The
control device must be capable of high-ef-
ficiency collection of submicron particles.
6.3. The reverberatory furnace usually
consists of a shallow, generally rectangular
refractory hearth for holding the metal to be
melted. The furnace is enclosed by vertical
walls and covered with a low refractory-lined
roof. Combustion of the fuel occurs directly
above the metal in the furnace. The heat is
radiated from the burner flame, roof, and
walls onto the metal. (The radiation "rever-
berates" within the furnace.)
6.4. The largest reverberatory furnace is
the open hearth furnace used in steel manu-
facture. The charge of metal is introduced
through doors in the front wall; finished
steel and slag are poured out of a tap hole
in the rear wall. Heat is provided by pass-
ing a luminous flame with excess air over
the charged metal.
6.5. Other reverberatory furnaces are
cylindrical and may be fired by a flame which
enters the end of the cylinder or is directed
tangentially along the side of the cylinder.
These furnaces are frequently used in non-
ferrous (that is, excluding iron and steel)
industries for smelting small amounts of alu-
minum, brass, and alloys of several metals.
6.6. The cupola furnace is normally used
in gray iron foundries, where iron is melted
and poured into a mold or casting. This fur-
nace is also used to melt copper, brass,
bronze, and lead.
6.7. A cupola is a refractory-lined cylin-
der open at the top and equipped with air in-
lets (called tuyeres) at the bottom. Alter-
nate layers of metal, coke and limestone are
dumped from a charging door in the side of
the cupola onto a burning coke bed in the
bottom of the furnace. The combustion air
for burning the coke is forced upward through
the tuyeres and layers of charge by a blower.
The heat generated by burning of the coke
melts the metal, which is drawn off through
a tap hole. The charging and melting is a
continuous operation. Large amounts of fine
particles are carried off in the gases.
6.8 There are four types of electric fur-
naces: direct arc, indirect arc, resistance,
and induction.
-,<
6.9. In the direct-arc furnace, graphite
and carbon electrodes are placed below the
slag cover of the metal. The current passes
from one electrode through the slag, through
the metal charge, and back through the slag
to the other electrode. The heat is generated
by radiation from the electric arc between the
electrodes and from the resistance to the pas-
sage of electricity in the metal.
6.10. In the indirect-arc furnace the me-
tal charge is placed below the electrodes and
the arc is formed between the electrodes and
above the charge. Indirect-arc furnaces are
used mainly in the steel industry.
6.11. The induction furnace consists of a
crucible within a watercooled copper coil.
An alternating electric current in the coil
around the crucible induces eddy currents in
the metal charge. The movement of these
eddies develops heat within the mass of the
charge. This furnace is used for the produc-
tion of both ferrous and nonferrous metal and
alloys.
6.12. In the resistance furnace, the elec-
trodes may be buried within the metal charge
or placed above it. The charge itself acts
as the electrical resistance and generates
the heat. The resistance furnace is used to
melt metals such as ferroalloys at tempera-
tures up to 6000 F.
6.13. A crucible furnace consists of a
large, covered metal pot lined with refractory
materials such as clay-graphite mixtures or
silicon carbide. There is a small hole in the
lid for charging the metal and exhausting the
products of combustion. The crucible of re-
fractory material rests on a pedestal in the
center of the furnace and flames from gas or
oil burners are directed tangentially around
it. This furnace is used for melting metals
with melting points below 2500 F.
6.14. Pot furnaces may by cylindrical or
rectangular and consist of an outer shell
lined with refractory material, a combustion
chamber, and a pot. The pot is made of iron
or steel and in it are placed metals which
A-25
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Noncombustion Emissions and Water Vapor Plumes
will melt below 1400 F. The pot rests in the
furnace which supports it above the floor of
the combustion chamber. When melted, the me-
tals in the pot are removed by tilting the pot
or by pumping or dipping.
Driers
6.15. A drier is a device for removing wa-
ter or other volatile material from a solid
substance. Air contaminants emitted include
dusts and vapors.
6.16 A rotary drier consists of a rotating
cylinder inclined to the horizontal with ma-
terial fed from the higher end discharged at
the lower end. In the direct rotary drier,
heated air or combustion gases flow through
the cylinder in direct contact with the ma-
terial. Air flow may be in either the same
or the opposite direction as the flow of ma-
terial. Dust carryout increases proportion-
ately to the square of the increase in air
flow through the drier.
In another type, the indirect rotary drier.
heat is applied by combustion gases on the
outside of the cylinder or through steam
tubes inside the cylinder.
6.17. The direct rotary drier has "flights"
attached to the inside of the cylinder. As
the cylinder rotates, the flights pick up the
material and shower it down through the gas
stream. Thus, the direct rotary drier has
very high potential for dust emissions. It
cannot be used for drying fine material be-
cause loss of product would be excessive. In-
direct rotary driers are usually used for
drying powdery material since they have less
tendency to emit dust.
6.18. The flash drier consists of a furnace
or source of hot gases, a device for dispersing
the wet material through the gases, a duct through
which the gases convey the material, and a collection
system for removing the dried material from
the gas stream.
6.19. xhe spray drier consists of a drying
chamber, a source of hot gases, a device for
atomizing the solution particles to be dried,
and a means for separating the dry product
from the exhaust gases. Atomization is achieved
by either disks which rotate at a high speed,
high-pressure nozzles, or nozzles which use
air or steam to break up the particles. The
dried product is generally separated from the
exhaust gases and collected in a cyclone sep-
arator.
6.20. A tray or compartment drier consists
of a chamber containing racks on which are
placed trays of wet material to be dried.
Heated air circulates over the wet material
until the material reaches the desired mois-
ture content.
Terminology in Metallurgical
Processing
6.21. The metallurgical industry can be
divided into primary and secondary metals in-
dustries. The primary metals industries pro-
duce the metal from ore. The secondary me-
tals industry includes the production of al-
loys and the recovery of the metal from scrap
and salvage.
6.22. The initial objective of metallurgical
operations is to convert the metal ore scrap
to a purer form of the metal and then to mix
it with other elements to form an alloy. Some
of the processes used in these purifying opera-
tions are smelting, refining, electrolytic
duction, sweating, and sintering. Sometimes,
two of these terms describe the same process.
6.23., The process of heating ores to a
high temperature in the presence of a reducing
agent such as carbon (coke) and of a fluxing
agent (such as limestone) to remove the accom-
panying clay and sand is termed smelting.
6.24. In the smelting of iron ore the ore
is heated in a blast furnace with coke and
limestone at a temperature above the melting
point of iron and slag (a mixture of the im-
purities and the limestone flux). The molten
iron (the more dense material) and molten
slag (the less dense material) are removed
separately from the furnace. The limestone
flux helps to purge the metal of impurities
and renders the slag more liquid.
6.25. Electrolytic Reduction - In this
process a molten compound containing the me-
tal is placed in an electrolytic cell known as
a pot which consists of a steel tank lined
with refractory insulating bricks. The com-
pound is decomposed by a continuous direct
electric current which flows between the cath-
ode and the anode. The purified metal will
flow to one of these electrodes and be depos-
ited there.
6.26. Roasting - This process involves
heating the material to a temperature not
high enough to melt the material but high
enough to cause it to oxidize or become
pulverized. The process can also be called
calcining.
6.27. Sweating Furnace Sweating can be
accomplished in a furnace when the raw ma-
terial is composed of two metals having
different melting temperatures. The sweating
A-26
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Noncombustion Emissions and Water Vapor Plumes
furnace temperature is carefully controlled so
that the metal with the lower melting point be-
comes liquid and flows from the furnace. After
this metal is removed, the furnace burners are
extinguished and the metal with the higher melt-
ing point is raked from the hearth.
6.28. Sintering - A mixture of ore-bearing
fine particles and fuel such as coal or coke
is burned. The object is to partially melt
or sinter the material into relatively coarse
particles that are more suitable for other met-
allurgical operations than were the fine par-
ticles.
6.29. Quenching - The immersion of hot met-
als or coke in liquid baths in order to effect
rapid cooling is termed quenching. The purpose
of quenching ordinary steel is to harden it.
6.30. Materials which will resist change of
shape, weight, or physical properties at high
temperatures are known as refractories. The ma-
terials that are chiefly used for refractories
are fire-clay, silica, kaolin, diaspore, alumina,
and silicon carbide. Refractories are used most
often in the form of bricks.
Iron and Steel Mills
6.31. To make steel, iron is reduced to pig
iron in a blast furnace (smelting) and most of
its impurities are removed as slag. The pig
iron is transformed into steel in open hearth
(reverberatory) furnaces, basic oxygen furnaces,
or electric furnaces, where carbon, manganese,
silicon, and other impurities are oxidized to
form gases and slag. The concentrations of
the impurities are reduced to the limits spe-
cified for steel.
6.32 The blast furnace is the chief means
for reducing iron ore to pig iron. The reduc-
tion process is carried out at a high tempera-
ture and in the presence of a fluxing substance.
Furnaces may be 90-100 feet high and of varying
diameters. At the top of the furnace is a
double bell, which forms an air lock for the
admission of materials during continuous opera-
tion of the furnace.
When in use, the blast furnace is first
charged with alternate layers of coke, ore,
and limestone. The coke is ignited at the
bottom and is rapidly burned under the in-
fluence of a forced draft of air blown from
the base upward through the furnace. As the
coke is burned away, the material moves down-
ward in the furnace while the stack is kept
full by fresh charges admitted through the
bells. The iron at the bottom is tapped off
at intervals through an "iron notch". The
lighter slag may also be tapped off through
a "cinder notch".
As the hot gases from the combustion region
pass upward from the furnace they heat the
fresh charges. They then pass out of the
furnace through ducts which carry them to
purifying equipment. This gas contains about
25 percent carbon monoxide with the remainder
being chiefly inert gases. After the gas is
passed through dust collectors and scrubbers,
it can be burned in stoves which preheat the
air going into the blast furnace.
6.33. "Slips" are the principal operating
factor which causes partlculate pollution
from blast furnaces. A slip results from
arching of the charge of coke, limestone, or
iron ore across the inside of the furnace.
When the arch finally breaks and the burden
slips downward, there is a rush of gas to the
top of the furnace, which develops abnormally
high pressures that cannot be handled by the
gas-cleaning equipment. When this occurs,
safety valves open to relieve the pressure
and to discharge a dense black or red cloud
of dust to the air. Slips reduce efficiency
and the steel industry is constantly striving
to reduce their incidence. Even under normal
conditions most of the particles emitted from
blast furnaces are larger than 50 microns.
6.34, The basic oxygen converter is a
cylindrical container open at one end for
charging and pouring and for oxygen injec-
tions. In this steel-making process, oxygen
is blown at high velocity through a water-
cooled pipe downward onto the surface of the
mixture of molten pig iron, scrap iron, and
scrap steel. This results in violent agita-
tion and mixing of the oxygen with the iron.
Rapid oxidation of the dissolved carbon and
silicon follows forming slag and gases.
6,35, Sintering plants convert iron ore
fines and blast furnace flue dust into a
coarser material more suitable for charging
to a blast furnace. This is done by applying
heat to a mixture of the ironcontaining ma-
terials and coke on a slow-moving grate
through which combustion air is drawn.
6.36. Major sources of dust in sintering
plants are the combustion gases drawn through
the bed and the exhaust from the grinding,
screening, and cooling of the sinter. Most
of the particles discharged in the sintering
process are large and fall out of the air as
dustfall.
6.37. Most of the coke used in blast fur-
naces is produced in "by-product" coke ovens
from bituminous coal. The by-product gases
from the coke ovens are processed in a by-
product plant, where such items as tar, am-
monia, and light oils are removed. The re-
maining coke-oven gas is used as fuel in a
variety of furnaces throughout the steel plant.
A-27
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Noncombustion Emissions and Water Vapor Plumes
6.38. The coke plant consists of a battery
of long, narrow firebrick ovens separated by
combustion chambers. Coal is introduced into
the red hot ovens through holes in the top of
the battery. When the coking is finished (17-
18 hours), doors at the ends of the oven are
opened and a pusher ram shoves the entire
charge of coke into a railway car. The hot
coke will burn in the air until the car is
conveyed to a quench tower where huge quanti-
ties of water are used to extinguish the burn-
ing. Dust, steam and gas emissions occur
during charging, discharging, and quenching
operations. Since the ovens in a battery are
sequentially operated, the pollutants are dis-
charged at a fairly constant rate. Most of
the smoke and dust emitted at the coke oven
site result from the inadequacies of the charg-
ing process, but there is also leakage of
smoke and gases because of poorly fitted or
sealed oven doors.
6.39, Air contaminants are emitted from an
open hearth furnace throughout the process,
which may last 10 hours. Oxygen injection
(lancing) into the furnace speeds the process
but increases the amount of air pollution
emitted. The pollutants emitted are fumes,
dust, and gases, with up to 90 percent being
the red iron-oxide fumes. Other contaminants
may arise from the grease and oil contained
in the steel scrap. About 50 percent of the
emissions are particles less than 5 microns
in diameter.
Open hearth shops often contain several
furnaces, each having an exhaust stack.
Because of the cost of pollution control and
the growing obsolescence of open hearth fur-
naces, they are being replaced by basic oxy-
gen furnaces and electric furnaces.
6.40. More emissions are created by basic
oxygen furnaces (EOF) than by open hearth
furnaces; however, all BOF's in the United
States are equipped with electrostatic pre-
cipitators or venturi scrubbers. The open
mouth of the EOF converter is covered by a
hood, and the emissions are conducted to the
collectors. The particle size of the emissions
is small; 85 percent are less than 1 micron in
diameter.
6.41. In the steel industry, electric arc
furnaces are smaller than other types and are
used primarily to produce special alloy steels.
Heat is furnished by direct-arc electrodes ex-
tending through the roof of the furnace. Dust,
fumes, and gases are emitted, but only 40 to
50 percent of the dust is iron oxide, an amount
considerably less than that emitted by the
other furnaces. Approximately 70 percent by
weight of the particles are smaller than 5 mi-
crons. Over 95 percent effective collection
can be achieved with appropriate hooding and
high-efficiency collection equipment.
Gray Iron Foundries
6.42. Gray iron foundries melt and cast
iron. The cupola, electric, and reverbera-
tory furnaces are used; however, the cupola
is the one most often employed. Plant sizes
range from small job cupolas operated several
hours a day to large units operated contin-
uously for several days.
Particulate emissions are composed of iron
oxide, dust smoke, oil, grease, and metal
fumes. Between 20 and 25 percent of the dust
and fume particles are less than 5 microns in
diameter. The dust in the discharge gases
arises from dirt on the metal and from fires
in the coke and limestone charge. Smoke and
oil vapor come primarily from partial combus-
tion and from distillation of oil on the
greasy scrap charged to the furnace.
The exhaust gases which carry the particu-
lates are hot and voluminous, this requiring
a control system designed to handle large
flows. The most effective control system in-
corporates an afterburner to eliminate combus-
tibles and a fabric filter to collect the dust
and fume. Coolers must be installed to cool
the effluent before it reaches the baghouse.
6.43. Other possible sources of particu-
lates at foundries are the core ovens which
bake the cores used in the sand molds. The
cores contain binders that require baking to
develop the strength needed to resist any
erosion and deformation when the molten iron
is poured into the mold. Sometimes, when
special binders are used in the core, the
ovens will emit fine aerosols that can have
excessive opacities and cause eye irritation.
Normally, an afterburner can control these
pollutants.
Nonferrous Metallurgical Industry
6.44. The primary and secondary recovery
of copper, lead, zinc, and aluminum are the
chief nonferrous metallurgical industries.
6.45. Part of the production of aluminum
involves the electrolytic reduction of alumina
(an oxide of aluminum) in a pot which also
contains cryolite and fluoride salts. The
effluent released during the pot reduction
process contains hydrogen fluoride, fluoride
fumes, and fine particles of alumina and
carbon. The emission from some pot furnaces
also contain hydrocarbon tars.
A-28
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Noneombustion Emissions and Water Vapor Plumes
6.46. Secondary aluminum operations involve
making lightweight metal alloys for industrial
castings. Crucible furnaces, reverberatory fur-
naces, or sweating furnaces may be used. Flux-
es help remove the dissolved gases and oxide
particles from the molten bath. Chlorine gas
is lanced into the molten bath to reduce the
magnesium content. It forms aluminum chloride
fumes having a small particle size. If the
scrap charged is oily or greasy, smoke is given
off. The fluxes used also produce particulate
matter.
6.47. The primary smelting of lead and zinc
involves converting the sulfide of both ores
to oxide through roasting and sintering opera-
tions. A mixture of sinter, iron, coke, and
limestone flux is charged into blast furnaces
where the burning of the coke reduces the lead
oxide to molten lead before being tapped off.
The effluent gases from the roasting, sintering,
and smelting operation contain considerable
lead dust.
6.48. Zinc oxide from the roasting of the
ore or from processing the slag from the lead
smelter can be converted into metallic zinc
by the electrolytic reduction or by distilla-
tion in retorts or furnaces. The distillation
invloves the heating of a mixture of zinc
oxide and coke until a zinc vapor is formed
and the oxygen in the zinc oxide combines
with the carbon in the coke to from carbon
monoxide. The zinc vapor passes into a con-
denser where it is converted into a liquid.
During this refining process, zinc fumes and
dust are discharged. In spite of hoods, bag-
houses, and electrostatic precipitators, the
white zinc oxide fume arising from the plant
is a distinctive characteristic of a zinc re-
tort plant.
6.49. Scrap and salvage are the raw materi-
als of the secondary metals industry. A sub-
stantial quantity of lead is recovered from
automobile batteries. Various types of furnaces
are used. The discharge of air contaminants
from melting furnaces is generally caused by
the excessive temperatures and by the melting
of metal contaminated with organic material.
If fuming fluxes such as ammonium chloride are
used in zinc smelting, a fume of ammonium chlo-
ride will be observed above the molten metal.
6.50. Over 95 percent of the particulate
emission from the secondary smelting of zinc
and lead are less than 5 microns in diameter.
Much of this is composed of oxides of lead
and zinc, but there are also sulfides and sul-
fates. Under high temperatures, zinc vapor
will form the white zinc oxide fume. Both
lead and zinc oxide fumes produce very opaque
effluents.
6.51. The recovery of copper from copper
sulfide ore involves roasting in multiple
hearth furnaces, smelting in reverberatory
furnaces, and "converting" by passing thin
streams of air through a mixture of iron and
copper sulfide. These processes emit CO,
sulfur oxides, nitrogen oxides, and a fine
particulate plume. The partlculates consist
of oxides, dust, and sulfuric acid mist.
6.52. The plumes from the primary smelting
of copper, lead, and zinc contain concentra-
tions of sulfur oxides which are quite large
compared with the other large source-coal and
oil-fired power plants.
6.53. Copper is called brass when alloyed
with zinc and is termed bronze when alloyed
with tin. The remelting of nearly pure cop-
per and bronze produces only small amounts
of metal fumes due to high boiling tempera-
tures and low pouring temperatures of copper
and tin. However, the secondary smelting of
brass can produce zinc oxide fumes consisting
of submicron particles.
Petroleum Refineries
6.54. Major sources of particulate matter
at refineries are catalyst regenerators,
sludge burners, and the air-blown asphalt.
Minor emissions come from heaters, boilers,
and emergency flares.
6.55. Modern refining processes include
many operations using solid-type catalysts.
These catalysts become contaminated with coke
buildup during operation and must be regener-
ated by burning off the coke under controlled
combustion conditions. The flue gases from
the regenerator vessel may contain hot cata-
lyst dust, oil mists, aerosols, carbon mono-
xide, and other combustion products. If no
control devices are used, a visible plume
will be emitted. Its degree of opacity will
depend upon the atmospheric humidity.
6.56. The catalytic cracking processes
are used: fluid catalytic cracking (FCC) and
thermofor catalytic cracking (TCC). The cata-
lyst regenerator will be different for each
catalytic cracking reactor:
(a) The regenerator for the FCC units
may be located alongside, above,
or below the reactor. These re-
generators normally have a ver-
tical cylindrical shape with a
domed top. External size varies
from 20 feet in diameter by 40
feet high to 50 feet in diameter
by 85 feet high. Internal cy-
clones and external electrostatic
A-29
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Noncombustion Emissions and Water Vapor Plumes
precipitators and carbon monox-
ide boilers are used to con-
trol the emissions.
(b) TCC regenerators, referred to
as kilns, are usually vertical
structures with horizontal,
rectangular, or square cross
sections. Typically, one may
be 10 feet square by 45 feet
high. Wet centrifugal col-
lectors are used as dust col-
lectors.
6.57. Asphalt is the residue from petroleum
drilling after all the other fractions have
been boiled off. The residual asphalt can be
refined by air blowing the residue at elevated
temperatures. Oxygen in the air combines with
hydrogen in the oil molecules to form water
vapor. Hydrogen is removed until the asphalt
reaches the desired consistency. The blowing
is carried out in horizontal or vertical cy-
lindrical-shell stills equipped to blanket
the charge with steam. Air blowing of asphalt
generates oil and tar mists and malodorous
gaseous pollutants.
6.58. At petroleum refineries, the incinera-
tion or open burning of the heavy petroleum
residues and inorganic materials such as clay,
sand, and acids can be a major source of par-
ticulate emissions. This sludge is atomized
in much the same way as heavy fuel oil. While
the organic material can be burned, the inor-
ganic matter is entrained in the exhaust gases
and emitted as fine dust.
6.59. To prevent unsafe operating pressures
in process units during shutdowns and startups
and to handle miscellaneous hydrocarbon leaks
or temporary high-pressure conditions, a re-
finery must provide a means for venting hydro-
carbons safely. One method is to incinerate
them in an elevated-type flare. Such flares
introduce the possibility of smoke composed
of carbon particles resulting from incomplete
combustion. Smokeless combustion is often pro-
moted at elevated flares by introducing steam
through nozzles at the top of the stack. The
steam jets provide turbulence and mixing with
the ambient air.
Portland Cement and Lime Plants
6.60. Raw materials for the manufacture of
Portland (gray) cement are ground, mixed, and
blended by either a wet or a dry process. In
the wet process the crushed raw materials are
mixed with water and ground and mixed wet. In
the dry process the ingredients are used dry.
Raw materials consist of two basic ingredients-
lime-bearing material and clayey-material.
After the raw materials are crushed and
ground, they are introduced into a rotary
kiln and heated. The kiln is a rotating
steel cylinder lined with refractory brick
which ranges from 6 feet in diameter by 60
feet in length to 25 feet in diameter by
760 feet in length. Heating continues until
the mixture reaches 2200 F, at which tempera-
ture a chemical reaction takes place raising
the temperature to 2700-2900 F. Cement clink-
ers about the size of marbles are produced
which are cooled and ground to a powder.
During the grinding, gypsum is added to pre-
vent the cement from hardening too fast when
mixed with water.
6.61. The largest amount of particulate
emission at cement plants accompanies the
exhaust gases leaving the kilns. Over 85
percent of the particles carried out by
these gases are smaller than 20 microns in
diameter. Dust is also generated from the
rotary driers used in preparation of material
for the dry process and from the loading of
cement into bags, trucks, and railroad cars.
6.62. Fabric filters and electrostatic
precipitators preceded by mechanical col-
lectors are generally the controls used.
6.63. Gaseous emissions from the combus-
tion of fuel in the kilns are usually minor.
Most of the sulfur dioxide from the sulfur
in the fuel combines with the lime and alka-
lies such as calcium oxide.
6.64. Lime is produced by calcining various
types of limestone in continuous rotary or
vertical kilns lined with refractory material.
This is accomplished by heating the limestone
in the kiln to 2000 F, driving off the carbon
dioxide and leaving calcium oxide, which is
called quicklime. Two of its most important
single uses are for refractory materials and
steel fluxing.
The dust generated by rotary lime kilns
ranges from 5 to 15 percent by weight of the
lime produced. Vertical kilns emit 1 percent
by weight. About 28 percent of the particles
are greater than 44 microns in diameter which
is the size range collected in dustfall jars.
About one-third are less than 20 microns in
diameter.
Kraft Pulp Mills
6,65. The basis of all paper products is
cellulose. The main source of cellulose is
wood, although rags can also be used. The
fibers of cellulose are bound together with
lignin in the pulpwood. There are several
chemical pulping processes for separating
A-30
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Noncombustton Emissions and Water Vapor Plumes
the cellulose from the lignin: sulfite; sulfate
or kraft; soda; and alpha. Over three-fourths
of the production is done by the kraft and sul-
fite processes. Both emit characteristic odors;
however, the kraft process emits a greater
quantity and there are eight times as many
kraft as sulfite mills. The malodorous gases
include hydrogen sulfide, methyl mercaptan,
dimethyl sulfide, and sulfur dioxide.
6.66. In the kraft process, wood chips are
mixed with a cooking liquor of sodium sulfide,
sodium hydroxide, and water and cooked under
steam pressure for about 3 hours in a large,
upright vessel called a digester. During the
cooking period the pressure is reduced period-
ically to prevent overburdening of the digester;
this is accompanied by steam emissions.
When the cooking is completed, the bottom of
the digester is suddenly opened and its contents
are forced into a blow tank. The cellulose then
proceeds through several processes to the fin-
ished product. The spent black liquor contain-
ing the lignin is drained from the blow tank
for processing to recover the chemicals for re-
use. It is concentrated in multiple steam
evaporators, further concentrated in a direct
contact evaporator, burned in a recovery fur-
nace, and dissolved in a smelt tank.
The green liquor is pumped into a causticizer,
where the sodium carbonate is converted to so-
dium hydroxide by the addition of calcium hy-
droxide for reuse in the dlgestor. The calcium
carbonate, also produced in the causticizer, is
converted into calcium carbonate in a lime kiln
and the calcium hydroxide is reused in the
causticizer.
6.67. The major source of particulate emis-
sions in kraft pulping is the exhaust from the
recovery furnace. Sodium sulfate, which is non-
odorous, is the major particulate. Sodium car-
bonate and carbon particles are also emitted.
As the exhaust gases from the recovery furnace
pass to the chimney, some of their heat is used
to evaporate the black liquor in the direct-
contact evaporator. The water vapor produced
by the evaporation can produce a sizable white
plume when it condenses in the atmosphere.
6.68. Other particulate emissions are lime
dust from the lime kiln; mists from the smelt
tank, causticizer, digester, and blow tank, and
combustion products and unburned bark from the
bark-burning boiler.
Sulfuric Acid Manufacturing
6.69. Basically, the production of Sulfuric
acid involves the generation of sulfur dioxide
(S02), its oxidation to sulfur trioxide (S03>,
and the hydration of SO, to form sulfuric acid.
The sulfur dioxide can be generated by burn-
ing sulfur or sulfur-bearing materials such
as hydrogen sulfides from oil refineries.
The highly concentrated sulfur oxide emissions
from primary smelters are also used as input
to the acid-making process although the con-
taminants such as dust must be removed from
the S02 gas if high-quality is to be produced.
6.70. The two main processes of producing
sulfuric acid are the chamber process and the
contact process. Over 90 percent of the sul-
furic acid in the United States is produced
by the contact process.
6.71. In the chamber process the S02 is
oxidized to SOj by the reduction of nitrogen
dioxide (N02) to nitrogen oxide (NO), and
then it is combined with water vapor. This
is accomplished as the hot S02 flows through
a Glover's Tower, several lead chambers, and
two Gay Lussac towers. The function of the
Gay Lussac towers is to recover the nitrogen
oxides (NO and N02>. The final Gay Lussac
tower is the primary source of emissions in
the chamber process. These emissions include
nitrogen oxides, sulfur dioxide, and sulfuric
acid mist. About 50 percent of the total ni-
trogen oxides is N02 which characterizes the
exit gas by a reddish-brown color.
6.72. The contact process uses a catalyst,
vanadium pentoxide, to oxidize the S02 to
S0j in a catalytic converter. The 803 gas is
cooled in an economizer and then passes to an
absorbing tower where most of it is absorbed
in a circulating stream of 99 percent sulfur-
ic acid. The SOj combines with the water in
the acid to form more sulfuric acid. Any
unabsorbed SOj passes through to a stack to
the atmosphere. The tail-gas discharge from
the absorbing tower constitutes the only sig-
nificant air-contaminant discharge from a con-
tact sulfuric acid plant. Most of these tail
gases consist of nitrogen, oxygen, and carbon
dioxide, but the S03 which is emitted will
hydrate and form a sulfuric acid mist upon
contact with the atmosphere. Under improper
operating conditions, startups or emergency
shutdowns, the opacity of this mist can be
very dense. Minor mist emissions may come
from the converter, towers for drying S02,
tank-car vents, or leaks in the process
equipment.
6.73. The predominant factor in the visi-
bility of an acid plant's plume is the par-
ticle size of the acid mist rather than the
weight of the mist discharged. Acid particles
larger than 10 microns deposit readily on
duct and stack walls and contribute little to
the opacity of the plume. Acid mist composed
of particles less than 10 microns in diameter
is visible in the absorber tail gases. As
A-31
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Noncombustion Emissions and Water Vapor Plumes
the particle size decreases, the plume becomes
more dense because of the greater light-scat-
tering effect of the smaller particles.
Nitric Acid Plants
6.74. The ammonia oxidation process is the
principal method of producing commercial ni-
tric acid. It involves three main steps
(a) A mixture of ammonia (NHj) and
air is passed through a catalyst
at high temperatures. Nitric
oxide (NO) and water are formed.
(b) When no NO stream is cooled, the
NO reacts with the oxygen remain-
ing in the mixture to form nitro-
gen dioxide (N02).
(c) The M>2 is cooled further and is
passed to an absorber where it is
absorbed in water to produce a
50 to 60 percent nitric acid
(HN03).
If a higher strength nitric acid is required,
the weak acid is processed in an acid concen-
trator where some of the water is removed by
mixing the nitric acid with concentrated sul-
fur ic acid in a dehydrating column. Some
gases are produced in this process and they
are passed through an absorber tower to re-
cover weak nitric acid.
6.75. The principal source of emissions in
a nitric acid plant is the absorber. The tail
gases from the absorber contain nitric oxide,
nitrogen dioxide, nitrogen, oxygen, and trace
amounts of acid mist. Small amounts of N02
are also lost from acid concentrators and acid
storage tanks. Nitric oxide is a colorless
gas; nitrogen dioxide is red-orange-brown in
color.
6.76. Abatement of the effluents from absorp-
tion towers can be effected by mixing the gases
with natural gas and passing them over a cata-
lyst bed. The nitrogen dioxide and nitric
oxide are dissociated and converted into nitro-
gen, carbon dioxide, and water vapor. These
gases are then released from a stack.
Paint and Varnish Manufacturing
6.77. Protective coating manufacturing may
include the processing of pigments, natural
or synthetic resins, drying oils, solvents,
driers, and plasticizers. The pigments give
the paint color and covering power. The re-
sinssuch as rosin--contribute to the drying
speed, hardness, and gloss. The pigments are
dissolved in drying oils such as linseed oil,
which by oxidation and polymerization (the
combination of several simple molecules into
a complex molecule) forms a hard film when
applied to a surface. Solvents or thinners,
such as turpentine, reduce the viscosity of
the paint so that it can be spread easily.
Upon application, they evaporate from the
surface. The driers, such as cobalt soap,
are catalysts which accelerate the hardening
of the oil film. Plasticizers may be added
to keep the hardened film elastic so that it
will not crack when subjected to vibration.
6.78. Much of the manufacturing process
consists of cooking these ingredients at ele-
vated temperatures to cause decomposition of
the products. As long as the cooking is con-
tinued, these decomposition products are
emitted to the atmosphere. A cook may average
8 to 12 hours. The quantity, composition, and
rate of emission depend upon the ingredients
in the mix, maximum temperature, rate of
heating, stirring, method of introducing
additives, and the extent of air or inert
gas blowing.
6.79. Emissions include organics, odors,
vapors, fumes, gases, and particulate matter
ranging from 2 to 20 microns in dimension.
Scrubbers have little effect on most of these
small particles.
Hot-Mix Asphalt Batching Plants
6.80. All hot-mix asphalt plants incorpo-
rate the following processes: conveying pro-
portioned quantities of cold aggregate (stone,
gravel, and sand) to a dryer, heating and
drying the aggregate in a rotary drier, screen-
ing and classifying the hot aggregate in bins,
weighing out the desired quantities of aggre-
gate sizes, heating the asphalt oil, mixing
the hot aggregate and hot asphalt in the
proper proportions, and delivering the hot
mixture into trucks which haul it to the
paving site. Strictly speaking, this mixture
of aggregates and asphalt cement should be
called asphalt concrete or bituminous concrete,
but it is frequently referred to as just
"asphalt".
6.81. Dust originating in the aggregate is
the major atmospheric pollutant from asphalt
plants, and the principal source of this dust
is the rotary drier. The dust is carried out
through the upper end of the drier with the
exhaust gases. Other important sources of
dust are the vibratory screens, unenclosed
bucket elevators, weigh hopper, storage piles
and bins, and traffic dust from the yard.
6.c32. Most driers employ a single dry cy-
clone as a precleaner which collects 70 to 90
percent of the exhaust dust. This precleaner
A-32
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Noncombustion Emissions and Water Vapor Plumes
catch is discharged back into the bucket ele-
vator where it rejoins the heated aggregate
and continues in the process. Of the parti-
culate emissions from the precleaner, 25 per-
cent have size between 5 and 10 microns and
35 percent are less than 5 microns in dia-
meter.
6.83. Frequently, the elevators, hot bins,
and screens are hooded or covered and the
fugitive dust from them is fed into the exhaust
from the dry cyclone. This combination of dust
then can be cleaned from the exhaust gases by
centrifugal or baffled scrubbers. By this
combination of collectors, high removal effi-
ciencies are possible; however, a visible
water vapor plume will be emitted as part of
the exhaust from the wet scrubber.
Phosphoric Acid Manufacture
6.84. Two processes are used to manufacture
phosphoric acid. High-purity acid for use in
the food, detergent, and plastic industries
is produced by the thermal process, also called
the phosphorus-burning process. The wet pro-
cess is used to manufacture less pure phospho-
ric acid for the phosphate fertilizer industry.
6.85. Phosphate rock contains a compound
consisting of calcium, phosphorus, oxygen,
and fluorine. This compound can be reduced
(driving off the oxygen) in an electric fur-
nace so that pure phosphorus is produced.
Pure phosphorus ignites immediately when ex-
posed to air; therefore, it is generally
submerged under water. For use as-a raw
material in the thermal-process phosphoric
acid manufacture, the phosphorus is usually
converted to a liquid, placed under water,
and shipped in a tank car.
6.86. Thermal-process phosphoric acid manu-
facture involves three steps:
(a) Oxidizing (burning) the liquid
phosphorus by mixing it with air
in a combustion chamber to pro-
duce the compound phosphorus
pentoxide (P-O,.) vapor.
(b) Passing the vapor into a hydrator
where it is mixed with water or
weak phosphoric acid to produce
a higher strength phosphoric acid
mist.
(c) Removing the mist from the gas
stream in an absorber. The strong
phosphoric acid is then stored
for shipment or is treated fur-
ther if it is to be used in the
food industry.
6.87. The principal atmospheric emission
from the thermal process is the acid mist
which is emitted from the absorber and fails
to be collected by the electrostatic precipi-
tator or mesh-entrainment separators. The
mist particles are generally less than 5 mi-
crons in diameter.
6.88. This mist is extremely hygroscopic
so that, unless there is a high collection
efficiency, a dense white plume of 100 per-
cent opacity is emitted from the stack. The
plume may range from 40 to 50 percent water
vapor. Depending on weather conditions and
acid mist concentration, the plume usually
dissipates in a few hundred feet.
6.89. In the wet process of phosphoric
acid manufacture, finely ground phosphate
rock is decomposed by sulfuric acid in a reac-
tor (or digester) tank for a period of several
hours. During this process weak phosphoric
acid and gypsum crystals are created.
6.90. The slurry of these two compounds is
sent to a filter system (e.g., a tilting pan
vacuum filter), where the gypsum cake is
washed out leaving 32 percent acid.
6.91. This acid is then concentrated to 54
percent in an evaporator or concentrator.
6.92. Phosphate rock may contain as much as
4 percent fluorine. Emissions from wet-process
phosphoric acid manufacture consist of rock
dust, fluoride gases (primarily silicon tetra-
fluoride), fluoride particulates, and phospho-
ric acid mist.
6.93. Most of the particulate emissions
come from the reactor and some from the filter.
These particulates are often removed by wet
collectors.
6.94. The reactor, the evaporator, and the
filter are all sources of fluoride emissions.
6.95» Most of the phosphate rock mined in
the United States is mined in Florida. This
is where most of the wet-process phosphoric
acid plants are and where much of the phosphate
fertilizer manufacture is carried on.
Phosphate Fertilizer Manufacture
6.96. Three different manufacturing pro-
cesses produce three phosphate fertilizers,
each having a different grade of phosphorus
pentoxide (P20g) nutrient. These are normal
superphosphate (18 percent), a triple super-
phosphate (45 percent of 54 percent), and
diammonium phosphate (64 percent).
A-33
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Noncombustion Emissions and Water Vapor Plumes
6.97. In each of these processes there are
emissions of participates, silicon tetrafluoride
and hydrogen fluoride. The particulate dusts
are visible; the fluorides can cause damage
to livestock through fluorosis.
6.98. Many of the particulate emissions come
during the drying of the fertilizer and during
the handling of it on conveyor belts or in cu-
ring and storing sheds.
6.99. Dust is also produced in plants that
granulate the fertilizer or blend it. In gran-
ulation, the particle size of the fertilizer
is increased to aid in the handling and storage
of the fertilizer.
6.100. Normal superphosphate fertilizer is
being replaced by high-analysis fertilizers.
It is produced by mixing dry-ground phosphate
rock with sulfuric acid. The mixture is poured
into a large enclosed container or "den", where
it solidifies. The solid is then shaved off
by cutters and stored for drying. The major
portion of the emissions comes from the sto-
rage building.
6.101. Triple superphosphate is produced
by a continuous process in which dried and
ground phosphate rock is mixed with phospho-
ric acid. The product can be treated in
several ways:
(a) It can be discharged to a slow-
moving belt where it becomes
solidified. Then it will be
stored in a curing building.
After 30-60 days it is dug out
from the "pile" in the curing
shed and then crushed, screened,
and shipped.
(b) It can be fed as a slurry to a
"blunger" where it is mixed by
rotating blades and granulation
is begun. Then the granulation
is completed in heated dryer
kilns.
(c) The cured and screened triple
superphosphate produced in (a)
can also be passed through a
drum granulator in the presence
of steam and then dried in a
horizontal rotary kiln.
6.102. The usual methods of control in the
phosphate fertilizer industry are scrubbers,
inertial separators, and fabric filters.
Soap and Synthetic Detergent Manufacture
6.103, The production of soap normally in-
volves the hydrolysis or "splitting" of fats
to obtain fatty acids, followed by boiling
the fatty acids with sodium or potassium hy-
droxide in large kettles for several days.
6.104. After cooking, the soap is dried to
remove the moisture and can be finished in
several different forms--bars, flakes, chips,
or powder. The hot-air process is used to
dry the soap for bars, flakes, and chips.
Soap powder is finished by spray dryingthe
blowing of hot air upward in tall towers while
soap drops are falling downward.
6.105. Synthetic detergents are produced
by combining a fatty alcohol or linear alky-
late with sulfuric acid and then neutralizing
it with caustic. The product is a paste
mixed with water. The paste is pumped to a
large (possible 100 feet high by 20 feet in
diameter) spray tower where it is dried to
the desired moisture content.
6.106. The principal sources of particulate
matter in the making of soap and synthetic
detergents are the spray drying of products
and the handling of dry raw materials. Fabric
filters are widely used to control dusts from
handling.
6.107. The hot exhaust from the tower con-
tains fine particles together with moisture
evaporated from the soap or detergent during
the spray drying. Often, the exhaust is
passed through both a cyclone and a wet
scrubber before it is released.
6.108. The exhaust is close to the satura-
tion temperature, particularly if a wet scrub-
ber is used, and it will form a dense white
plume which is principally condensed water
vapor.
Wet Plumes
6,109, Most air contains some amount of
water in the vapor or gaseous phase. Water
in this vapor phase is invisible. Only when
it is changed to the liquid or solid phase
does the water become visible as clouds, fog,
rain, snow, etc.
6.110. Relative humidity is one measure of
the amount of water vapor in the air. The
warmer the air is, the more water vapor it
can hold without the vapor condensing into
the liquid state. Thus, the relative humidity
of air can be increased-in two ways:
(a) Adding more moisture
(b) Cooling the air.
6.111. If either of these methods for in-
creasing relative humidity is carried on long
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Noncombustion Emissions and Water Vapor Plumes
enough, the air becomes saturated. Any more
water vapor added or any further cooling results
in the excess water vapor changing phase and
becoming visible.
6.112. If hot, moist effluent is released
to a cooler atmosphere, the moisture will con-
dense to form an opaque white plume; if the
relative humidity of the atmosphere is high,
this plume will persist for some distance down-
wind from its emission point.
6.113. The visible water plumes may be ob-
jectionable if they
(a) Contribute to the formation of
ground fogs which obscure visi-
bility for automobiles or air-
planes
(b) Contribute to icing conditions
when they come in contact with
very cold surfaces
(c) Combine with some other gas (such
as sulfur trioxide) to form a
harmful pollutant (such as sulfuric
acid)
(d) Are aesthetically displeasing to
the neighbors.
6.114. A pure water plume disappears without
a trace. It evaporates and mixes in all direc-
tions in a wispy pattern.
6.115. Plumes containing both water and dust
will leave a trail of particulates after the
liquid water evaporates. One method of "read-
ing" these plumes in order to observe infractions
of equivalent opacity regulations is to observe
them at the point where the water vapor has
evaporated.
6.116. Other regulations specify that only
plumes containing "uncombined water" may be
neglected in enforcing equivalent opacity
regulations. Strictly speaking, this means
that the water plume can be read at the point
where it is most dense if it contains any
particulate matter.
6.117. Water plumes can be distinguished
from plumes of white particles in several ways:
(a) The wispiness of the plume as
it evaporates
(b) The greater frequency of occurence
and a greater length of plume
in cold, wet weather than in warm,
dry weather
(c) The detachment of the visible
plume from the top of the stack
in hot, dry weather, when it
takes the plume longer to cool
to its saturation point.
6,118. Water vapor can be emitted from
(a) Drying operations which re-
move water by evaporation
from foods, chemicals, de-
tergents, paper, pharmaceu-
ticals, ores, etc.
(b) Combustion in which hydrogen
containing fuels are used.
This is especially true of
natural gas combustion and
the burning of wet fuel.
(c) Air pollution control devices
which use water to remove the
gases or particulates from the
gas stream (for example, spray
chambers, spray towers, and
venturi scrubbers).
(d) Evaporation of water to remove
combustion or chemical reaction
heat from a process (for example,
forced and natural draft cooling
towers, operations for cooling
hot gases to protect pollution
control equipment, removal of
the heat generated in the ther-
mal process of producing phos-
phoric acid).
6.119. If visible wet plumes must be elim-
inated, several methods are available:
(a) Dilution of the plume by
mixing it with hot air
(b) Superheating the plume prior
to emission so that it will
disperse before it condenses
(c) Condensing the water out of
the plume by cooling it prior
to emission.
These are all expensive, however.
Suggested Additional Reading
Part B
Classification of Sources of Emission.
Opacity Problems Caused by Water Vapor.
Other
The Chemical Process Industries. R. N.
Shreve, Third Edition, McGraw-Hill,
New York, 1967, 905 pp.
Control Techniques for Particulate Air
Pollutants. NAPCA Publication No. AP-
51, 1969.
A-35
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Noncombustion Emissions and Water Vapor Plumes
Air Pollutant Emission Factors. M. J.
McGraw and R. L. Duprey, (revised
edition of NAPCA Publication No. AP-
42), 1971.
Air Pollution Engineering Manual, edited
by J. J. Danielson, DREW, PHS Publication
No. 999-AP-40, 1967.
Air Pollution Aspects of the Iron and
Steel Industry, J. J. Schueneman, M. D.
High, and W. E. Bye, DHEW, PHS Publica-
tion No. 999-AP-l, 1963.
Atmospheric Emissions From Sulfuric
Acid Manufacturing Processes. DHEW,
PHS Publication No. 999-AP-13, 1965.
Atmospheric Emissions From the Manu-
facture of Portland Cement. T. E. Krei-
chelt, D. A. Kemnitz, and S. T. Cuffe,
DHEW, PHS Publication No. 999-AP-17,
1967.
Atmospheric Emissions From Nitric Acid
Manufacturing Processes. DHEW, PHS
Publication No. 999-AP-27, 1966.
Atmospheric Emissions From Thermal-
Process Phosphoric Acid Manufacture,
NAPCA Publication No. AP-57, 1968.
Extractive Metallurgy. Principles and
Practices. W. H. Dennis, Pitman and
Sons, Ltd, London, 1965, 371 pp.
A-36
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VII. CLASSIFICATION AND IDENTIFICATION OF SOURCES
7.1. One reason for classifying sources is
to aid one in discussing their emissions of
pollutants. Measurements have been made of
the quantity and types of pollutants emitted
for a given amount of fuel or raw material
used in a process. Using these "emission
factors", the amount of pollutants emitted
from power plants, industry, automobiles, etc.,
can be estimated. The arranging of sources
into categories also makes it easier to point
out the similarities in plant appearance,
process equipment, and collection devices.
7.2. There are several categories into which
one can divide or subdivide air pollution sources.
(a) Mobile and stationary sources
(b) Point and area sources
(c) Combustion and noncombustion
sources
(d) Industrial, steam-electric,
residential, and commercial-
industrial sources
(e) Sources burning coal, oil, gas,
or wood versus sources not burning
fuel such as forest fires, agri-
cultural fires, or solid waste dis-
posal
(f) Reciprocal engines and continuous
combustion engines.
7.3. Point Sources are ones whose emissions
exceed some designated value (for example, 50
tons/year). Sources with smaller emissions can
be grouped together in some manner (for example,
all the residences in a certain square mile of
a city) to constitute an Area Source.
7.4. An example of a classification system
that includes all sources is
(a) Fuel Combustion in Stationary
Sources
(1) Industry
(2) Steam-Electric Power Plants
(3) Residential
(4) Commercial-Institutional
(b) Fuel Combustion in Mobile Sources
(1) Motor Vehicles
(2) Vessels
(3) Railroads
(4) Aircraft
(c) Industrial Process Losses
(1) Chemical Processing
(2) Food and Agriculture
(3) Metallurgical
(4) Mineral Products
(5) Petroleum Refining
(6) Pulp and Paper
(7) Solvent Evaporation and
Gasoline Marketing
(8) Other
(d) Solid Waste Disposal
(1) Municipal Incineration
(2) On-Site Incineration
(3) Open Burning
(e) Miscellaneous
(1) Forest Fires
(2) Structural Building Fires
(3) Coal Refuse Burning
(4) Agricultural
(5) Other
7.5. These categories can be subdivided
further, such as into point and area sources;
diesel and gasoline powered vehicles; jet
and piston-powered aircraft; and particular
types of .industries.
Identification
7.6. Without experience an inspector must
use various methods and clues to determine
the origin of the visible plumes he sees.
7.7. To learn the nature of the process,
he may use books from the library or other
sources describing manufacturing. Also
descriptive of the processes and the air
pollution arising from them are Federal
Government publications such as the AP series
of reports.
7.8. The inspector can learn about the
processes and their emissions by asking
questions of his associates and of plant
operators, by observing process operations,
and by taking photographs of manufacturing
operations and noting the similarities be-
tween types of operations.
7.9. Clues to the origin of emissions can
be obtained from
(a) The Company's name
(b) Directory of Manufacturers -
often published by Chamber of
Commerce of the city or by the
state
(c) Air Pollution files of per-
mits for construction or for
operation
(d) Surroundings of the source
such as objects sitting in
the yard. These might in-
clude the fuel used, the
raw materials, the products,
the waste material, and the
trucks for carrying out the
product
A-37
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Classification and Identification of Sources
(e) The shape of the building
housing the process
(f) Whether the source of emissions
is a stack or whether the emis-
sions consist of dust coming
out of the buildingcalled fu-
gitive dust
(g) Color of the plume
(h) Odor
(i) Effects on metal structures,
paint, vegetation, etc.
(j) Any collection devices for par-
ticles such as scrubbers, cy-
clones, electric precipitators,
baghouses, ponds, etc.
(k) Flares for burning waste gases
(1) Any equipment that is visible
such as furnaces, towers, rotary
driers
(m) Any variation of the plume during
the day or during the year which
might indicate start-up operations,
batch operations, or changes in
operation with weather; is it a
continuous process for 24 hours
a day or does it cease at the end
of the work day?
7.10. Many visible plumes are wholly or par-
tially condensed water vapor plumes. An in-
spector should be able to identify these since
they generally are not considered as violations
of visible emission regulations. Some sources
of water vapor plumes include
(a) Drying operations
(b) Combustion operations in which
the waste gases are discharged
at temperatures near the dew-
point
(c) Air pollution control equipment
which cleans the plume by spray-
ing it with water
(d) Operations in which heat is
removed by the evaporation
of water.
7.11. The inspector should be able to identify
the nature of the particulate, whether it is
dust, fume, smoke, mist, vapor, or gas.
7.12. If he knows what type of manufacture
is going on, then he should be able to identify
the possible component manufacturing processes
and their equipment.
7.13. The inspector should determine whether
the emissions are in the form of a
(a) A plume
(b) A cloud which has become
completely divorced from
its source
(c) A haze which exists over
a portion but not all of
a community indicating
that a local problem is :
present
(d) "Fugitive"'emissions which
do not come out of a stack
but from windows and other
openings in a building.
7.14. If the emissions are -in the form of
a plume, the inspector should note
(a) Whether the plume forms at the
top of the stack or a few feet
above the stack (a detached
plume)
(b) The body of the plume and how
far it rises before bending
over; its shape after it bends
over can be described as con-
ing, fanning, or looping
(c) The point at which it dissi-
pates; this may indicate
whether the emission is smoke,
fume, or contains water vapor.
A fume consists of relatively
heavier molten liquid droplets
which rapidly condense to a
solid or a mist at a dissipa-
tion point which is closer to
the stack outlet than in the
case of smoke particles. The
water vapor portion of a plume
may evaporate leaving particu-
late matter which persists for
a longer distance.
7.15. For smoke emissions, the color is
an indication of the type of combustion prob-
lem or,.the type of fuel:
(a) Black or gray smoke indicates
that the material is being
burned with inadequate air or
inadequate mixing of fuel and
air.
(b) White smoke indicates either
that the fire is being cooled
by excessive drafts of air or
that the materials being burned
contain excessive amounts of
moisture.
(c) Brown or yellow smoke indicates
the burning of a semi-solid
tarry substance such as asphalt
or tar paper. Generally, this
fuel has not been raised to a
temperature that is hot enough
A-38
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Classification and Identification of Sources
for best combustion and the
mixing with air is inadequate.
(d) Blue smoke often results from
the burning of trash which con-
sists of paper or wood products.
The plume is composed of small
liquid particles and contains
only a few particles of carbon
or soot.
7.16. The inspector should make an initial
identification of a visible plume by placing
it in one of the following classes:
(a) Emissions from stationary com-
bustion sources which are operated
to produce energy
(b) Emissions from mobile engines
(e.g., gasoline, diesel, jet)
(c) Emissions that are primarily or
totally water vapor
(d) Emissions of particulate matter
from industrial processes
(e) Particulate emissions accompany-
ing construction or demolition
(f) Emissions of visible gases
(g) Emissions from open-burning in-
cinerators, agricultural burning,
and structural building fires.
7.17. The air pollution control officer should
be familiar with all of the sources of emission,
the process equipment, and the control devices
which are located in his area.
(a) Sources of visible plumes
(1) Steam-electric'power plants
(2) Steam generating facilities
for institutions and schools
(3) Incineration equipment such
as tepee burners, single-
chamber and multiple-chamber
incinerators, etc.
(4) Furniture, lumber, and wood
products industry
(5) Cement plants
(6) Carbon black plants
(7) Soap and detergent manufacture
(8) Petroleum refineries
(9) Steel mills
(10) Asphalt batching plants
(11) Phosphate fertilizer manufacture
(12) Phosphoric acid manufacture
(13) Pulp and paper manufacture
(14) Lime plants
(15) Copper, lead, and zinc smelters
(16) Nitric acid manufacture
(17) Coke manufacture
(18) Gray iron foundries
(19) Vehicles powered by internal
combustion engines
(b) Manufacturing process equipment
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(12)
(13)
(14)
(15)
(16)
Furnaces
Kettles
Ovens
Cupolas
Kilns
Dryers
Roasters
Towers
Cookers
Digesters
Quenchers
Columns
Stills
Crucibles
Regenerators
Flares
(c) Air pollution collection devices
(1) Cyclones
(2) Baghouses
(3) Electrostatic precipitators
(4) Wet collectors
(5) Scrubbers
(6) Dry centrifugal collectors
(7) Venturi scrubbers
(8) Afterburners
(9) Fabric filters.
Suggested Additional Reading
Part B
Classification of Sources of Emission.
Other
Nationwide Inventory of Air Pollutant
Emissions-1968. NAPCA Publication No.
AP-73, 1970.
Control Techniques for Particulate
Air Pollutants. NAPCA Publication
No. 999-AP-40, 1967.
"Identifying Effluent Plumes", Air
Pollution Control Field Operations
Manual, edited by M. I. Weisburd,
PHS Publication No. 937, 1962.
A-39
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VIII. RINGELMANN CHART AND EQUIVALENT OPACITY
8.1. Regulations requiring that plume den-
sities or opacities not exceed a specified
standard are logical outgrowths of the ori-
ginal laws which prohibited "excessive or re-
pugnant smoke" as a nuisance. It was a nuisance
because it was "excessive or repugnant" to our
senses - sight, smell, and, possibly, touch.
Thus, an acceptable method of determining
whether a plume was a nuisance was to set an
emission standard based on visual determination
of the effluent how thick was the plume?
8.2. It has been shown that with proper
training an inspector can evaluate the dens-
ity or opacity of a plume within 5 to 10 per-
cent of the correct value as determined by
optical instruments. When his training is
supplemented by periodic retesting, the in-
spector can maintain his plume reading pro-
ficiency. On this basis the courts have
upheld the Ringelmann and Equivalent Opacity
regulations when they are enforced by qualified
personnel.
8.3. Maximum emission standards can relate
to grain or dust loading as well as optical
density or opacity. Compliance with the
latter type is easier and cheaper to check.
It requires only that an inspector make an
observation for a specified time period.
8.4. Although the visual standard is limited
to estimations of particles of pollution which
obscure vision, its application simultaneously
tends to reduce the total weight of all sizes
of particles emitted. Thus, the visual emis-
sions standard can supplement the grain loading
standard and help to reduce the number of source
tests the latter standard would require.
8.5. In order to comply with the opacity
standard, more efficient equipment operation
or more efficient combustion is required of
a pollution source. A general theoretical
relationship between plume opacity and par-
ticulate mass concentration for several types
of particles (carbon, liquid water, and iron
oxide) has been developed.
8.6. An inspector's knowledge of the size
distribution of particle sizes and weights
found in the stack tests of various types of
stokers, oil burners, manufacturing processes,
etc., may serve as a guide to the relation
between opacity and mass of effluent. If 75
percent of the weight of a plume is in par-
ticles whose sizes are larger than 5 microns
in diameter and only 10 percent is in parti-
cles whose diameters are less than 1 micron,
then the portion which is scattering light
(0.4 to 0.7 micron) is small. Under these
circumstances, compliance with the visual
standard may not insure compliance with the
dust loading standard.
8.7. The Ringelmann chart was developed
about 1890 by Maximilian Ringelmann, a pro-
fessor of agricultural engineering in Paris.
It was introduced into the United States in
1897 and first incorporated into law in
Boston in 1910.
8.8. The chart is a method of judging the
shade of gray of a given smoke plume and was
originally applied to the emissions from
coal-fired boilers.
8.9. Many regulations state that is illegal
to emit smoke of a darker shade than Ringel-
mann No. 2 for more the 3 minutes in an hour.
This 3-minute grace period is allowed for
starting up or soot blowing.
8.10. The State of California through its
Air Pollution Control Districts in 1947 ex-
tended visual emission standards beyond the
use of the Ringelmann chart for gray-black
plumes. It also prohibited a plume of any
color if the plume's opacity was greater
than Ringelmann No. 2.
8.11. While there are actually two regu-
lations which cover all plumes, both black
and nonblack, one regulation could be suf-
ficient for regulating the opaqueness of any
plume. However, the Ringelmann standard
historically was established first and the
equivalent opacity standard was referred to
the Ringelmann Chart. Actually, the inspec-
tor generally judges the amount of light
transmitted through both black and nonblack
plumes and then relates this transmission to
Ringelmann Numbers as a measure of the smoke
density of gray-black smoke and equivalent
opacity percentages for colored or white
plumes. If he compares the gray-black plume
with a Ringelmann Chart, he is equating the
60 percent of light transmitted through a
No. 2 plume with the 60 percent of light
reflected by the No. 2 Ringelmann Card. The
term "equivalent opacity" refers to the ex-
tension of the Ringelmann Chart to judge the
degree to which a visible plume of any color
obscures the view of the observer. The state-
ment of the equivalent opacity regulation
generally includes a clause stating "such
opacities as to obscure an observer's view to
a degree equal to or greater than does smoke
of Ringelmann No. 2 shade".
8.12. The definitions of the terms "smoke
density" and opacity are the source of much
controversy and confusion by defense attorneys
attempting to invalidate the entire smoke-
reading procedure. The definitions of these
terms as they apply to visible emissions are
(a) Smoke Density - One definition
of density is "the quantity per
unit volume or area". Another
A-40
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Ringelmann Chart and Equivalent Opacity
is "the mass of a substance per
unit volume". In visual emission
usage the first definition is the
correct one. When applied to the
Ringelmann Chart, density refers to
the ratio of the area occupied by the
black grid line to the total area
of each card. Since these grid lines
are opaque areas, the smoke density
is compared with opacity. The defi-
nition is not meant to refer to the
weight per unit volume of the plume.
(b) Opacity - Opacity means the degree
to which transmitted light is ob-
scured. In air pollution the expert
reader judges the amount of back-
ground, sky, or light that he
cannot see through the emission.
The Ringelmann Chart
8.13. The Ringelmann system is a method of
reproducing shades of gray by means of a rec-
tangular grid of black lines having fixed widths.
When these grids are viewed from a distance, they
appear to form a uniform gray area.
8.14. There are five equal steps between
white and black. The grid lines are 10 mm
apart for each card. The specifications for
the square spaces between the grid lines are
(a) Card 0 - all white (100 percent
of the light transmitted)
(b) Card 1 - black lines 1 mm thick,
white spaces 9 mm square (81
square mm) - 80 percent trans-
mission
(c) Card 2 - black lines 2.3 mm thick,
white spaces 7.7 mm square (59
square mm) - 60 percent trans-
mission
(d) Card 3 - black lines 3.7 mm thick,
spaces 6.3 mm square (40 square
mm) - 40 percent transmission
(e) Card 4 - black lines 5.5 mm thick,
white spaces 4.5 mm square (20
square mm) - 20 percent trans-
mission
(f) Card 5 - all black - 0 percent
transmission.
Since the accuracy required of the chart will
not be 1 percent of less, the differences be-
tween 59 percent and 60 percent can be considered
negligible.
8.15. The Ringelmann Chart published by the
Bureau of Mines is the chart which is referenced
in air pollution law. This chart provides the
shades of Cards 1, 2, 3, and 4 in a single sheet.
These are known as Ringelmann No. 1, 2, 3, and
4, respectively.
8.16. If the chart is used while observing
smoke, it should be mounted 50 feet from the
observer at which distance the lines on the
chart merge into shades of gray. The ob-
server glances from the smoke, coming from
the stack, to the chart and notes the number
of the card that most nearly corresponds with
the smoke shade. When the correspondence is
not exact, the reading can be made to the
nearest 1/4 Ringelmann Number. A clear stack
is recorded as No. 0 and 10 percent black
smoke is recorded as No. 5.
8.17. With proper experience during a
training period, an observer can fix the
shades of the Ringelmann Chart in his memory.
The inspector may then make his observations
in the field without having a chart with him.
The Superior Court of Los Angeles has compared
this to one's not needing "a color chart in
his hands to recognize a red flower, a blue
sky, or a black bird".
Smoke Reading Aids
8.18. Although a number of smoke reading
aids have been developed to assist in measu-
ring the Ringelmann number of gray or black
smoke, none have the versatility of a trained
inspector under varying conditions.
8.19. Smoke Tintometer - This instrument
uses tinted glasses graduated to the Ringel-
mann scale for comparison with the smoke. It
contains two apertures, one for observing
the smoke and one for viewing the clear sky
through the opening or through one of the
tinted glasses.
8.20. Umbrascope - This is a tube using
tinted glass segments which cover one-half
of the field of view. The smoke is seen
through the other half of the field and is
compared with the opacity of the glass. One
thickness of the gray glass gives 60 percent
opacity and is equivalent to Ringelmann No.
3. Additional thicknesses of glass give even
greater opacity. Thus, no opacity less than
60 percent can be measured with this instru-
ment.
8.21. Smokescope - This instrument con-
sists of two barrels for receiving incoming
light and one eyecup for viewing. The stack
is viewed through one barrel of the instru-
ment. Light from an area adjacent to the
stack enters the other barrel and illuminates
a circular standard density film. Half of
this film is equivalent to No. 2 Ringelmann
and the other half is equivalent to No. 3
Ringelmann. The image of these two half
disks is projected onto a screen in front
of the eyecup and this image surrounds a
small aperature where the smoke is seen.
A-41
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Ringelmann Chart and Equivalent Opacity
The observer then compares the smoke shade with
the two Ringelmann shades. The advantage of
this instrument over a Ringelmann Chart used
in the field is that the illuminations of the
smoke and the reference are both influenced by
the same factors. One is not transmitted light
while the other is reflected. Thus, the smoke-
scope is automatic compensation for varying
light conditions.
8.22. Film Strip - This is called a Smoke
Inspection Guide and consists of four densi-
ties, 20 percent, 40 percent, 60 percent, and
80 percent transmission. The inspector views
the source and matches it as closely as possible
with one of the densities on the guide.
8.23. Smoke Comparison Charts - Several
charts are available and all of them work on
the Ringelmann principle. They have shades
of gray corresponding to Ringelmann Numbers
1, 2, 3, and 4 printed on a small, pocket-
sized card which the inspector can carry with
him. When making comparisons with a plume
the inspector should hold the card at arm's
length.
8.24. Photoelectric Cells - Photoelectric
smoke-metering equipment may be permanently
built into a stack. This device measures
variations in the intensity of a beam of
light passing through the effluent in the
stack. As part of the granting of a permit,
these may be required to be mounted on a
stack for continuously monitoring the emissions.
In these devices, a constant light source is
used to illuminate a standard photoelectric
cell that is located on the opposite side of
the stack. The light must pass through any
smoke rising in the stack before it reaches
the cell on the opposite side. The photo-
electric cell produces a current of electri-
city which is directly proportional to the
amount of light falling on the cell.
The main problem with most of these devices
is in trying to periodically zero the photo-
cell, especially in continuously operating
stacks. Emission buildup on the light source
and on the photocell also creates a problem.
8.25. All of these smoke-reading aids ex-
cept the photoelelectric cell can be used only
with the black-gray plumes. There are no aids
of this nature for assisting the inspector in
judging those plumes which fall under the
equivalent opacity regulation.
8.26. The Smoke Reading Aids are sometimes
cumbersome and are generally not significantly
more accurate than sight reading in establishing
opacity violations.
8.27. The lidar (or laser radar) instru-
ment has been proposed as a method of measu-
ring smoke-plume opacity. The lidar is com-
posed of a laser transmitter which emits a
very brief, high-intensity pulse of coherent
light and a receiver which detects the por-
tion of this light which is back-scattered
to the instrument from the aerosols in the
atmosphere. When plume opacity is measured,
the lidar light is shot through the plume and
is scattered backward by the aerosols on the
other side of the plume. The receiver mea-
sures the amount of reduction in the inten-
sity caused by the two passages of the light
through the plume. At present, this instru-
ment is still quite expensive for routine
usage.
Training of Inspectors
8.28. Enforcement agencies have found it
possible to train observers to recognize
Ringelmann numbers and percent opacities
without having a comparison chart before
them. The inspectors are taught to judge
the plume shade or opacity by relating it to
percent of light transmission of a training
plume. The training plume is generated by
special equipment which regulates the opacity
of the plume and measures the opacity by a
photocell arrangement in the stack of the
generator.
8.29. Training with the smoke generator
begins by familiarizing the students with
known densities of black and white smoke.
Upon the sound of a horn the instructor calls
out the meter reading. He will go up and
down the Ringelmann and Equivalent Opacity
scales.
8.30. Next, the students, are given a prac-
tice run of 25 black and 25 white shades of
smoke. At the completion of this run, a
student can grade his performance and deter-
mine whether he was reading high or low.
8.31. After these familiarization and
practice runs, the students are ready for
testing for record. Repeated runs of 25
white and 25 black shades of smoke are made
with the smoke generator. In between test x
runs, short familiarization runs may be made
to reinforce the student's accuracy of judge-
ment.
8.32. A student keeps on observing the
testing runs until he qualifies as an expert
smoke reader. The requirements are that he
must have an average deviation on white
A-42
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Ringelmann Chart and Equivalent Opacity
and black smoke combined of not more than 7.5
percent and that no reading may vary from the
actual value by 1 Ringelmann of 20 percent
opacity aver the set of 50 readings.
8.33. Additional training may be allowed if
the student does not meet the standards. How-
ever, if the student is unable to pass the vis-
ible emissions test, he can be disqualified
from serving as an inspector.
8.34. Training runs may be conducted under
a variety of conditions of lighting and back-
ground color to simulate actual field condi-
tions.
8.35. To evaluate plumes at night it is
necessary to have a source of light behind the
plume and to evaluate the transmission of this
light through the plume. Nighttime readings
should be made a part of the training program
if the inspector will be required to make
field evaluations at night as part of his
duties.
8.36. Readings can also be made of smoke
from tailpipes or exhausts of moving vehicles.
The observer should
(a) Read the smoke at its point of
maximum density
(b) Use a stopwatch to record the
accumulated violation time
(c) Avoid reading directly into the
plume, if possible; it may be
difficult to have a wide angle
between his line of sight and
the line of exhaust smoke
(d) Take a photograph of the offending
vehicle and its plume.
Problem of Reading Smoke in the Field
8.37. There are several criticisms of visible
emission control regulations and the ability of
inspectors to enforce them objectively. Many
of these criticisms can be overcome by the in-
spector's following of proper procedures in
his field observations.
8.38. Criticism: The opacity or smoke den-
sity observation made by an inspector will vary
with his position in relation to the sun and
sky, the atmospheric lighting, the background
of the plume, and the size of the particles in
the plume.
Response: The inspector should strive to
make his observations with the sun at his back,
with the wind blowing at right angles to his
line of sight, and with a background which con-
trasts with the color of the plume. Multiple
observations under varying atmospheric con-
ditions can also be made to reduce the effects
of the background and atmospheric lighting. An
experienced observer can learn to weigh the
opacity conditions in relation to various con-
ditions.
On the other hand, wide variations of the
sizes of particles in a plume will affect the
light-scattering potential of the plume.
8.39. Criticism: Opacity and smoke-density
measurements have not been correlated with
other measurement methods.
Response: For two types of particles, D. S.
Ensor and M. J. Pilat have developed a relation-
ship between plume opacity and a combination of
the following properties: plume diameter, par-
ticle size distribution, particle mass concen-
tration, average particle density, and particle
refractive index. Thus, their equation includes
more variables than plume opacity and mass of
emissions; however, if certain assumptions are
made, predictions of plume transmittance can be
related to particulate mass concentration.
The observer should have a knowledge of the
processes emitting a visible plume so that he
can make a judgement of how normal its appear-
ance is. Its appearance may vary with the
sequence of startup operations or with the
atmospheric relative humidity.
It is reasonable to assume that the elimina-
tion of visible emissions will reduce dust and
aerosol emissions; however, the reduction may
not be in the same ratio. The small particles
between 0.1 and 1 micron which cause the light
scattering require more expensive control equip-
ment than the large particles (greater than 10
microns), which obscure light by absorbing it.
8.40. Criticism: Gaseous emissions cannot be
determined by visible observations.
Response: Very few gases are visible so the
visible emission regulations can constitute
only a portion of a full set of air pollution
regulations.
The opacity of a reddish-brown plume of nitro-
gen dioxide gas will indicate the amount of that
pollutant that is being emitted from a process.
A bluish plume for a boiler burning fuel oil
will be an indication of the high sulfur con-
tent of the oil.
8.41. Criticism: Visible-emission observa-
tions are difficult to apply at night.
Response: If the observer positions himself
so that there is a source of light behind the
plume or places an auxiliary light source
behind a plume, then he may make readings at
night.
A-43
-------
Ringelmann Chart and Equivalent Opacity
8.42. Criticism: A wet plume may be judged
as opaque although its opacity is really due to
the water droplets which are not considered as
pollutants.
Response: Since water is not normally con-
sidered as an air pollutant, some allowance
must be made for those visible plumes whose
opacity is derived from uncombined water
droplets. One method is to require that
opacity readings of a wet or steam plume be
taken at that point of the plume where the
steam has evaporated. If the inspector sus-
pects that the source is in violation, it may
be necessary to wait for a hot, dry day when
the steam rapidly dissipates. He can then
make his observation closer to the stack.
8.43. Criticism: Visible-emission regula-
tions can be circumvented by a polluter if he
adds more air to his effluent or builds a new
stack of smaller diameter for emitting the
same quantity of effluent.
Response: The adding of auxiliary air to the
effluent in the stack will reduce the concen-
tration of the pollutant and will reduce the
opacity of the plume.
By decreasing the radius of the stack, the
distance through the plume will decrease and,
since the velocity of the emission increases,
the concentration of the effluent through the
plume will remain the same. The result is
that since the light will pass through a
thinner plume, less light will be scattered
and the observer will read a lower opacity.
A narrower stack may not fall under the
circumvention clause. In this case it may be
necessary to order a source test to determine
if there is a violation of a process weight,
emission weight, or grain loading ordinance.
The adding of air to the plume to obtain a
lower concentration is specifically prohibited
in "circumvention" clauses of some regulations.
These prohibit the building and operation of
equipment that tends to conceal the emission.
It is also possible that the most opaque
portion of the plume may occur at some dis-
tance above the stack where the emission loses
its buoyancy. The best time for observing
such a condition would be a day with little
or no wind.
Advantages of Visible Emission Regulations
8.44. Observers can be trained in a relatively
short time and it is not necessary that observers
have an extensive technical background.
8.46. No expensive equipment is required.
8.47. Violators can be cited without re-
sorting to time-consuming and costly source
testing. A particulate source test takes a
minimum of 1 day for a single stack plus the
time needed for laboratory analysis and re-
port writing at a minimum cost of $1,000 per
source.
8.48. Questionable emissions can be loca-
ted and then the actual emissions determined
by source tests, if necessary.
8.49. Control can be achieved for those
operations not readily suitable to regular
source testing methods, such as leakage from
equipment and buildings; loading of grain,
coal, and ores; or visible automobile or
truck exhaust.
Suggested Additonal Reading
Part B
Standards for Particulate Emissions.
Techniques for Visual Determination.
Equivalent Opacity.
Reading Visible Emission.
Other
8.45.
a day.
One man can make many observations in
"Ringelmann Smoke Chart", U.S. Dept.
of the Interior Information Circular
8333, 1967.
Optical Properties and Visual Effects
of Smoke Stack Plumes. W. D. Conner
and J. R. Hodkinson, DHEW, PHS Publi-
cation No. 999-AP-30, 1967.
"Plume Opacity and Particulate Mass
Concentration", M. J. Pilat and D. S.
Ensor, Atmospheric Environment, 1970
Vol. 4, pp. 163-173.
"Calculation of Smoke Plume Opacity
From Particulate Air Pollutant Pro-
perties", D. S. Ensor and M. J. Pilat,
Paper presented at 63rd Air Pollution
Control Association Meeting in St.
Louis, Missouri, June, 1970.
"The Relationship Between the Visibility
and Aerosol Properties of Smoke Stack
Plumes", D. S. Ensor and M. J. Pilat,
Paper presented at the Second Interna-
tional Union of Air Pollution Prevention
Associations in Washington, B.C., Decem-
ber, 1970.
A-44
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IX.
QUALIFICATION PROCEDURES AND EXCERCISE
IN RECORDING FOR QUALIFICATION
9.1. The proficiency test requires the in-
spector to observe 25 shades of black smoke
and 25 shades of white smoke.
9.2. To qualify, the inspector must read
each shade with no deviations equal to or
greater than 20 percent opacity or 3/4 of a
Rlngelmann number. His average deviation
from the correct readings must be less than
10 percent for the white smoke and less than
1/2 Ringelmann (equivalent to 10 percent) for
the black smoke.
9.3. The field portion of this course con-
sists of reading series of 25 black and 25
white shades of smoke produced by the smoke
generator.
9.4. There will be some familiarization runs
of both black and white smoke during which the
opacity or Ringelmann number will be announced
while the smoke is being emitted.
9.5. There will then be a practice run of
50 smoke emissions. Twenty-five black shades
will be run followed by 25 white shades, or
vice versa. The student will record his
observations in whole or fractional Ringelmann
numbers and percent equivalent opacity. At
the conclusion of the 50 emissions, the student
will compare his readings against the trans-
missometer readings, record his deviations, and
compute his average deviation.
9.6. Following the practice run there will
be repeated runs of 50 emissions during which
the student will try to refine his smoke-
reading ability until he meets the requirements
of average deviation less than 10 percent (or
1/2 Ringelmann) and no reading equal to or
greater than 20 percent opacity (or 3/4 Ringel-
mann) .
9.7. A Smoke School Training Form will be
used to record the readings and deviations and
to compute the information required for quali-
fication. It also has spaces for information
regarding the observer, the time of day, the
weather, and the observer's position in rela-
tion to the wind direction, the sun, and the
background for the smoke.
9.8. This form must be filled in completely
when it is submitted to the examiner by the
student who has qualified on a series of emis-
sions.
Instructions to the Student
During the Reading of Smoke
9.9. The aim of the training and testing
of smoke readers in this course is to pro-
duce an inspector whose judgement of plume
density will be accurate and unaffected by
variable field conditions. His expert ob-
servations serve in place of the measurements
of a mechanical device and his accuracy must
stand up of the case is brought to court.
9.10. To aid the accuracy of inspectors
and to promote the uniformity among inspec-
tors' readings, several rules of smoke reading
should be followed while the smoke reader is
making his observations:
(a) The sun should be behind the
observer during daylight hours.
This avoids the problems arising
from the forward scattering of
light by the.particles in the
plume.
(b) The light source should be
behind the plume at night.
(c) Readings should be made at
right angles to the wind di-
rection, and from any distance
necessary to obtain a clear
view of the stack and back-
ground. This might be from 100
feet to 1/4 mile in the case of
stacks in the field but not
closer than 50 feet in the case
of observing the plumes from
the smoke generator.
(d) For plumes not containing water
vapor the inspector should esti-
mate the plume density at a point
only a foot or two above the
stack at which height the plume
is no wider than the diameter of
the stack. The inspector should
make his observations of water
vapor plumes in accordance with
local ordinances.
(e) The inspector should try to
read the plume against a con-
trasting background such as
blue sky for black plumes and
tree leaves for white plumes.
(f) The inspector should not stare
at the plume, but should look at
it only at prescribed intervals
such as every 15 seconds or 60
seconds. Staring at the plume
will cause fatigue and produce
erroneous readings.
A-45
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Qualification Procedures and Exercise
9.11. During the inspector's training and
testing with the smoke generator, a horn will
be sounded when he should look at the plume
and make his observation. In between the
soundings of the horn he should not stare at
the plume. The time interval between the
sounding of the horn and the glancing at the
stack top by the observer is approximately
the time it takes the generator smoke to tra-
vel from the generator's transmissometer to
the top of the stack.
9.12. If this local agenpy permits it, the
inspector may use small, hand-held Ringelmann
Charts or other aids as guides in judging the
black and gray shades.
9.13. The inspector should not wear dark
glasses while taking the test unless he plans
to wear these glasses while making smoke read-
ings in his normal enforcement and inspection
duties.
Filling Out the Training Form
9.14. Name and Affiliation of the observer
are self-explanatory, as is the Date of the
test.
9.15. The Time should be the approximate
time when the switch between black and white
smoke was being made.
9.16. Location refers to the address and
city where the test was given.
9.17.. The Wind Speed should be estimated
by the observer within a 3 to 5 mile-per-hour
range. If an anemometer (wind speed instrument)
is not available, he may estimate the wind speed
by using the Beaufort wind scale.
9.18. To determine the Wind Direction the
observer must first know his orientation with
respect to north. This can be learned from a
map. The direction from which the wind is
blowing can then be estimated to 16 points of
the compass (N, NNE, etc.) by watching a flag
or seeing which way a handful of grass blows
when thrown into the air.
9.19. Sky Condition should be filled in as
(a) Clear - less than 0.1 of the
sky covered by clouds
(b) Scattered - 0.1 to 0.5 of the
sky covered
(c) Broken - 0.5 to 0.9 of the
sky covered
(d) Overcast - more than 0.9 of the
sky covered.
9.20. Observer's Position should show his
position in relation to the sun, the smoke
generator, and the plume.
9.21. Run No. - Each run during the train-
ing session will consist of 25 black (B) and
25 white (W) shades of smoke. The runs will
be numbered successively beginning with 1-B
and 1-W.
9.22. The students will enter his observa-
tions in the Observer's Reading columns. The
black smoke readings should be entered as
fractions of Ringelmann Numbers, with 0 being
the lowest and 5 being the largest. The mini-
mum increment is 1/4. The white smoke read-
ings should be entered in percent opacity.
The lowest possible reading is 0 and the high-
est is 100. The observations are made to the
nearest 5 percent.
9.23. At the end of the run the instructor
will read off the transmissometer readings and
the student should enter these values in the
Transmissometer Reading columns.
9.24. The student will then fill out the
+ Deviation column. If the observer's reading
is less than the transmissometer reading, the
difference is entered in the - Deviation column.
9.25. In computing the deviations for the
black smoke readings, it will be more conveni-
ent to convert the fractional Ringelmann num-
ber differences into percents, similar to the
white smoke. A deviation of 1/4 Ringelmann
is equivalent to 5 percent, 1/2 to 10 percent,
3/4 to 15 percent, 1 to 20 percent, and so on.
As can bee seen, these conversions to per-
centages are done by multiplying the Ringel-
mann deviations by 20.
9.26. The entries in the + Deviation and -
Deviation columns are added and their Sum is
entered at the bottom of the column. The
Number of deviations in each column is also
entered at the bottom of the column. These
entries can be used by the student to guide
him as to whether he is tending to read high
or low. If he divides the sum of his devia-
tions by the number of deviations, he can
estimate how high or low he is reading.
9.27. In the QUALIFICATION portion of the
form, the two sets of boxes refer to the
black and white portions of the run.
9.28. In the first set of boxes enter the
run number.
9.29. In the second set of boxes, enter
the number of readings on which the observer
agreed exactly with the transmissometer read-
ing.
A-46
-------
Qualification Procedures and Exercise
9.30. In the third set of boxes, enter the
number of readings on which the observer dis-
agreed with the transmissometer by a whole
Ringelmann Number or more (black) or by 20
percent or more equivalent opacity (white).
9.31. Calculate the average deviation on
both the black and white portions of the run
by adding the sum of the + Deviations to the
sum of the - Deviations and dividing this by
the number of readings (25).
9.32. The Examiner will verify the Training
Forms of those students who will qualify.
9.33. To qualify, the student must have no
readings of black or white smoke which deviate
by a whole Ringelmann Number or 20 percent
equivalent opacity and his average deviation
for white and for black smoke must be less
than 10 percent.
9.34. A modified training form of 5 black
and 5 white readings is shown as an example.
Suggested Additional Reading
Part B
Reading Visible Emissions.
Other
"Reading Visible Emissions", Air Pollu-
tion Control Field Operations Manual.
edited by M. I. Weishurd, PHS Publica-
tion No. 937, 1962.
A-47
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X. BASIC METEOROLOGY
Radiation. Stability, and Inversion
10.1. The incoming radiation from the sun
supplies the energy for the earth. This
energy heats the earth and atmosphere and
helps drive the winds.
10.2. The sun's energy is transmitted to
the earth in many wavelengths (e.g., ultra-
violet, infrared, X-rays, radar waves) but
the majority of it arrives in the wavelengths
which are visible to human eyes, 0.4 micron
to 0.7 p..
10.3. When the sun's rays reach the earth
and its atmosphere they are either reflected,
absorbed, scattered, or transmitted. They can
be reflected by smooth snowy surfaces, smooth
water surfaces, and cloud tops. They can be
absorbed by the earth or by water vapor, gases,
dust, or particulates in the air. They can be
scattered by small particulates in the air such
as smog, haze, and mist particles.
10.4. When the skies are clear, about 70
percent of the sun's radiation which reaches
the upper atmosphere of the earth is trans-
mitted to the surface and absorbed. Under
overcast conditions only about 35 percent of
the radiation gets through.
10.5. The earth's surface loses heat by
radiation, conduction to the air near the
surface, and convection within the water on
the earth.
10.6. The energy radiated from the earth is
not in the wavelengths visible to the human eye.
However, it is in a wavelength which is absorbed
by water vapor. Thus, this radiation is absorbed
by the clouds and water vapor in the air and
part of the radiation is sent back towards the
earth. This "greenhouse effect" helps to keep
earth warm, even when the sun is not shining.
The moon has no atmosphere or water vapor, there-
fore its surface is very cold where the sun is
not shining.
10.7. The heat conducted from the earth's
surface to the air adjacent to the surface is
subsequently transferred to the air above by
convection currents. Since the earth's sur-
face is the main source of heat for the air
within 5 or 6 miles of the surface, the tempera-
ture on the average, decreases with height in
this layer.
10.8. The change of temperature with height
in the atmosphere is called the lapse rate of
temperature.
10.9. The wind and lapse rate of temperature
control the dispersion of a plume into the atmo-
sphere.
10.10. Winds which vary their direction
spread a plume out over a wide angle.
10.11.
faster.
Stronger winds dilute the plume
10.12. Stronger winds also cause the plume
to bend over into the horizontal faster and
reduce the effective stack height.
10.13. The effective stack height is the
distance from the ground to the level at
which the center of the plume becomes hori-
zontal the sum of the actual stack height
and the plume's rise above the stack.
10.14. Factors that increase the plume
rise and the effective stack height are the
exit velocity of the plume from the stack and
the difference in temperature between the
plume and the air at the top of the stack.
10.15. The lapse rate of temperature de-
termines the stability of the atmosphere.
When the atmosphere is very stable the plumes
spread out sideways and vertically very slowly.
When the atmosphere is very unstable, the
plume spreads out or disperses rapidly.
10.16. When the temperature decreases up-
ward at 5.4 F/1000 feet, the atmosphere has
neutral stability and the plume spreads out
like a cone. This particular lapse rate of
temperature is called the "dry adiabatic"
lapse rate.
10.17. If the temperature decreases with
height at a much slower rate than the dry
adiabatic rate or if the temperature stays
the same with height or if it increases with
height, the atmosphere is stable and the
plume does not spread out vertically although
it may "fan" out in the horizontal.
10.18. If the temperature decreases with
height at a greater rate than the dry
adiabatic rate, the plume will "loop" up-
watd and downward.
10.19. Temperature Change With Height
Change With Height Lapse Rate
(a) Decreases at 5.4 F
per 1000'
(b) Decreases faster
than 5.4 F/1000'
(c) Decreases slower
than 5.4 F/1000'
(d) No change with
height
(e) Increases with Inversion
height
Stability Type
Dry adiabatic
Superad iabat ic
Subadiabatic
Isothermal
Neutral
Unstable
Slightly
stable
Stable
Very
stable
A-48
-------
Basic Meteorology
10.20. The types of temperature inversions
important in air pollution are the nocturnal
or radiation inversion and the subsidence in-
version.
10.21. The nocturnal inversion forms at
night when the ground cools off by radiating
its heat outward to space. How deep and strong
this inversion is depends upon the wind speed
and the rate of cooling of the surface.
10.22. The wind must be light (less than 5
mi/hr) for an inversion to form. Strong
winds will mix the air and maintain a tempera-
ture decrease with height. A lack of any wind
will cause the inversion to be very shallow
but very pronounced, since the exchange of
heat between the air and the ground will be
very slow.
10.23. The nocturnal inversion will not form
or will be weak if the nighttime sky is cloudy.
The clouds will absorb the radiation and re-
radiate it back to earth, keeping the air warm
in the lower levels.
10.24. If the air is moist, a fog will form
with the nocturnal inversion. It will not
form with strong winds and if there is no wind,
only dew or waist-high fog will form.
10.25. The depth of a radiation inversion
grows as the night proceeds. It may reach
1500 to 2000 feet in depth. Thus, depending
on circumstances, its top may or may not be
higher than the height of a smoke plume.
10.26. In the morning, a radiation inversion
is broken up by the heat of the sun which warms
the ground. The heat is convected upward
higher and higher into the air until it reaches
the top of the inversion. During the process
the inversion layer is elevated and does not
extend to the ground.
10.27. The morning inversion breakup will
change a fanning plume into a fumigation
situation when the convective currents reach
the height of the plume. The plume will be
spread downward rapidly during a period of
about half an hour during fumigation.
10.28. A subsidence inversion is an elevated
inversion the base of which is generally be-
tween 4000 and 6000 feet above the ground. It
is formed when a layer of air slowly sinks and
warms to a temperature higher than the air be-
low.
Weather Maps
10.29. A weather map will depict some or
all of the following:
(a) Lines of constant atmospheric
pressure - "isobars"
(b) Low pressure areas - "lows"
or "cyclones"
(c) High pressure areas - "highs"
or "anticyclones"
(d) Fronts
1. Cold.
2. Warm
3. Stationary
4. Occluded.
10.30. Fronts separate masses of cold and
warm air. The warm air slants above the cold
air with height. If the warm air is advancing,
it is a warm front. If the cold air is ad-
vancing, it is a cold front. Sometimes one
front will overtake another one to form an
"occluded front".
10.31. Generally, there is a high-pressure
area shown in the warm- and in the cold-air
masses. Also, the fronts are generally shown
extending out of low-pressure areas; frequently,
a low-pressure area has both a cold and a
warm air front attached to it.
10.32. From day to day, the fronts and
pressure areas will move from west to east.
The cold fronts may move southeast and the
warm fronts northeast.
10.33. The highs and lows have the follow-
ing distinguishing characteristics:
High-pressure area
(a) Winds flow outward from a
high in a clockwise direction
(b) Air sinks creating a subsidence
inversion
(c) Low relative humidity, few
clouds, little precipitation,
sunny skies
(d) Low wind speeds, variable wind
direction
(e) Nocturnal inversions likely
(f) System covers a large area
(g) System moves slowly and may
remain stationary for several
days.
A-49
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Basic Meteorology
Low-pressure area
(a) Winds flow inward toward a
low in a counterclockwise
direction
(b) Air rises giving good dispersion
(c) High relative humidity, cloudy,
precipitation likely
(d) High winds likely
(e) Inversion development unlikely
(£) System covers small area
(g) System moves rapidly.
Particles in the Air and
Obstructions to Visibility
10.34. The sizes (diameters) of the particles in
the plume or in the air determine how they are
removed and what the visibility is.
10.35. Particles can be removed by gravita-
tional settling, impaction on large objects,
rainout by having raindrops form around them,
or washout by being captured by falling rain-
drops .
10.36. Gravitational settling is most impor-
tant for particles whose diameters are larger
than 20 p,. The settling will occur within short
distances of the source.
10.37.
to 20 p,.
Impaction affects particles below 10
10.38. The particles forming nuclei for
raindrops and those being removed by rainout
are 0.2 p, and larger.
10.39. Particles which are greater than 1 p.
and which are in the area of rain will be washed
out.
10.40. Particles below the rain clouds but
smaller than 1 JJL will be removed by the rain if
they absorb some of the water vapor and grow to
a size greater than 1 p,.
10.41. Small particles whose size is the same
as the wavelengths of visible light (0.4 to 0.7
p,) cause this light to be scattered when they
are suspended in the air.
10.42. This scattering causes a decrease in
the visual range the distance one can see.
10.43. When the light is scattered, more is
scattered forward than backward. Thus, in a
hazy atmosphere one can see objects more dis-
tinctly when one has the sun at his back than
when one is looking toward the sun.
10.44. This decrease in visual range is due
to dry haze, damp haze, and mist.
10.45. Dry haze is composed of fine dust or
particles less than 0.1 p, in diameter. When
moisture condenses on the haze particles, they
grow and become damp haze (diameters of 0.1 to
1.0 p.). Mist is a thin, grayish veil that is
present when the relative humidity is greater
than 95 percent. Its droplets are interme-
diate between damp haze and fog.
10.46. Haze is confined to a haze layer,
which is usually bounded at the top by a
temperature inversion. The haze layer may
be several hundred feet deep at night and
several thousand feet deep in daytime. It
may exist only over an urban area or it may
cover thousands of square miles coincident
with a stable high pressure area.
Clouds and Fog
10.47. There is always some water in the
air. If it is in the gaseous state, it is
called water vapor and is invisible.
10.48. Clouds and fog are composed of small
liquid water drops. High clouds contain
frozen droplets.
10.49. The larger liquid or solid water
particles fall out as rain, snow, hail, etc.
10.50. The warmer air is, the more water
vapor it will contain. As more water is added
to the air or as the temperature cools, the
relative humidity reaches 100 percent. After
that point, any more water added or any more
cooling causes the excess water vapor to con-
dense into liquid water drops which are visible.
10.51. The air may contain the same amount
of water vapor day and night, but the cooling
at nighttime may reduce the air temperature
to its dewpoint so that condensation occurs
and fog or dew appears.
10.52. Clouds are often formed when moist
air is lifted upward toward the cooler tem-
peratures. This lifting can occur as the air
slides up over the colder air at a front or
as the air heated at the earth's surface is
carried upward by convection currents.
Eddies and Turbulence
10.53. The heating of the earth's surface
by the sun causes updrafts. At higher al-
titudes the air spreads out and sinks again.
This rising and sinking circulation forms an
eddy. When eddies are caused by solar heating,
the circulations are called thermal turbulence.
A-50
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Basic Meteorology
10.54. When the wind blows over an object
such as a bush or a house, eddy circulations
are also set up in the lee of the obstruction.
These eddies are called mechanical turbulence.
10.55. When the sunlight hits the ground on
a clear day with light winds, the atmospheric
lapse rate is superadiabatic. Thermal turbu-
lence is created. If there is a smoke plume,
it will appear as a looping plume following
the eddy circulations.
10.56. A plume which blows close above a
building may also appear as a looping plume.
However, this time the looping will be caused
by the mechanical turbulence in the lee of
the obstruction.
10.57. The bringing of a plume downward in
the lee of a building by the mechanical turbu-
lence is called "downwash".
Suggested Additional Reading
Part B
Meteorologic Fundamentals.
Other
"Meteorology and Air Pollution", R. C.
Wanta, Air Pollution Vol. I, edited by
A. C. Stern, 1968.
"Air Pollution Climatology", R. A.
McCormick, Air Pollution Vol. I,
edited by A. C. Stern, 1968.
Weather. A Guide to Phenomena and Fore-
casts". P. E. Lehr, R. W. Burnett, and
H. Z. Zitn. Golden Press, New York, 1965.
A-51
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XI. METEOROLOGICAL FACTORS IN SMOKE READING
Effects on Reading of Plume Density
11.1. The stronger the wind, the more it
dilutes the plume and the less dense the
effluent appears.
11.2. If the wind is blowing a plume toward
an observer, he is looking through the length
of the plume. He will be looking through a
longer portion of the plume than if he were
looking through the width of the plume. Thus,
the plume will appear more dense.
11.3. An increase in the illumination of
a plume results in an increase in the contrast
between the plume and its background causing
the plume to look more dense. Cloudy skies
cut down on the illumination and thus the
contrast.
11.4. A smoke reader picks out a contrasting
background against which to view a plume. White
smoke read against a white cloud background or
black smoke read against a dark cloud background
reduces the contrast and makes the plume appear
less dense.
11.5. A plume disperses more rapidly in an
unstable atmosphere than in a stable atmosphere.
Downwind, a coning plume looks less dense than
a fanning plume. However, if an observer looks
at them both while they are near the stack,
their densities will be equal since they have
not begun to spread out.
11.6. When an observer looks at a plume
through a hazy atmosphere the contrast be-
tween the plume and its background is weakened.
The plume, under these conditions, does not
look as dense as it would on a clear day.
11.7. When an observer looks at a white
plume with the sun in front of him, the plume
scatters more light toward the observer than
is the case for an observer looking at the
plume with the sun at his back. This in-
creased scattering by the white plume it-
self results in a higher density reading
by the observer looking toward the sun. For
dark plumes on a clear day, the viewer looking
toward the sun also sees a plume that appears
to be more dense. On an overcast day, the two
viewers agree on the density of the plume.
Atmospheric Humidity and Water
Vapor Plumes
11.8. A plume containing large amounts of
water vapor will be visible for longer dis-
tances under conditions of high atmospheric
humidity. The moisture content of the air is
great enough so that water droplets in the
plume are prevented from evaporating. Thus
the water remains in the visible liquid phase
instead of changing into the invisible vapor
phase.
11.9. A "detached plume" occurs when a
moisture-laden effluent is emitted from a
stack at a temperature above the boiling
point of water. The plume becomes visible
only after the effluent has been cooled down
by the air to a temperature where the water
vapor condenses to the liquid droplet state.
If the atmosphere is hot, the cooling will
take some time. Then, there will be a space
between the top of the stack and the point
where the plume becomes visible.
11.10. Pure-water plumes or plumes con-
taining water and other material can be de-
termined in the following manner
(a) A pure-water plume disappears
rather quickly and is distin-
guished by its wispiness.
(b) If there is other material
mixed with the water, the
plume of this material will
remain after the water has
evaporated.
(c) Water plumes will be denser
and continue longer on cold
days or on moist days since
the atmospheric relative hu-
midity is higher then.
(d) A water plume will be detached
from the stack on hot days,
but not on cold days.
Useful Information That a Smoke
Inspector Can Obtain From the
Daily Weather Map
11.11. The passage of fronts or low-
pressure areas generally brings precipita-
tion and strong winds. The precipitation
will remove most of the particles from the
air and improve the visibility. The strong
winds will also clean out the air.
11.12. After a cold front passes the skies
will generally become cloudless. Radiation
inversions will form at nights causing fanning
plumes in the mornings. The colder weather
will produce denser and longer water plumes.
11.13. Near the center of the high-
pressure area the wind speeds will be low,
the air will be hazy, and visibility will
be poor. If the high remains stationary
A-52
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Meteorological Factors in Smoke Reading
for several days, smog will increase, especially
in the fall or summer.
11.14. The precipitation preceding a warm
front is mostly of a steady type. That accom-
panying or preceding a cold front is of a
showery type.
11.15. Wind direction is generally parallel
to the isobars, the lines of constant atmospheric
pressure. If one stands with his back to. the
wind, the lower pressure will be on his left
and the higher pressure will be on his right.
(In the Southern Hemisphere this relationship
is reversed.)
11.16. The weather along a stationary front
will be mostly rainy.
11.17. Upper level winds (5,000' to 30,000')
probably will not be in the same direction as
the surface winds shown on the map. Upper
level winds blowing over oceans, the Gulf of
Mexico, or the Great Lakes may bring cloudiness
inland. This will reduce the illumination and
change the background for plume reading.
Weather Observations to be
Made by the Smoke Reader
11.18. The Visible Emission Report Form has
several items of observations of sun and weather
which must be filled out to show the conditions
that existed while the plume reading was done.
These data are to insure that proper procedures
were being followed in the observation and they
may be needed if a case is brought to trial.
11.19. Cloud cover is the amount of sky
covered, but not necessarily hidden by clouds.
11.20. Cloud cover is usually measured in
tenths of the sky filled with clouds (at any
height).
11.21. Terminology:
(a) Clear - no clouds are present or
less than one-tenth of the sky
is covered.
(b) Scattered - one-tenth to five-
tenths of the sky is covered
by clouds.
(c) Broken - more than five-tenths
and less then nine-tenths of the
sky is covered by clouds.
(d) Overcast - more than nine-tenths of
the sky is covered by clouds.
11.22. Method of estimating cloud cover -
one may divide the sky dome into four quadrants
and estimate the number of tenths of coverage
in each quadrant. Then the average of these
four values can be used as the tenths of
coverage of the entire sky.
11.23. Wind direction is the direction
from which the wind is blowing. The direction
may be recorded from 16 or 8 points of the
compass. The observer must know his correct
orientation from a compass or a map so he can
determine which direction is north.
11.24. Anemometers are the instruments
used to measure the wind speed. They may be
of the cup type or the propeller type. They
are standardly placed in an open area at 33
feet (10 meters) above the ground.
11.25. In the absence of an anemometer
the Beaufort Scale of Wind-Speed Equivalents
may be used to estimate the wind speed at 10
meters.
11.26. Wind speed should generally be re-
corded in miles per hour.
11.27. The wind direction and speed may be
different at different heights above the sur-
face. The smoke inspector should try to
estimate the wind speed at the height of the
plume.
11.28. The variations of wind with height
are due to the surface friction, obstructions,
and differential heating of different surfaces.
The wind is slowest close to the ground be-
cause the effect of friction is greatest there.
11.29. Frequently, the wind speed and
direction will change during a plume obser-
vation so that a range of speeds and directions
must be entered on the report.
11.30. Atmospheric stability can also be
estimated by the observer if he notes such
things as the time of day, wind speed, and
plume shape.
11.31. The observer should distinguish
cases of downwash of plumes in the lee of
buildings or trees.
A-53
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Meteorological Factors in Smoke Reading
THE BEAUFORT SCALE OF WIND-SPEED EQUIVALENTS
General
Description
Calm
Light
Gentle
Moderate
Fresh
Strong
Gale
Whole gale
Hurricane
Specifications
Smoke rises vertically.
Direction of wind shown by smoke drift
but not by wind vanes.
Wind felt on face; leaves rustle;
ordinary vane moved by wind.
Leaves and small twigs in constant
motion; wind extends light flag.
Rasies dust and loose paper; small
branches are moved.
Small trees in leaf begin to sway; crested
wavelets form on inland waters.
Large branches in motion; whistling heard
in telegraph wires; umbrellas used with
difficulty.
Whole trees in motion; inconvenience
felt in walking against wind.
Breaks twigs off trees ; generally
impedes progress.
Slight structural damage occurs (chimney
pots and slate removed).
Trees uprooted; considerable structural
damage occurs .
Rarely experienced; accompanied by
widespread damage.
Limits of Velocity
33 feet (10 m)
above level ground
Miles Per Hour
Under 1
1 to 3
4 to 7
8 to 12
13 to 18
19 to 24
25 to 31
32 to 38
39 to 46
47 to 54
55 to 63
64 to 75
Above 75
Suggested Additional Reading
Part B
Effects of Meteorological Parameters on
Transport and Diffusion.
Pollutant Concentration Variation.
Other
"Atmospheric Dispersion of Stack Effluents",
G. H. Strom, Air Pollution Vol. _!, edited by
A. C. Stern, 1968.
Weather, A Guide to Phenomena and Forecasts,
P. E. Lehr, R. W. Burnett, and H. Z. Zim,
Golden Press, New York, 1965.
A-54
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XII. LEGAL ASPECTS OF VISIBLE EMISSIONS
History and Test Cases
12.1. Law may be divided into two categories-
common law and statute law.
12.2 Early air pollution laws fell under the
category of prohibiting smoke as a common nuisance
or a public nuisance. Under these common law
nuisance regulations it had to be proven in each
individual case that the smoke was injurious or
offensive to the senses. In the case of a public
nuisance, it had to be proven that a large number
of persons were affected.
12.3. In modern times, smoke and air pollution
came to be regarded as an absolute nuisance (a
nuisance per se) and a state could pass a statute
that declared the emission of dense black smoke
to be illegal. Injury did not have to be proven
in each case.
12.4. The state may grant to a city, county,
or other local government the power to pass
ordinances regulating air pollution. They can
also grant this power to the Federal Government.
The state can later cancel the powers which
they granted earlier.
12.5. This power to regulate air pollution
is given to the states by the Tenth . Amendment
of the Constitution which states: "The powers
not delegated to the United States by the
Constitution nor prohibited by it to the
States are reserved to the States respectively,
or to the people."
12.6. The only constitutional limitation to
how far the State's air pollution control law
can go is in the Fourteenth Amendment to the
Constitution: "...nor shall any State deprive
any person of life, liberty or property, without
due process of law; nor deny to any person
within its jurisdiction the protection of law."
Most of the air pollution cases that are
appealed test the constitutionality of the
control ordinance by means of the "due process"
clause or the "equal protection" clause.
12.7. Once black smoke had been declared
illegal, laws were needed to limit the emission
by setting maximum permissible pollution stand-
ards, or regulating the use and operation of
equipment and fuels.
12.8. Examples of maximum permissable emis-
sion standards are the Ringelmann Standard and
the Equivalent Opacity Standard.
12.9. In 1910 the Ringelmann Chart was first
recognized legally in the United States by its
inclusion in a smoke ordinance for Boston passed
by the Massachusetts Legislature.
12.10. The constitutionality of the Los
Angeles rule which provides standards for
reading of densities and opacities of visible
emission (Rule 50 or Section 24242 of the
Health and Safety Code) has been tested twice,
in 1951 and in 1955. In both of these cases
its constitutionality was upheld by the Los
Angeles Superior Court. In 1955 an appeal
of the Superior Court's decision to the United
States Supreme Court was dismissed by the
Supreme Court.
12.11. Section 24242 states: "A person shall
not discharge into the atmosphere from any
single source of emission whatsoever any air
contaminant for a period or periods aggregating
more than three minutes in any one hour which
is
"(a) As dark or darker in shade as
that designated as No. 2 on the
Ringelmann Chart as published
by the United States Bureau of
Mines, or
(b) Of such opacity as to obscure
an observer's view to a degree
equal to or greater than does
smoke described in subsection (a)
of this section."
12.12. The 1951 case, People Versus Inter-
national Steel Corporation, dealt with sub-
section (a) of Rule 50. The 1951 Supreme
Court dismissal directly concerned section
(b) and involved four separate cases of smog
(1) People Versus Plywood Manufacturers
of California
(2) People Versus Shell Oil Company
(3) People Versus Union Oil Company
(4) People Versus Southern California
Edison Company
Other cases approving the use of the Ringel-
mann Chart include: Board of Health of
Weehawken Township Versus New York Central
Railroad (New Jersey, 1950), and Penn-Dixie
Cement Corp. Versus City of Kingsport
(Tennessee, 1949).
12.13.
lished
(a)
(b)
The California appeal cases estab-
That the Code is constitutional
That it is permissible for a
statute to adopt for a descrip-
tion of a prohibited act a
publication of the United States
Bureau of Mines
A-55
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Legal Aspects of Visible Emissions
(c) That inspectors trained in the
use of the Ringelrnann Chart are
experts. They may testify as
expert witnesses concerning the
Ringelmann number of a particular
smoke emission without having had
a chart in their possession while
observing the plumes.
(d) That even though the ordinary
person is uncertain whether a
smoke plume is as dark as Ringel-
mann No. 2 or whether its opacity
equals that of smoke matching
Ringelmann No. 2 is no reason for
the unconstitutionality of the Rule.
(e) That the drawing of a line be-
tween permission and prohibition
(Ringelmann No. 2) is a matter
of legislative discretion which
will not be reversed by the Courts
unless abused.
(f) That if the plume, fairly viewed
from any position, exceeds the
regulation of Ringelmann shade, the
smoke is in violation no matter how
light the color may look to someone
situated at another vantage point.
Equivalent Opacity and
Smoke Emissions Laws
12.14. Some requirements for a good air
pollution law are:
(a) It must have the power to reduce
contamination.
(b) It must be enforceable. It must
be capable of being enforced
uniformly and it must not be
expensive to enforce.
(c) It must be reasonable.
(d) It must be clear and precise
so that people can under-
stand it and avoid breaking it.
(e) It is not necessary to prove
that the owner of the stack had
criminal intent in violating
the ordinance, just the fact
that his smoke is blacker than
Ringelmann No. 2 is sufficient.
(f) Any classification of sources it
established must be reasonable.
For example, an industry operates
its stack for profit while a home-
owner does not; therefore, different
emission standards can be required
of industrial and domestic chimneys.
12.15. As a practical matter, judges will
weigh the equities in a case to determine
which of the two parties will sustain the
most injury. They would not put a large
company out of business, but could require
them to pay a fine or install a control de-
vice.
12.16. Smoke emissions and equivalent
opacity regulations may restrict the shade
of smoke to be no darker than Ringelmann
No. 1, 2, or 3, depending upon the source
and the conditions.
12.17. The different sources regulated may
be ilisted as fuel burning equipment, inter-
nal combustion engines, open fires, incinera-
tors, railroad locomotives, and steamships.
The restricted sources may also be described
as stacks or vents or as any single source of
emissions whatsoever.
12.18. Different restrictions may apply to
incinerators and domestic installations.
12.19. Limitations may be set allowing
smoke of a darker shade for several minutes
of every hour during periods when a new fire
is being built.
12.20. Exceptions may be granted for
fires used in training firemen or for the
prevention of frost in orchards or on farms.
There may also be exceptions for industrial
accidents which cause black smoke or for
special processes.
12.21. Codes may exclude plumes of un-
combined water from the restrictions.
Local Regulations
12.22. The air pollution inspector must
know and understand the visible emissions
regulations which he will be enforcing.
How To Be An Expert Witness
(1) Under ordinary circumstances the
average citizen cannot testify
as to his opinions or conclusions,
but the expert witness can. The
opinion of the expert witness
helps the judge make his decision.
(2) It is preferable to subpoena a
witness, even a smoke inspector,
to appear in court rather than
to have him appear voluntarily.
When the witness is subpoenaed,
it demonstrates that he is not
A-56
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Legal Aspects of Visible Emissions
appearing in court just because he
has a prejudiced opinion for or
against one of the parties in the
case.
(3) Before appearing in court, pre-
pare your materials and refresh
your memory. An attorney spends
2 to 10 hours in preparation for
every hour in court. An expert
witness should spend a comparable
amount of time in reviewing his
observations before he testifies.
(4) As an expert witness the air
pollution officer should not
have to read his testimony.
However, he has a right to
refer to his records and notes
to refresh his memory.
(5) Since the case may not appear in
court until months after the vio-
lation occurred, the officer should
complete his report fully at the
time of violation.
(6) If you take a picture of a plume,
you should know what operation or
process is going on in the plant
at the time of the picture. Record
the time, weather, film type, ex-
posure setting, lens type, and
distance from the plume.
(7) Before having any telephone conver-
sations with a plant operator, meet
the man so that you can later iden-
tify his voice on the phone.
(8) Investigate every case thoroughly.
Do not become overconfident after
you have appeared in court several
times.
(9) Behavior on the witness stand:
(a) Dress and act like an expert.
(b) Be responsive to the question
that is asked you. Don't
volunteer information about
some related topic or question.
(c) Take a second to frame your
answer before giving it.
(d) If you hear "objection", quit
talking.
(e) If you make a mistake, admit it.
(f) If you cannot answer just "yes"
or "no" to a question, say so.
(g) Keep calm. Don't lose your temper.
(h) Don't try to second guess your
attorney.
(10) You will be directly examined
by your attorney and cross-
examined by the opposing attor-
ney. There can then be a re-
direct examination and a recross
examination. You can also be
recalled at a later time to
clear up your testimony.
Suggested Additional Reading
Part B
Approaches to Establishing Control
Regulations.
Legal Aspects of Air Pollution.
Other
"The Law of Air Pollution Control",
Air Pollution Control Field Opera-
tions Manual, edited by M. I.
Weisburd, PHS Publication No. 937,
1962.
A Compilation of Selected Air
Pollution Emission Control Reg-
ulations and Ordinances. DHEW,
PHS, Publication No. 999-AP-43,
1968.
A-57
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XIII. OBSERVATION REPORTS FOR VIOLATIONS
13.1. The purpose of making a visual obser-
vation of the degree of blackness or whiteness
of a plume is to collect evidence of the vio-
lation of a law or regulation.
13.2. To provide a sufficient basis for
court prosecution, the inspector must gather
evidence essential for a prima facie case --
that is, a case which unless contradicted adds
up to a violation of the law.
13.3. Each and all of the elements of the
violation must be proven or else there is no
case to take to court. For instance, if the
regulations states:
"A person, owner, agent, operator, firm
or corporation shall not discharge into
the atmosphere from any single source
of emission whatsoever any air contami-
nant 'for a period or periods aggregating
more than three minutes in any one hour
which is as dark or darker in shade
than that designated as No. 2 on the
Ringelmann Chart..."
Then all of the following must be proven:
(a) A person, owner, agent, operator, firm
or corporation
(b) Discharged
(c) Into the atmosphere
(d) From a single source
(e) A contaminant
(f) Of greater than No. 2 Ringelmann
(g) For more than 3 minutes in 1 hour.
13.4. The report and the citation forms when
filled out completely assure the inspector that
he has collected the data essential for support-
ing a prosecution of a violation.
13.5. The written report is not in itself
the evidence that is used to prove a case in
court. Rather, the evidence compiled by an
inspector consists of his expert opinion con-
cerning the shade of the emissions he observed
and his testimonial evidence given when he
testifies to the facts surrounding his observa-
tions.
13.6.- The written report may not actually
appear in the court proceedings, but the in-
spector may use it to refresh his memory.
13.7. The facts that the inspector should
record in his report of the observation include:
(a) The nature and extent of the
violation
(b) The time and location of
the violation
(c) The person(s) responsible
for the violation
(d) The equipment involved with
the violation
(e) The operational or maintenance
factors which caused the viola-
tion.
13.8. This information can be filed in two
reports - a smoke observation report and a
plant operation report. The latter would
cover information identifying and describing
the equipment which generated the plume and
determining the factor(s) which caused the
violation.
13.9. Either of the two reports might
contain information concerning the names
and addresses of the owners of the company
and of the operators of the equipment as
well as any remarks these people may have .
regarding the equipment.
13.10. The smoke observation portion of
the report form should include spaces for
the following supplementary information:
(a) Direction or distance of the
observer from the source
(b) Direction from which the wind
was blowing and, possibly,
the wind speed
(c) Weather conditions during the
observation describing whether
the sky was clear, overcast,
scattered, or broken and
whether it was hazy or raining
(d) Date and time during which the
observation was made
(e) Name and address of the firm
where the observation was made
(f) Type of air contaminant
(g) Description of the source, such
as number of stacks and their
height
(h) Signature of the inspector.
13.11. The basic portion of the smoke
observation report should record the visible
emissions observed, showing the continuous
time intervals for each density and opacity
and color changes. The inspector should note
to the nearest quarter minute the beginning
and ending observation times for each change
of density or color.
A-58
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Observation Reports for Violations
13.12. The total violation time for each
hour of observation should be recorded as well
as the total violation time during the entire
period of observation.
13.13. A photograph of the source can be
taken before or after, but not during, the
observation. Photographs do not always give
a true reproduction of plume color.
13.14. It is suggested that a violation
notice not be issued to the owner of the
equipment unless it is in violation for 1
minute longer than the legal limit and for
1/2 Ringelmann or 10 percent opacity greater
than the legal limit.
Special Designations
13.15. In some state, county, and municipal
visible emissions regulations, special source
categories or specific sources are named. Some
of these include
(a) Fuel-burning equipment
(b) Combustion equipment
(c) Apartment houses
(d) Office buildings
(e) Schools
(f) Hotels
(g) Hospitals
(h) Process equipment
(i) Motor vehicles
(j) Internal combustion engines
(k) Diesel motor vehicles
(1) Railroads
(m) Steamships
(n) Incinerators
(o) Open fires
13.16. Emissions from incinerators are often
required not to exceed a Ringelmann No. 1 or
an equivalent opacity of 20 percent although
the limit for other sources is No. 2 Ringelmann.
13.17. Some ordinances and regulations grant
exceptions to the visible emissions regulations.
A few of these are
(a) Smoke may attain densities as high
as No. 3 for an aggregate of 3
minutes in any 15 consecutive
minutes when a new fire is being
built, a fire box is being cleaned,
tubes are being blown, or an equip-
ment breakdown occurs. (Regulations
may vary on the time allowed.
Other codes include 3 minutes
in a 30-minute period, 12
minutes in a 24-hour period,
etc.)
(b) Smoke from railroad locomotives
or steamships may attain values
as high as No. 3 Ringelmann for
a limited number of minutes
during periods ranging from 6
minutes to 8 hours.
(c) In some localities, exceptions
to visible emission regulations
may be granted to certain in-
dustrial operations. Some
examples from one state's code
are
(1) Transfer of molten metals
(2) Emissions from transfer
ladles
(3) Coke ovens when pushing
coke after discharge from
the ovens
(4) Water quenching of coke
after discharge from the
ovens
(5) Gray iron cupola furnaces.
Suggested Additional Reading
"Air Pollution Control Field
Operations", Air Pollution Con-
trol Field Operations Manual.
edited by M. I. Weisburd, PHS
Publication No. 937, 1962.
"Collecting and Reporting Evidence
of Violations", Air Pollution Con-
trol Field Operations Manual, edited
by M. I. Weisburd, PHS Publication
No. 937, 1962.
A-59
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XIV. EMISSION GENERATOR
14.1. For use in training personnel to read
smoke, it is necessary to have a device which
will produce both black smoke and white smoke
plus an instrument to measure the opaqueness of
the'smoke that is produced.
14.2. Smoke-generating devices have been
built by some air-pollution control agencies
for their use. The principles of operation
of all these units are similar. Other agencies
have purchased manufactured generators.
unit. Considerable heat is required for
vaporizing the fuel oil. Sufficient heat
is provided by operating the generator under
an appreciable load.
14.8. In the production of both black
and white smoke, the smoke is diluted with
ambient air before it enters the stack. The
degree of dilution is controlled by dampers
in the air inlet to the induced draft blower
fan.
Mark II Smoke Generator
14.3. The Mark II Smoke Observers Training
Unit, manufactured by Environmental Specialties
is the most widely used smoke generating unit.
It is portable and each unit is custom made;
however, the principal features of the Mark II
are present in all models.
Black Smoke
14.4. When a carbon-containing fuel is burned
with insufficient air, a smoky flue gas is pro-
duced. The smoke consists of partially burned
carbon particulates suspended in the gas.
14.5. In the smoke generator black smoke is
created by burning benzene or benzol with a
deficiency of oxygen. (Diesel fuel is used
by some generator operators.) This fuel is
burned in a furnace which consists of a 12-
cubic-foot steel combustion chamber lined with
refractory bricks. The combustion air entering
this chamber is limited. The benzene flow
into the furnace is controlled by a fine meter-
ing valve. The density of the black smoke is
varied by using this valve to adjust the rate
of fuel injection through a nozzle into the
combustion chamber.
White Smoke
14.6. To produce the white smoke, No. 2
fuel oil (the grade usually used for home or
commercial heating) is vaporized in the absence
of oxygen. This vapor is then condensed into
an aerosol cloud which has a white color. The
opacity of this cloud is controlled by adjusting
the flow of the No. 2 fuel oil.
14.7. In the Mark II the white aerosol vapor
is created by injecting the fuel oil through a
hypodermic needle into the manifold which carries
the hot exhaust from a small lawnmower-sized
gasoline engine. This engine runs a generator
which can provide electric power for the Mark II
Transmissometer
14.9. The opaqueness of the white or black
smoke is measured by transmissometer which is
located in a 4-foot length of pipe mounted
perpendicular to the smoke stack at a point
6 feet below the top of the stack. The
opaqueness measurement from the transmisso-
meter can be read by the generator operator
on a scale divided into Ringelmann numbers
and equivalent opacity percentages. The
transmissometer reading serves as the standard
with which the smoke reader compares his
visual observations.
14.10. The transmissometer for the Mark
II is a simple light source and photocell
combination. The light source may be a
flashlight bulb or automobile taillight
bulb mounted in a silvered reflector which
concentrates the light into a beam that
is aimed at the photocell 4 feet away.
14.11. One foot of the path length of the
beam is through the stack of the generator.
In this portion of the path the intensity
of the light is reduced in proportion to the
amount of smoke being produced by the genera-
tor. This smoke is prevented from entering
the remaining 3 feet of the transmissometer
path by circular smoke stops which reduce the
diameter of the transmissometer pipe. In
addition, these 3 feet of the transmissometer
path are continually flushed with outside air
by two fans, one mounted at each end of the
pipe.
14.12. The combination of smoke stops and
ambient air flushing insures that there will
be no smoke buildup in the pipe. As a result,
the only obstruction to the light beam occurs
when the beam passes through the 1-foot-
diameter stack.
14.13. The percent transmission of light
that reaches the photocell is relayed electri-
cally to the operator's station. Here, it
may be read from the dial of a micro-
ammeter or from a pen trace on a recorder
depending upon which of these devices is
A-60
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Emission Generator
supplied with the generator unit.
12.14. The transmissometer system is cali-
brated from 100 percent to zero transmission
(zero to #5 Ringelmann and zero to 100 per-
cent equivalent opacity) by inserting several
grades of neutral density filters into the
light path between the bulb and the photocell
and adjusting the microammeter or recorder for
the percent of light transmitted.
Conduct of the School
12.15. The smoke reader's training on the
smoke generator begins with a familiarization
series of black and white smoke densities.
Upon the sound of the horn, the instructor calls
out the meter or recorder reading of Ringelmann
number or equivalent opacity.
12.16. After this familiarization period the
students go through a practice run of 25 shades
of black and 25 shades of white smoke. Each
reading is made by the student at the sound of
the horn and entered on his training form just
as he will do it later when he is reading for
qualification.
12.17. Following the practice run the stu-
dents will begin their qualification runs of
25 white and 25 black shades.
12.18. In between qualification runs the
generator operator may conduct short series
of familizarization review runs for the
benefit of the students.
Other Smoke Generating Equipment
12.19. Los Angeles - 1962
(a) Black Smoke System
The oil burner is a modified mech-
anical pressure atomizing type. The
combustion chamber is a 40-cubic-
foot-rectangular steel box lined with
6 inches of refractory fire clay.
The various degrees of incomplete com-
bustion of the fuel are obtained by
adjusting the fuel flow. The smoke
from the combustion chamber passes
along a horizontal duct into a cooling
chamber and then into the stack. A
forced-draft fan discharges ambient
dilution air into the base of the
stack and pushes the smoke up the
stack. This forced draft helps to
prevent distortion of the plume by
the wind as the smoke exits from
the stack. The cooling chamber
prevents secondary combustion
from occurring at the base of
the stack as the combustion
products are diluted with air.
(b) White Smoke System
The "white smoke" is created
by spraying a distillate type
of oil into a chamber where it
is vaporized by the heat gene-
rated in an adjacent heating
chamber. The vapor is forced up
the stack by a forced draft fan
which pumps in dilution air.
The vapor is condensed into a
white cloud of aerosols. The
operator controls the opacity
of the plume by adjusting the
rate at which the oil is sprayed
into the vaporizing chamber and
the temperature of the heating
chamber. The heat in this
chamber is created by burning
distillate oil.
(c) Opacity and Density Detection
System
Similar to the Mark II, this
system consists of a light source
and a photoelectric cell posi-
tioned at opposite ends of a light
tube protruding horizontally from
each side of the smoke stack. The
milliammeter which registers the
light received by the photocell
has a scale arranged so that 100
indicates no light and zero indi-
cates free passage of light.
When the operator adjusts the
output of the light source to
cause a full-scale deflection of
the milliammeter, an opacity of
zero is read. If the light is
turned out, no light energy
reaches the cell and the milli-
ammeter reads 100 percent opacity.
Suggested Additional Reading
Part B
Reading Visible Emissions.
Other
"Reading Visible Emissions". Air
Pollution Control Field Operations
Manual, edited by M. I. Weisburd,
PHS Publication No. 937, 1962.
A-61
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PART B - SUPPLEMENTAL READINGS
37
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CLASSIFICATION OF SOURCES OF EMISSION
C. A. Lindstrom
I MAJOR CLASSES OF SOURCES OF
EMISSION
For convenience, air pollution sources are
divided into two classes: (1) point-sources
and (2) area-sources.
A Point-Sources
Point-sources are largely industrial
in nature, thus permitting their potential
to pollute a community atmosphere to be
readily assayed on an industry-by-indus-
try (source-by-source) basis. They are
fixed^and commonly occupy a limited
area 'relative to the community.
B Area-Sources
Area-sources are those which cannot
be assayed practicably on a source-by-
source basis. They are either fixed or
mobile, and commonly scattered through-
out the community.
H CLASSIFICATION OF AREA
SOURCES
Area-sources may be classified as fol-
lows:
A Combustion of Fuels
1 Combustion of fuels in stationary
sources
a Fuel for power production
1) Public utility plants
2) Industrial power plants
b Fuel for personal comfort and
convenience
1) Private homes
2) Service industries:
a) Lodging (e.g. hotels, motels)
b) Medical (e. g. hospitals, clinics)
c) Educational
d) Governmental
e) Repair services
f) Laundry and cleaning
g) Entertainment
h) Commercial (e. g. stores,
offices, warehouses)
i) Others
2 Combustion of fuels for transportation
a Motor vehicles
b Railroads
c Ships
d Aircraft
B Incineration of Solid Wastes
1 Private homes
2 Municipal
3 Industrial
4 Commercial
C Evaporation of Petroleum Products
1 Solvent usage
a Surface coating
b Degreasing
c Dry cleaning
d Plastics manufacture
e Rubber manufacture
2 Storage and marketing
a Tank farms
b Service stations
EAQM II 8. 66
B-l
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Classification of Sources of Emission
D Odor Producting Activities
1 Animal odors
a Meat packing and rendering plants
b Fish-oil odors from manufacturing
plants
c Poultry ranches and processing
2 Odors from combustion processes
a Gasoline and diesel engine exhaust
b Coke-oven and coal-gas odors
(steel mills)
c Maladjusted heating systems
3 General industrial odors
a Burning rubber from smelting and
debonding
b Odors from dry-cleaning shops
c Fertilizer plants
d Asphalt odors (roofing and street
paving)
e Asphalt odors (manufacturing)
f Plastic manufacturing
4 Odors from combustible waste
a Home incinerators and backyard
trash fires
b City incinerators burning garbage
c Open-dump fires
5 Refinery odors
a Mercaptans
b Crude oil and gasoline odors
c Sulfur
6 Sewage odors
a City sewers carrying industrial
waste
b Sewage treatment plants
III CLASSIFICATION OF POINT-SOURCES
Industrial plants represent a complex chemi-
cal system which are most effectively treat-
ed on an individual basis. Each industry
presents a unique air pollution problem
since the polluted effluents are a result of
the peculiarities of the manufacturing opera-
tion (e. g. the raw materials, the fuels, the
process method, the efficiency of the process
method, and air pollution control measures).
Industries fall into standard categories, for
each of which, the air pollution potential
may be computed. Metropolitan economics
with a heavy concentration of industrial
activity within a special category exhibit
the types of air pollution problem associated
with that category; those with a diversified
economy have a varied type of air pollution
problem. The diversity of types of industry
in-a community may be estimated from a
study of employment figures, careful con-
sideration being given to highly automated
activities when analyzing the data.
Standard industrial categories, together
with a brief description of the nature of
activity and the associated types of pollution
problem are shown in Table 1.
REFERENCE
1. Air Pollution Control Field Operations
Manual, Public Health Service
Publication No. 937, Superintendent
of Documents, U. S. Government
Printing Office, Washington, D. C.
1962.
B-2
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TABLE 1
STANDARD INDUSTRIAL CATEGORIES
MANUFACTURING
INDUSTRY
NATURE OF ACTIVITY
TYPES OF AIR POLLUTION
PROBLEM
PRIMARY METALS
(Ferrous and non-
ferrous)
Primarily fuming of metallic oxides,
and emission of CO, smoke, dust and
Primary smelting of ore to obtain metallic elements.
Steel Mills--manufacture of steel alloy products by
removal of graphitic carbon from iron and addition of ash from melting operation, depending
alloy elements. Ferrous and nonfefrous foundries-- on the volatility and impurities of the
cast products from sand or permanent molds. metals, scrap or ore concentration.
Smelting is most notorious, emitting
Secondary smelting--separates ingots of each element sulfur dioxide, lead and arsenical copper
from scrap. Secondary ingot production-prepares fume, depending on metal smelted.
alloyed ingots from scrap.
FABRICATED
METAL PRODUCTS
MACHINERY
Manufacture of a large variety of products: Heating Metals melted are usually refined, and
and plumbing equipment, tools and hardware, structur-melting operations are easily controlled.
al metal products, cutlery, metal stamping and coat-
ing, lighting fixtures, tin cans and others. Usually
involves metal melting from ingot; machine shops,
metal finishing and surface coating.
Machining and finishing of component machinery
parts and/or their assembly in the production
of a wide variety of mechanical equipment (but not
including electrical machinery). Farm implements,
machine tools, printing, office and store equipment,
oil field production and refinery equipment, textile,
shoes and clothing equipment, construction equipment,
household equipment, etc.
Principal air contaminants are metallic
fumes and dusts from foundries and
solvent mists and vapors from application
of protective coatrigs in finishing de-
partments.
Primarily dusts and mists from finish-
ing departments, some smoke and
fumes from quenching in tempering and
heat treating. Metal melting is not
usually involved.
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TABLE 1 (Cont'd)
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MANUFACTURING
INDUSTRY
NATURE OF ACTIVITY
TYPES OF AIR POLLUTION
PROBLEM
ELECTRICAL
MACHINERY
MINING
Manufacturing and assembly of machinery; appa-
ratus and supplies for the generation, storage,
transmission, and utilization of electrical energy,
principally electrical motors and generators.
Air contaminants similar to those de-
scribed under machinery.
Quarrying and milling of solid products and minerals-- Waste explosive gases, CO, etc.,
coal, iron and metallic ore. dusts and fumes.
Petroleum and petroleum refining. Drilling and ex-
traction of crude petroleum from oil fields, recovery
of oil from oil sands and oil shale, and production of
natural gasoline and cycle condensate. Oil refining
consists of a number of complex flow processes based
on heat and pressure which crack, build up, alter or
segregate hydrocarbons from crude oil in the produc-
tion of a large variety of commercial products from
high octane gasolines to heavy oils and greases.
Natural gas originates from the oil fields in the south-
west.
FURNITURE, Logging and milling, including veneering, planing,
LUMBER AND WOOD and plywood manufacturing; boxing and container
PRODUCTS manufacturing; sawdust and other by-product manufac-
turing. Furniture mfg., household, office and store
fixtures. Involves production wood working, (planing,
milling, cutting, sanding, shaping, etc.), finishing
(staining, priming, oainting, etc.) and occasionally
elimination of large volume production wastes by
burning.
Due to the large number of production
steps, all forms of air pollution arise
from refineries. These include vapors
from evaporation of petroleum products
in handling and storage; sulfur dioxide
and smoke plumes from scavenging
and burning of refinery fuels in heating
equipment; odors, mists and dusts
from cracking operations.
Fines and dusts from milling operations.
Paint and solvent emissions from sur-
face coating. Smoke from burning
waste lumber, mill ends, fines and
sawdust.
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TABLE 1 (Cont'd)
MANUFACTURING
INDUSTRY
NATURE OF ACTIVITY
TYPES OF AIR POLLUTION
PROBLEM
TRANSPORTATION
EQUIPMENT
CHEMICALS AND
ALLIED PRODUCTS
MINERALS
(Stone, Clay and
Glass Products)
Manufacture and/or assembly of component parts
for ships, automobiles, rolling stock, air-
craft and other transportation equipment involving
fabrication of structural assemblies and components,
and, in the case of ships and rolling stock, riveting,
welding and sheet metal work, A high degree of
specialization, especially in automobiles and aircraft,
necessitates extensive subcontracting activities,
or concentration of many captive industries into
coordinated production systems.
Manufacture of almost an unlimited variety of
products: petro-chemicals, heavy or industrial
chemicals such as sulfuric acid, soda ash, caustic
soda, chlorine and ammonia; Pharmaceuticals,
pesticides, products of nuclear fission, plastics,
cosmetics, soaps, synthetic fibers, such as nylon,
pigments, etc. Manufacturing techniques encompass
virtually the entire chemical technology.
Aside from assembly lines which are
not in themselves significant sources
of air pollution, captive subsidiary
operations may involve foundries,
heat treating, wood-working, plating,
anodizing, chem-milling and surface
coating operations which contribute all
types of air contaminants including
organic vapor emissions from the
application, drying and baking of pro-
tective coatings.
Chemical technology makes possible
all forms of pollution, involving the
emissions of the chemicals (both chemi-
cal and end-product) and the derivative
or reaction products of the chemicals
in process or in the atmosphere.
Manufacture from earth materials (stone, clay and
sand), glass, cement, clay products, pottery,
concrete and gypsum products, cut stone products,
abrasive and asbestos products, roofing materials,
bricks, etc. , involving mechanical processes such
as crushing, mixing, classifying and grading; batching,
drying and baking in kilns to vitrify dishware, and
melting and forming to produce glass products.
Dusts from mechanical processes,
smoke and fumes from melting or
kiln operations.
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TABLE 1 (Cont'd)
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MANUFACTURING
INDUSTRY
NATURE OF ACTIVITY
TYPES OF AIR POLLUTION
PROBLEM
TEXTILE Includes milling and manufacturing of yarns, threads,
braids, twines, fabrics, rugs, apparel, lace, and a
vast variety of products involving processes of
spinning, spooling, winding, weaving, braiding,
knitting, sewing, bleaching, dyeing, printing,
impregnating, batting, padding, etc.
RUBBER Manufacture from natural, synthetic, or reclaimed
PRODUCTS rubber (gutta percha, balata, or gutta siak), rubber
products such as tires, rubber footwear, mechanical
rubber goods, heels and soles, flooring, and other
rubber products. Processes involve mastication,
mixing or blending of crude rubber, reclaim or
chemical rubbers, calendering, tubing, binding and
cementing, curing, etc.
PAPER AND ALLIED Manufacture of paper and paper products from wood
PRODUCTS pulp, cellulose fibers, and rags involving cutting,
crushing, mixing, cooking, and paper mills.
Lint and fines are emitted from produc-
tion wastes; organic vapor emissions
or other mists from dyeing, bleaching,
impregnating, cleaning; smoke from
combustion equipment required to power
weaves, looms, and other processing
and conveyor equipment.
Local dusts and carbon black emissions
from mixing and rolling operations, but
usually under careful control. Organic
vapor emissions from solvents used in
bonding and cementing, coating and
drying of products.
Some possible sawdust emissions,
but otherwise practically no emissions,
except from combustion equipment to
provide steam heat and power for
mechanical equipment. Construction
materials such as roofing paper involve
saturating paper with asphalt and
impregnating with minerals, causing
mist and dust problems.
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TABLE 1 (Cont'd)
MANUFACTURING
INDUSTRY
NATURE OF ACTIVITY
TYPES OF AIR POLLUTION
PROBLEM
PRINTING AND
PUBLISHING
Printing and publishing by means of letter-
press, lithography, gravure, or screen, book-
binding, typesetting, engraving, photo-engraving,
and electrotyping. Involves lead melting pots for
typesetting machines, and significant quantities of
inks containing organic solvents.
Lead oxide emissions are possible
from lead pots, but these are easily
controlled. Organic solvent emissions
arise from the large volume of inks,
particularly in rotogravure processes.
INSTRUMENTS
Manufacture and assembly of mechanical, electrical
and chemical instruments for dental, laboratory,
research and photographic uses, including watches
and clocks. Involves casting and machining of a
variety of hard metal alloys, including brass and
steel; assembly, plating and finishing.
Emissions from these plants are usually
controlled, but can involve smokes,
dusts, and fumes similar to those of
fabricating and machinery manufacturing
industries. Hard-chrome electrolytic
plating is usually involved with high
quality instrumentation, causing emission
of acid mists.
FOOD
AND KINDRED
PRODUCTS
OTHER
MANUFACTURING
INDUSTRIES
00
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Includes the slaughtering of animals and the curing
and smoking of meat products as well as the pre-
paration of all other foods such as dairy products,
canning and preserving of fruits, vegetables and sea-
foods; grain and feed milling, baking preparation of
beverages, including coffee, beer and other alcohols;
animal rendering, manufacture of fats, oil, grease,
tallow, etc.
Tobacco, ordnance and armaments, leather and
leather products, building construction, jewelry
and silverware, etc.
Most notably odors, particularly from
rendering operations and from poor
housekeeping where products are per-
mitted to decompose. Odors may also
occur from the handling of by-products,
and from coffee roasting. Dust from
grain and feed mill operations.
All types of air pollution arising from
basic processes described in the fore-
going.
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BASIC COMBUSTION CONCEPTS
Darryl J. von Lehmden*
I INTRODUCTION
Combustion is a chemical reaction. Complete
combustion consists of the rapid oxidation of
a combustible substance to innocuous carbon
dioxide and water accompanied by the release
of energy (heat and light).
II PRINCIPLES OF COMBUSTION
To achieve complete combustion, i. e., the
combination of the combustible elements
with all the oxygen which they can utilize,
sufficient space, time, turbulence, and a
temperature high enough to ignite the con-
stituents must be provided.
The "three T's" of combustion -- time,
temperature, turbulence -- govern the speed
and completeness of the combustion reaction.
For complete combustion, the oxygen must
come into intimate contact with the combus-
tible molecule at sufficient temperature, and
for a sufficient length of time, in order that
the reaction be completed. Incomplete
reactions may result in the generation of
aldehydes, organic acids, carbon and carbon
monoxide.
The factors influencing completeness of com-
bustion are evaluated in more detail below:
A Temperature
Every combustible substance has a mini-
mum ignition temperature, which must
be attained or exceeded, in the presence
of oxygen, if combustion is to ensue under
the given conditions. This ignition tem-
perature may be defined as the temperature
at which more heat is generated by the re-
action than is lost to the surroundings.
The ignition temperature for flame com-
bustion of combustible substances cover
a large range, as indicated in Table 1.' '
The ignition temperatures of the gases
volatilized from coal vary considerably
and are appreciably higher than the ignition
temperatures of the fixed carbon in the
coal. The gaseous constituents in the
coal are usually distilled off, but not
ignited, before the ignition temperature
of the fixed carbon is attained. Therefore
if complete combustion of the gases is to
be achieved it is necessary that the tem-
perature of the effluent gases be raised
to the ignition temperature of the gases.
The same principle applies to the complete
combustion of any mixture of combustible
substances. A sufficiently high tempera-
ture must be achieved which will burn all
the combustible compounds. To achieve
such a temperature it may be necessary
to add auxilliary heat to the combustible-
laden gas stream (e. g., via a gas fired
burner).
Since the reaction rate increases with
temperature, temperatures considerably
above the ignition temperatures of the
combustible may be necessary to accom-
plish complete combustion in a reasonable
amount of time.
B Oxygen
Oxygen is necessary for combustion to
occur. The end products of combustion
depend on the supply of oxygen. When
methane, for instance, is burned with
too little oxygen, solid carbon results
thus:
CH4 + O2 = C + 2H2O + Q (heat-of reaction)
The solid carbon agglomerates forming
particles of soot and smoke. If enough
oxygen is supplied, the carbon is burned
to carbon dioxide, thus:
Q
*Chemical Engineer, Air Pollution Training,
Training Program, SEC
PA. C.ce.3. 1.66
B-9
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Basic Combustion Concepts
Table 1. FLAME IGNITION TEMPERATURE IN AIR*
(At Pressure of One Atmosphere)
Combustible
Sulfur
Charcoal
Fixed carbon
Formula
S
C
C
Temper ature,°F
470
650
765
(bituminous coal)
Fixed carbon
(semibituminous coal)
870
Fixed carbon
(anthracite)
Acetylene
Ethane
Ethylene
Hydrogen
Methane
Carbon monoxide
Kerosene
Gasoline
C
C2H2
C2H6
C2H4
H2
CH4
CO
-
-
840
580
880
900
1065
1170
1130
490
500
- 1115
- 825
- 1165
- 1020
- 1095
- 1380
- 1215
- 560
- 800
* Rounded-out values and ranges from various sources;
a guide only.
Here, then it is completely burned, no
solid is set free, and hence there is no
smoke.
When carbon is burned with an insufficient
supply of oxygen, carbon monoxide
results:
2C +
= 2CO + Q
If enough oxygen is available, then carbon
dioxide results:
C + 02 = C02 -t- Q
The chemical reactions which occur during
the combustion of many compounds are
shown in Table 2. W
To achieve complete combustion of a com-
bustible compound with air, a Stoichiometric
(theoretical) quantity of oxygen must be
available. The quantity of air which must
be furnished to obtain theoretical com-
plete combustion for many combustible
compounds is shown in Table 3.
(1)
It is necessary, however, to use more
than the theoretical air required to assure
sufficient oxygen for complete combustion.
Excess air would not be required if it
were possible to have every oxygen
molecule combine with the combustibles.
The amount of excess air added to insure
complete combustion must be held at a
practical minimum to reduce the stark
heat losses. Realistic values of excess
air necessary to burn various fuel are
given in Table 4. '
C Time
A fundamental factor in the design and
performance of combustion equipment
B-10
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Basic Combustion Concepts
Table 2. COMMON CHEMICAL REACTIONS OF COMBUSTION
Combustible
Sulfur (to SOJ
A
Sulfur (to SO3)
Reaction
Carbon (to CO) 2C +
Carbon (to COJ
Carbon monoxide 2CO +
Hydrogen 2H,
= 2CO + Q
C + O2 = . C02 + Q
= 2C02 + Q
2
S
28
Methane CH. +
Acetylene 2C~KZ +
Ethylene C2H4 +
Ethane 2C2H6 +
Hydrogen sulfide 2H2S +
where Q = the heat of reaction
2H20
2SO
On
300
502 = 4C02
302 = 2C02
70 = 4C0
Q
Q
Q
Q
2H20 + Q
2H20 + Q
6H0+ Q
2SO0 + 2H.O + Q
£i &
is the time required for combustion of a
particle in relation to the residence time
in the equipment at combustion conditions.
The residence time (at conditions con-
ducive for complete combustion) should
be greater than the time required for
combustion of the particle.
The time of residence depends primarily
on aerodynamic factors including size
which are arbitrarly set in the design of
the unit. The time of combustion is con-
trolled by the temperatures and aero-
dynamic factors. The time of residence,
then, becomes a question of economy;
namely size versus temperature. The
smaller the unit, the higher the tempera-
ture must be to oxidize the material in
the time of contact.
D Turbulence
Not only must the oxygen be supplied,
but it must be intimately mixed with the
material being burned so that it is
available to the combustion substance at
all times. When burning solids, without
turbulence, the initial products of com-
bustion act as a screen for the incoming
oxygen and thereby slow down the rate of
surface reaction. The burning of gases
requires a thorough mixing of them with
air: otherwise separate zones between
the gases and air will form and they will
escape unchanged or incompletely burned.
Through the proper regulation and control
of these four factors, complete combustion
can be attained.
B-ll
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Table 3. COMBUSTION CONSTANTS
No. Substance
1 Carbon*
2 Hydro ten
3 Oxygen
4 Nitrogen (aim)
5 Carbon monoxide
6 Carbon dioxide
Paraffin scries
7 Methane
8 Ethane
9 Propane
10 n- Butane
1 1 Isobutane
12 n-Pentane
13 Isopemane
14 Neopcntane
15 n- He sane
Olefin series
16 Eihylene
17 Propylcnc
18 n-Butcne
19 Isobuienc
20 n-Peniene
Aromatic series
21 Benzene
22 Toluene
23 Xylenc
Miscellaneous gases
24 Acetylene
25 Naphthalene
26 Mett.)l alcohol
27 Hihyl alcohol
28 Ammonia
29 Sulfur*
31 Sulfur diotide
3"* Wjtcr *'anor
33 Air
Formula
C
H,
O,
Ni
CO
CO,
CH.
C,H,
C,H.
C.H,,
C.Hi.
C,H,,
C,H,,
C.H,!
C.H,,
C;H«
C,Ht
C.H.
C.H.
C.H..
C.H.
C:H.
C.H,,
C,H,
C,,H.
CH.OH
C.H.OI1
Nil,
5
H-S
SO-
Molecu-
lar Lb per
Weisht Cu Fl
12.01
2.016 0.0053
32.000 0.0846
28.016 0.0744
28.01 0.0740
44.01 0.1170
16.041 0.0424
30.067 0.01103
44.092 0.1196
58.118 0.1582
58.118 0.1582
72.144 0.1904
72.144 0.1904
72.144 0.1904
86.169 0.2274
28.051 0.0746
42.077 O.I 110
56.102 0.1480
56.102 0.1480
70.128 0.1852
78.107 0.2060
92.132 0.2431
106.158 0.2803
26.0)6 0.0697
128.162 0.3384
32.041 0.0846
46.067 0.1216
17.031 0.0456
31 06
34.076 0.0911
64.06 0.1733
1K.OI6 0.0476
2S.9 0.0766
CuFt
per Lb
187.723
11.819
13.443
13.506
8.548
23.565
12.455
8.365
6.321
6.321
5.252
5.252
5.252
4.398
13.412
9.007
6.756
6.756
5.400
4.852
4.113
3.567
14.344
2.955
11.820
8.221
21.914
10.979
5.770
21.017
13.063
SpGr
Air
1.0000
0.0696
1.1053
0.9718
0.9672
1.5282
0.5543
1.0488
1.5617
2.0665
J.0665
2.4872
2.4872
2.4872
2.9704
0.9740
1.4504
1.9336
1.9336
2.4190
2.6920
3.1760
3.6618
0.9107
4.4208
1.1052
1.5890
0.5961
I.IR98
2.2640
0.6215
1.0000
Heat ofC
Btu per Cu Ft
Gross Net
(Hijh) (Low)
325 275
Combustion
Btu per Lb
Gross Net
(Hijh) (Low)
14.093 14,093
61.100 51.62}
322 322
1013 913
1792 1641
2590 2383
3370 3113
3363 3105
4016 3709
4008 3716
3993 3693
4762 4412
1614 1513
2336 2186
3084 2885
3068 2869
3836 3S8«
3751 3601
4484 4284
5230 4980
1499 1448
5854 5654
868 768
1600 1451
441 365
647 596
4,347 4.347
23,879 21.520
22.320 20.432
21,661 19,944
21.308 19.680
21,257 19,629
21.091 19.517
21,052 19,478
20,970 19,396
20,940 19,40}
21,644 20.295
21,041 19.691
20,840 19,496
20.7}0 I9,}82
20.712 19,363
18.210 17,480
18,440 17,620
18,650 17,760
21,500 20.776
17.298 16,708
10.259 9.078
13.161 11,929
9.668 8,001
3.983 3.98}
7.100 6.545
For 100% Total Mr
Moles per mole of Combustible
or
Cu Ft per Cu Ft of Combustible
Required for Combustion Flue Products
O, N, Air CO, Hf> N,
1.0 3.76 4.76 1.0 ... 3.76
0.5 1.88 2.38 ... 1.0 1.88
0.5 1.88 2.38 1.0 ... 1.88
2.0 7.53 9.53 1.0 2.0 7.53
3.5 13.18 16.63 2.0 3.0 13.18
5.0 18.82 23.82 3.0 4.0 18.82
6.5 24.47 30.97 4.0 5.0 24.47
6.5 24.47 30.97 4.0 5.0 24.47
8.0 30.11 38.11 5.0 6.0 30.11
8.0 30.11 38.11 5.0 6.0 30.11
8.0 30.11 38.11 5.0 6.0 30.11
9.5 35.76 45.26 6.0 7.0 35.76
3.0 11.29 14.29 2.0 2.0 11.29
4.5 16.94 21.44 3.0 3.0 16.94
6.0 22.59 28.59 4.0 4.0 22.59
6.0 22.59 28.59 4.0 4.0 22.59
7.5 28.23 J5.73 5.0 5.0 28.23
7.5 28.23 35.73 6.0 3.0 28.23
9.0 33.88 42.88 7.0 4.0 33.18
10.5 39.52 50.02 8.0 5.0 39.52
2.5 9.41 11.91 2.0 1.0 9.41
12.0 45.17 57.17 10.0 4.0 45.17
I.S 3.65 7.15 1.0 2.0 5.65
3.0 11.29 14.29 2.0 3.0 11.29
0.75 2.82 3.57 ... 1.5 3.3J
SO,
1.0 3.76 4.76 1.0 ... 3.76
1.5 5.65 7.15 1.0 1.0 5.65
For
IOJK. Total Air
Lb per Use? Combustible
Required for Combustion Flue Products
0,
2.66
7.94
N,
8.86
26.41
Air CO,
11.53 3.66
34 J4
H.O N,
8.86
8.94 26.41
0.57
399
3.73
3.63
3.38
3.5S
3.55
3.55
3.55
3.53
3.42
3.42
3.42
3.42
1.42
3.07
3.13
3.17
3.07
3.00
1.50
2.08
1.41
1.00
1.41
1.90
13.28
12.39
12.07
11.91
11.91
11.81
11.81
11.81
11.74
11.39
11.39
11.39
11.39
11.39
10.22
10.40
10.53
10.22
9.97
4.91
6.93
4.69
3.29
4.69
2.47 1.57
17.27 2.74
16.12 2.93
15.70 2.99
I5-4S 3.03
15.41 3.03
15J5 3.05
I5J5 3.03
1SJS 3.05
15.27 3.06
14JI 3.14
I4JI 3.14
14.11 3.14
I4JI 3.14
Ujn 3.14
1X3* 3.38
13.51 3.34
13.JI 3.32
13.3* 3.31
12.** 3.4)
6.41 1.37
9.02 1.92
619 ....
SO,
4J9 2.00
6.10 1.88
1.90
2.25 13.28
1.80 12.39
1.63 12.07
1.55 11.91
1.55 11.91
1.50 il.81
I.5C 11.81
1.50 11.81
1.46 11.74
1.29 11.39
1.29 11.39
1.29 11.39
1.29 11.39
1.29 11.3*
0.69 10.22
0.78 10.40
0.85 10.5)
aw ion
0.56 9.97
1.13 4.91
1.17 t.91
1.59 5.31
3.29
0.53 4.6*
'
n
o
cr
c
en
<*
o'
n
o
o
*Curl>oii and sulfur arc cxim-uk-recl as gases fur iiiolal calculations only.
Note: Tliis table is reprinted from Fuel Flue Cases. 1941 Edition,
courtesy of American Cas Association.
All gas volumes corrected to 60 F and 30 in. Hg dry.
-------
Basic Combustion Concepts
Table 4. USUAL AMOUNT EXCESS AIR SUPPLIED TO FUEL-BURNING EQUIPMENT
Fuel
Type of furnace or burners
Excess Air,
% by wt.
Pulverized coal
Crushed coal
Coal
Fuel-oil
Acid sludge
Natural, Coke-oven,
& Refinery gas
Blast-furnace gas
Wood
Bagasse
Black liquor
f Completely water-cooled furnace for slag-tap or
< dry-ash-removal
^ Partially water-cooled furnace for dry-ash-removal
Cyclone furnace - pressure or suction
{Stoker-fired, forced-draft, "B&W chain-grate
Stoker-fired, forced-draft, underfeed
Stoker-fired, natural-draft
JOil burners, register-type
| Multifuel burners and flat-flame
Cone- and flat-flame-type burners, steam-atomized
f Register-type burners
\Multifuel burners
Intertube nozzle-type burners
Dutch-oven (10-23% through grates) and Hofft-type
All furnaces
Recovery furnaces for kraft and soda-pulping processes
15-20
15-40
10-15
15-50
20-50
50-65
5-10
10-20
10-15
5-10
7-12
15-18
20-25
25-35
5-7
E Heat of Combustion
The rapid oxidation of combustible com-
pounds results in the exothermic reaction
(evolution of heat). The heat evolved (Q)
is known as the "heat of reaction" or more
specifically the "heat of combustion. "
The principles involved in the development
of heat by combustion, generally accepted
as authoritative, were propounded by
Bcrthelot. His "second law, " as applied
to combustion in furnace practice, is of
particular interest and may be stated as
follows^': In a furnace (where no
mechanical work is done) the heat energy
evolved from the union of combustible
dements with oxygen depends upon the
ultimate products of combustion and not
upon any intermediate combinations that
may occur in reaching the final result.
The heat of combustion for a number of
substances is shown in Table 3.
Ill TYPES OF FLAME COMBUSTION
A Yellow flame
A luminous (yellow) flame results when
air and fuel flowing through separate
ports are ignited at the burner nozzle.
Combustion occurs over an extended
area in the combustion chamber, pro-
ducing a highly radiant flame. The ex-
pansion of the gases as the flame pro-
gresses provides the necessary
turbulence, while a large combustion
chamber assures the necessary time at
the combustion temperature to complete
the reaction.
B-13
-------
Basic Combustion Concepts
(2)
According to the carbonic theoryv ' (yellow
flame combustion), the hydrocarbon
molecules decompose upon exposure to
the high temperature in the combustion
zone into it's constitutent elements,
carbon and hydrogen, and these then burn
independently, each combining separately
with a part of the oxygen present. Car-
bonic combustion is characterized by a
yellow flame, caused primarily from the
incandescent carbon. Under conditions
of incomplete combustion yellow flame
combustion will deposit quantities of soot
but will not give offensive odors.
B Blue Flame
A burner utilizing the same fuel, but
arranged to premix the air and fuel
prior to delivery to the burner nozzle,
will produce a short, intense, blue flame,
permitting complete oxidation within a
confined space.
According to the hydroxylation theory*2'
(blue flame combustion) the hydrocarbon
molecules upon entering the combustion
zone absorb oxygen in successive stages,
each stage resulting in the formation of
hydroxyl (OH) groups. The intermediate
products of the absorption of oxygen by a
hydrocarbon (hydroxylation) are thus
alcohols and aldehydes. Under the in-
fluence of further heat and temperature
the alcohols and aldehydes burn to carbon
monoxide and hydrogen, and finally to
carbon dioxide and water.
Hydroxylative combustion is characterized
by a blue flame, resulting from the for-
mation of aldehydes and then the burning
of these aldehydes. Under conditions of
incomplete combustion, blue flame com-
bustion gives a strong aldehydic odor, but
will not deposit soot in the combustion
chamber or gas passages.
In any fuel-fired burner, whether it is
of the luminous (yellow flame) or per-
mixed (blue flame) type, sustained com-
bustion depends upon maintaining the
air-gas supply to the burner within the
flammable range.
REFERENCES
1 Babcock and Wilcox Co.
Generation and Use.
Chapter 4. 1963.
Stream -- Its
37th Edition,
Faust, F.H. , et. al.
Burning, p. 173.
Handbook of Oil
B-14
-------
FACTS ABOUT FUELS
L.N. Rowley, J. C. McCabe and B. G. A. Skrotzki*
I GAS
Of many gaseous fuels, only natural gas has
any commercial importance in steam genera-
tion because manufactured gases run too
high in cost. Usually byproduct gases have
low heating values and are produced in
relatively minor quantities. So they are
ordinarily used at the production point and
not distributed.
Natural Gas. The origin is not known but it
is often found associated with oil, and the
two fuels are believed to have a common
source. Natural gas is produced in more
than 30 states and widespread pipeline
networks make it available in some part of
nearly every state.
Natural gas is colorless and odorless. Com-
position varies with source, but methane
(CH4) is always the major constituent. Most
natural gas contains some ethane (CgHg) and
a small amount of nitrogen. Gas from some
areas often called "sour" gas, contains
hydrogen sulphide and organic sulphur vapors.
Heating value averages about 1000 Btu per
cu ft (20, 000 Btu per Ib) but may run con-
siderably higher. Natural gas is usually sold
by the cu. ft. but may be sold by the therm,
which is 1. 000, 000 BTU.
II OIL
Petroleum and its byproducts furnishprac-
tically all commerically used liquid fuels.
Geologists believe decomposition of minute
marine growths or possibly, at times, of
vegetable matter formed the oil that lies
trapped in pools between layers of the earth's
crust. This crude oil consists of 83-87%
carbon and 10-14% hydrogen, plus traces of
oxygen, nitrogen and sulphur. The hydrogen
and carbon are combined as hydrocarbons.
Crude oil moves from well to refinery mainly
by pipeline and tanker. Although virtually
every state boasts some refining capacity,
ten have almost 90% of the nation's total.
Fuel oils move from refineries to nearby
markets by truck, tank car and barge, with
tankers serving seaboard areas.
Refining Processes. Since practically all
liquid fuels are either products or bypro-
ducts of refining, the way they are made
has more to do with their fuel qualities than
the source of the crude. Refining consists
of separating and, usually, recombining the
hydrocarbons of the fuel oil into specialized
products like gasoline, fuel oil, etc. Basic
process is simple distillation, which separ-
ates the hydrocarbons into groups or
"fractions" having the same range of boiling
points. From light to heavy, typical fractions
are; (1) naphtha (2) gasoline (3) kerosene,
and (4) gas oil. These are the distillates;
the remainder, or residual, is a heavy fuel
oil. Products of simple distillation are
called straight-run.
Simple distillation is sometimes the whole
story, but in modern refining it is only the
beginning. To secure greater gasoline
yields, fractions heavier than gasoline are
usually cracked, that is, decomposed by
heat and pressure, with or without a catalyst.
Of the new hydrocarbons resulting, some
are lighter and some heavier; these are
likewise separated according to boiling
range. Cracking, unlike simple distillation,
actually changes the hydrocarbon structure
so crude oil yields more valuable lighter
hydrocarbons (gasoline) and proportionately
less heavy ones.
Commercial Fuel Oils. Fuel oils used
commercially may be either distillates or
residuals, and either straight run or cracked.
Straight-run products become increasingly
less common as refinery practice leans more
*"Fuels and Firing Power" pp. 77-83 (December, 1948.
PA. C. ce. 24. 9. 66
B-15
-------
Facts About Fuels
heavily on cracking, and are, in general,
premium grades. Thus the great bulk
of commercial fuel oils are cracked products;
distillates form the source for lighter grades
used in domestic and some commercial and
industrial burners, whereas residuals supply
the heavy oils for larger commercial and
industrial units.
Refinery wastes, which have little or no
commercial value, are usually burned at the
refinery or in adjacent plants. They include
acid sludge, tars and tank cleanings or
"bottoms. "
Specific Gravity. Since hydrogen has a
much higher heating value and lower atomic
weight than the other principal element in
fuel oil, it's easy to see that the proportions
of carbon and hydrogen affect both specific
gravity and heating value. Because of this,
specific gravity forms a reliable guide to an
oil's heating value.
Specific gravity in degrees API (American
Petroleum Institute) is found by dividing
specific gravity with respect to water (at
60°F)into 141.5 and subtracting 131. 5 from
the answer. Gravity in degrees Baume is
found in the same way except the numbers
are 140 and 130, respectively. For practical
engineering work, the two gravity scales may
be considered the same.
Viscosity. The relative ease or difficulty
with which an oil flows is its viscosity. It
is measured by the time in seconds a
standard amount of oil takes to flow through
a standard orifice in a device called a
viscosimeter. The usual standard in this
country is the Saybolt Universal, or the
Saybolt Furol, for oils of high viscosity.
Since viscosity changes with temperature,
tests must be made at a standard temperature,
usually 100°Ffor Saybolt Universal and 122°
F for Furol.
Viscosity indicates how oil behaves when
pumped and, more particularly, shows when
preheating is required and what temperature
must be held.
X
Flash and Pour. Flashpoint represents the
temperature at which an oil gives off enough
vapor to make an inflammable mixture with
air. Results of a flashpoint test depend on the
apparatus, so this is specified as well as
temperature. Flashpoint measures oil's
volatility and indicates maximum temperature
for safe handling.
Pour point represent lowest temperature at
which an oil flows under standard conditions.
Including pour point in a specification insures
that an oil will not give handling trouble at
expected low temperature.
By centrifuging a sample of oil, amount of
water and sediment can be found. These are
impurities and while it is not economical to
eliminate them, they should not occur in
excessive quantities (not more than 2%). In-
combustible impurities in oil, from natural
salts, from chemicals in refining operations,
or from rust and scale picked up in transit,
show up as ash. Some ash-producing
impurities cause rapid wear of refractories
and some are abrasive to pumps, valves and
burner parts. In the furnace, they may form
slag coatings.
All tests above are covered by ASTM stand-
ards, which should be consulted for details
of apparatus and methods (ASTM Standards
on Petroleum Products and Lubricants,
American Society for Testing Materials,
1916 Race St, Philadelphia 3, Pa.).
Fuel oils have a tendency to deposit sludge
in storage; this may be aggravated by mixing
oils of different character as when deliveries
from two sources go into the same tank.
These simple rules avoid trouble when oils
are mixed: (1) Straight-run residuals can
be mixed with any straight-run product,
and cracked residuals with straight-run
residual (2) cracked distillate can be added
as a third constituent, but (3) cracked
residual cannot be added to straight-run
distillate.
B-16
-------
Facts About Fuels
III COAL
Three-hundred-million years ago, in swamp
forests of the Carboniferous Age, the founda-
tion of our present reserves was laid. For
50 million years, giant trees and ferns grew
and fell, to decay and form rich peat bogs.
Floods buried the bogs under layers of
sediment, only to subside and permit the
growth-and-decay cycle to begin again. As
millions of years passed, pressure, heat
and time worked to drive off some volatile
matter, to harden the mass, and to turn it
into the carbon-substance we call coal.
Different kinds contain different amounts
of carbon substance depending on the age of
the deposit and the conditions under which it
formed. Next to the original peat, the
"youngest" form is lignite, high in moisture
and low in fixed carbon. Older coals,
higher in "rank, " contain more fixed carbon.
Analyses. Various tests and methods of
analysis express coal qualities in figures
instead of words. Principal characteristics
are expressed in what is known as a proxi-
mate analysis, as distinguished from an
ultimate analysis, which shows the exact
chemical composition of a fuel, without
paying any attention to the physical form in
which the compounds appear. As we have
seen, this gives data needed for combustion
calculations.
For a better picture of coal1 s behavior in a
furnace, the proximate analysis determines
the percentage of (1) moisture (2) ash (3)
volatile matter and (4) fixed carbon. These
percentages add up to 100. In addition, it
is customary to determine; (1) total amount
of sulphur, as a separate percentage ( 2) ash-
fusion temperature, and ( 3) heating value.
Reporting Analyses. There are five ways
to report an analysis, although only the
first three are likely to be met in power-
plant work: (1) as received (2) air dried
( 3) moisture free (4) moisture and ash free,
and (5) moisture and mineral free. As the
name implies, the as-received analysis re-
ports the condition of coal as delivered to
the laboratory. This comes closest to
giving the conditions as shipped or as fired,
the values desired in practical work. Loss
or gain of moisture between time of sampling
and analysis depends on the kind of coal, size,
weather conditions, and method of handling
sample.
Following paragraphs discuss the various
characteristics of coal (those reported in
proximate analyses and others) and how
they affect the value of coal in power-plant
operation. For details on equipment and
procedures for testing coal, consult ASTM
Standards on Coal and Coke (1948).
Moisture. All coal contains some natural
moisture (1 to 5% in Eastern coals and up
to 40% in some lignites). This inherent
moisture lies in the pores and forms a true
part of the coal, being retained when it is air
dried. Surface moisture depends on condi-
tions in the mine, and during transit.
Moisture must be transported, handled and
stored; its presence in large amounts in-
creases cost and difficulty of these opera-
tions. Looked at another way, moisture
replaces an equal amount of combustible
material and thus decreases the heat content
per Ib. In addition, some heat liberated in
the furnace goes to evaporating moisture in
the fuel and superheating the vapor.
A Mineral Impurities
Ash. .This incombustible mineral matter,
left behind when coal burns completely,
differs from "ashes, " as the power-plant
man knows them, because ashes taken
from a furnace always contain some un-
burned coal.
Like moisture, ash is an impurity that in-
creases shipping and handling costs. It
must be removed from the furnace and the
plant, usually requiring additional equip-
ment and expense. Recent research shows
that amount and character of ash constitutes
the biggest single factor in fuel-bed and
furnace problems like clinkering and
slagging. An increase in ash content
usually means an increase in carbon
carried to the ashpit.
B-17
-------
Facts About Fuels
Volatile Matter. In a way not yet clearly
known, coal holds combustible gases such
as methane and other hydrocarbons, hy-
drogen and carbon monoxide, and incom-
bustible gases Hke carbon dioxide and
nitrogen. Heat releases these gases.
Percentage of volatile matter indicates
the amount of gaseous fuel present and
thus bears a direct relationship to firing
mechanics. It affects furnace volume and
arrangement of heating surfaces.
Fixed Carbon. When the volatile matter
distills off, a solid fuel is left, consisting,
in the main, of carbon, but containing
some hydrogen, oxygen, sulphur and
nitrogen not driven off with the gases.
Subtracting percentage of moisture, ash
and volatile matter from 100% yields a
percentage called fixed carbon.
Sulphur. Although it burns, sulphur in
coal is an undesirable element for power-
plant use. It plays a part in clinkering
and slagging, in corrosion of air heaters,
economizers, breeching and stacks, and
in spontaneous combustion of stored coal.
It occurs mainly as iron sulphide
(commonly known as pyrites), as organic
sulphur, and in small amounts as sulphates.
Only total sulphur is measured, although
it is known that iron combined with the
sulphur shares the blame for troubles
laid to sulphur.
Ash Fusion. Temperature at which ash
fuses is measured by heating cones of ash
in a furnace arranged to produce a reduc-
ing atmosphere. Temperature at which
the cone fuses down to a round lump is
called softening or ash-fusion temperature.
Other temperatures sometimes observed
include that at which (1) cone tip starts
to bend (initial deformation temperature)
and (2) cone spreads out in a flat layer
(fluid).
Ash-fusion temperature (and sometimes
the spread between initial and softening,
or softening and fluid temperatures)
serves as the best single indicator of
clinkering and slagging tendencies under
given fuel-bed and furnace conditions.
Heating Value. If a coal sample is
burned in a "bomb" calorimeter filled
with oxygen under pressure, the higher
heating value is measured. The consumer
buys energy units when he buys fuel, and
so the heating value plays a basic part
in judging fuel values. Sometimes heating
value of fuel may affect maximum capacity
of a plant.
B Pulverizing Qualities
Grindabiiity. Wide use of pulverized-
fuel firing brought a need for tests to
show the relative ease or difficulty of
grinding different kinds of coal. AsTM
tentatively approves two methods, ball-
mill and Hardgrove. The first measures
relative amounts of energy needed to
pulverize different coals by finding the
number of ball-mill revolutions needed
to grind a sample so 80% passes a 200-
mesh sieve (74 microns). The ball-mill
grindability index, in percent, is found by
dividing number of revolutions into
50,000.
In the Hardgrove test, a prepared sample
receives a definite amount of grinding
energy in a miniature pulverizer; results
are measured by weighing amount passing
a 200-mesh sieve. Multiplying weight
passing the sieve by 6. 93 and adding 13
to the product gives Hardgrove grindability.
Grindability values do not give a direct
comparison of pulverizer capacity or
power requirements. The latter are
affected by size and type of pulverizer,
and by feed size, moisture and fineness.
The operator should check behavior of
coals in his pulverizer against standard
indices to establish a relation between
pulverizer performance and grindability.
Caking, Coking. Considerable confusion
exists regarding proper use of these two
terms. Heating coal drives off volatile
matter, leaving behind practically pure
carbon. This is coke. It may take the
form of small powdery particles or may
fuse into lumps of varying size and strength.
Swelling may occur. In commercial coke-
making, "coke" generally refers to lumps
of marketable size; coking coals make them.
B-18
-------
Facts About Fuels
Coke formation, in one shape or another,
represents an intermediate combustion
stage in any fuel bed; the' difference lies
in whether a plastic stage occurs and
lumps of coke form. Coals that become
plastic and form lumps or masses of coke
are called caking coals while those that
show little or no fusing action are free-
burning.
Caking properties of a coal and the nature
of the coke masses formed (size, strength,
etc.) are valuable indicators of behavior
in fuel beds. A recently adopted test
measures free-swelling index and a pro-
posed test determines agglutinating value,
and approximate measure of that material
in coal that fuses and becomes plastic.
C Sizing of Coal
Size stability. Ability of coal to resist
breakage is size stability; its opposite
is friability, the tendency to break or
crumble into smaller pieces. Where
plant conditions make size an important
factor, friability must be considered to
get a rough idea of the difference likely
to exist between size as shipped and as
fired. ASTM has two tentative tests for
these complementary properties: (1)
drop-shatter test indicates resistance
to breakage from ordinary handling (2)
tumbler test, the effect of rougher handling
in mechanical conveyors, feeders, etc.
Anthracite Sizes. Standard sizes are:
broken, passing a 4 3/8-in. retained on
3 1/4 in.; egg, 3 1/14 to 2 7/16; stove,
2 7/16 to 1 5/8; chestnut, 15/8to 13/16;
pea, 13/16 to 9/16; No. 1 buckwheat, 9/16
to5/16; No. 2 buckwheat (barley), 3/16to
3/ 32. Culm or river coal is refuse from
screening anthracite into prepared sizes.
It is now often dredged from rivers into which
it was originally dumped.
Bituminous Sizes. There is little stand-
ardization of either screen openings or
names given to sizes. Run of mine is un-
screened coal as it comes from the mine;
a steadily decreasing amount is shipped
today because of demand for prepared
sizes for domestic stokers, etc. Screen
openings usually designate sizes. A
"2-in. nut-and-slack" normally means
all coal passing a 2-in. screen; amount of
different sizes present may vary widely.
Occasionally a limitation is placed on
percentage of fines. So-called between-
screen sizes (everything passing one
screen and retained on another) give a
closer idea unless spread between screens
is large. Coal size affects fuel-bed
nature, draft required, density of coke
formed, amount of unburned-carbon loss.
D Preparation, Storage
Coal Preparation. Many producers now
offer cleaned or washed coals as products
having a higher value to users. Cleaning
or washing removes impurities and so
lowers ash content; it also tends to reduce
sulphur in the form of pyrites and raise
ash fusion.
Treating coal with refined petroleum
oils of 100-600 ssu, or blends of petro-
leum products, allays dust nuisance in
handling by eliminating most of the fine
dust and much of the coarse. Treatment
remains effective more than a year, even
in outdoor storage. Experience seems
to show that oil treatment reduces both
moisture absorption of coal and freezing
troubles. Tests show it does not increase
spontaneous heating, nor appreciably
affect burning.
Storing. Coal exposed to atmosphere
combines with oxygen, liberating heat.
Such slow oxidation is called weathering.
It dulls the appearance of coal, causes
reduction in size, impairs firing and
coking qualities, and lowers heating
value. These changes are practically
unnoticeable for anthracite, and slight for
most bituminous coals. Low-rank bitu-
minous coals and lignite suffer more
markedly. Loss of heating value over a
5-year period might run 1-3% for West
Virginia and Pennsylvania coals, 4-6%
for Illinois.
B-19 and B-20
-------
OIL BURNING EQUIPMENT*
In addition to proportioning fuel and air, and
mixing them, oil burners must prepare the
fuel for combustion. There are two ways of
doing this, with many variations of each:
(1) The oil may be vaporized or gasified by
heating within the burner, or (2) it may be
atomized by the burner so vaporization can
occur in the combustion space.
Designs of the first group, usually called
vaporizing burners, are necessarily limited
in the range of fuels they can handle and find
little power use.
If oil is to be vaporized in the combustion
space in the instant of time available, it
must be broken up into many small particles
to expose as much surface as possible to the
heat. This atomization may be effected in
three basic ways by: (1) using steam or air
under pressure to break the oil into droplets
(2) forcing oil under pressure through a
suitable nozzle, and (3) tearing an oil film
into drops by centrifugal force. All three
methods find use in practical burners.
Turbulence Necessary. In addition to break-
ing the oil into small particles for fast vapor-
ization, the burner must provide motion
between oil droplets and air, so vapor "coats"
are stripped off as fast as they form and
fresh surfaces exposed. This calls for pene-
tration of the oil particles in the proper
direction and for a high degree of turbulence
in the air. Such relative motion of oil and
air helps to produce more uniform mixture
conditions over the combustion zone.
Hydrocarbons burn by hydroxylation and by
cracking. In practice, both forms are pre-
sent, although the usual oil-burner flame is
predominantly the latter type. This charac-
teristic short yellow flame has good radiating
characteristics and fits usual combustion
spaces well. It carries, however, solid
carbon particles, which, if their burning is
stopped by any chilling action, form soot.
Depending on the nature of the chilling, the
soot may deposit on heating surfaces or may
be carried out the stack as a major consti-
tuent of smoke.
Pure hydroxylative burning, while free from
soot and smoke possibilities, yields a less
radiative flame and can be produced only in
certain types of burners. Thus, as in many
engineering matters, we compromise and
strive to introduce enough hydroxylation in-
to a predominantly cracking process to keep
the flame clean and reduce smoking ten-
dencies. Hydroxylation is encouraged by
thorough atomization, suitable preheating
of both oil and air, and exposing the mixture
to a gradually increasing temperature over
not too short a time.
A Steam-Atomizing Burners. Let's look
now at practical oil-burning equipment.
Oldest form is the steam- or air-atomizing
burner. Installation is relatively inex-
pensive and simple, especially where no
attempt is made to control steam and oil
supply simultaneously. Steam-atomizing
burners, as a class, possess ability to
burn almost any fuel oil, of any viscosity,
at almost any temperature. Air is less
extensively used as an atomizing medium
because its operating cost is apt to be
high.
These burners can be divided into two
types: (1) internal-mixing or premixing -
oil and steam or air mix inside the body
or tip of the burner before being sprayed
into the furnace, Figs. 2, 4, and
(2) external-mixing - oil emerging from
the burner is caught by a jet of steam or
air, Figs. 1, 3.
Steam consumption for atomizing runs
from 1 to 5% of steam produced, usually
averaging around 2%. Pressure required
varies from about 75 to 150 psi, and
steam can be taken from: (1) a low-
pressure line (2) a desuperheater with a
pressure reducer, or (3) a drum vent,
through an orifice and regulating valve.
Oil pressure need only be enough (usually
10 to 15 psi) to carry oil to the burner tip.
External Mixing. In the burner of Fig. 1,
oil reaches the tip through a central pass-
age, flow being regulated by the screw
*Based on the publication by: Rowley, L. N., McCabe,
J. C. and Skrotzki, B.C. A., "Fuels and Firing", Power,
pp 85-88 (December, 1948).
PA. C. ce. 26. 9. 66
B-21
-------
Oil Burning Equipment
STEAM OR AIR ATOMIZING OIL BURNERS
Air or sttoat supply
v*-atlen llnds relatively little
use because cost Is often high
spindle, right. Oil whirls out against
a sprayer plate to break up at right angles
to the stream of steam, or air, coming
out behind it. The atomizing stream
surrounds the oil chamber and receives
a whirling motion from vanes in its path.
When air is used as the atomizing medium
in this burner, it should be at 10 psi for
lighter oils and 20 psi for heavier. Com-
bustion air enters through a register,
shown below in Fig. 1. Vanes or shutters
are adjustable to give control of excess
air. Fig. 3 shows another external-
mixing design. Oil and steam discharge
through separate nozzles at right angles
to each other, the steam breaking up the
oil stream.
Internal Mixing. Figs. 2 and 4 give
examples of the premixing principle. In
Fig. 2, steam and oil meet and mix well
within the burner body. Energy in the
steam serves to force the steam-oil
mixture through the nozzle for atomization.
Burner of Fig. 4 brings oil and air under
pressure together at the burner tip for
mixing before discharge into the furnace.
B Mechanical Atomizing. Now let's look
at another major burner class, mechan-
ical atomizers, Figs. 5 to 8. Good atomi-
zation results when oil under high
pressure (75 to 200 psi or higher) is
discharged through a small orifice, often
aided by a slotted disk. The disk gives
the oil a whirling motion before it passes
on through a hole drilled in the nozzle,
where atomization occurs. For a given
nozzle opening, atomization depends on
pressure and, since pressure and flow
are related, best atomization occurs
over a fairly narrow range of burner
capacities (about 40%).
To follow a fluctuating boiler load, a
number of burners may be installed and
turned on or off as steam demand varies;
or burner tips with different nozzle open-
ings can be applied to a single burner
body.
Wide-Range Designs. Oil-burner manu-
facturers have developed many designs
to extend the usual 1. 4 to 1 capacity'range
of the mechanical-atomizing nozzle. One,
B-22
-------
Oil Burning Equipment
for example, features a plunger that
opens additional tangential holes in the
nozzle as oil pressure increases. This
gives a 4 to 1 range. Another design,
Fig. 6, employs a movable control rod,
which, through a regulating pin, varies
the area of tangential slots in the sprayer
plate and the volume of oil passing the
orifice.
Still another variable-capacity design,
Fig. 7, delivers oil at high pressure
(350 psi) at a constant rate, but discharges
through the nozzle only the quantity needed
to meet steam demand. The remainder
recirculates.
Fig. 8 shows a wide-range mechanical
atomizer which, when combined with
either of the pumping systems shown in
Fig. 9, will give a capacity range of
about 15 to 1, and considerably higher if
needed. By use of either a constant-
differential valve or pump, as shown,
difference in pressure between supply
and return is held constant. This main-
tains a uniform pressure drop across
the tangential slots in the burner tip and
creates a constant atomizing force. The
valve system is simple to install and
maintain, but the pump system offers
advantages in many plants: (1) No hot
oil is returned to storage tank or pump
suction. (2) Fuel enters the closed cir-
cuit at the same rate it is burned, sim-
plifying fuel metering and combustion
control. (3) Pump may be used to boost
pressure on existing oil-burner systems.
MECHANICAL ATOMIZING OIL BURNERS
5 KUchanlcal-afomlilng burner reeel»ei the oil under
preuure, about 315 lo 3OO ptl, Old ot an optimum
viicoilty of about ISO »«u. Orifice atomlm Hi* ftral
6 With fl»d orlllee
!. b«flt atoml-
cntlen occurs In narrow
flow rang*. D*llgn at
right obtain! wldo ca-
pacity rang* by lupply-
Ing oil to burnor tip
ot a constant rat* In
«*ll *f demand. OH
bwrn*d varl*i with th*
load, rost U returned
7 Movable control rod, center, through a regulating
pin, vorlei th* or.a of tangential .lot. In Iprayer
plot* and v*lum* of oil palling through orlflc*, right.
With oil kept al 30O p.I and 1OO nu, rang* li 1O to I
g Wide-range burn-
er obov* operate*
an comtant-dlfferentlol
yttem*
B-23
-------
Oil Burning Equipment
Figure 9. How One Wide-Range
Mechanical Atomizing
Oil Burner System Operates
Regulation of owlput from tho
wldo-rango burner
whoto otomlifng 6nd whirling ond
howi above, can
-------
Oil Burning Equipment
ROTARY CUP ATOMIZING OIL BURNING
oil swirls
counter clockwise
air
10 Cup revolving counterclockwise
breaks up all film at rim by
centrifugal force and discharges
into a clockwise air stream
11 Built-in fan rotating at motor-
speed supplies primary air just
behind the atomizing oil cup.
Air catches up fine oil spray
leaving at cup edge
12 Belt driven rotary-cup burner
carries a fuel-oil reservoir
to insure positve feed, and
a submerged electric heater to
hold oil at correct temperature.
Gas pilot mounted overhead, together
with low-voltage system, serves
to ignite the oil
B-25 and B-26
-------
COAL BURNING EQUIPMENT
I UNDERFEED STOKERS, SINGLE-RETORT,
RESIDENTIAL
In the residential underfeed stoker, the coal
is fed from a hopper or directly from the coal
storage bin to the retort by a continuous,
rotating screw (see Figure 1). Coal rises
into the firing zone from underneath, thus
the term "underfeed firing." Air is delivered
to the firing zone through tuyeres (grate
openings), also from underneath the actively
burning bed. The coal and primary air con-
trol is "all on" or "all off. " Ash is removed
as a clinker from a refractory hearth through
the furnace firing door. Burning rates range
from 1 to 60 pounds of coal per hour.
Figure
Residential underfeed stoker
II
UNDERFEED STOKERS, COMMERCIAL,
INSTITUTIONAL, AND SMALL INDUSTRIAL
The general arrangement is as described in
the previous paragraph, with "dead" plates
replacing the refractory hearth (Figure 2).
As sizes become larger, screw feeders are
replaced by a mechanical ram, which feeds
coal to pusher blocks that distribute the coal
in the fire box. Ash is discharged by side-
dump grates. Modulating combustion controls,
i. e., variable control of both fuel and air
rates, are often used. Forced draft is auto-
matically regulated, and separate over fire-
air systems are used, particularly when on-
off controls are used. A bridge wall retains
the coal over the stoker grates. The size
ranges for screw-feed stokers are 60 to
1, 200 pounds of coal per hour and for ram-
feed stokers, from 300 to 3, 500 pounds per
hour.
llllllll uyj
USHEBJ ,,£~Zr
BLOCK Vv ROD ~^J ^y
£
LONGITUDINAL SECTION
Figure 2. Single-retort underfeed stoker.
MULTIPLE-RETORT UNDERFEED
STOKERS
As the name implies, these units usually con-
sist of several inclined retorts side by side,
with rows of tuyeres in between each retort
(Figure 3). Coal is worked from the front
hopper to the rear ash-discharge mechanism
by pushers. The forced-air system is zoned
beneath the grates by means of air dampers,
and the combustion control is a fully modu-
lating system. In the larger furnaces the
walls are water-cooled, as are the grate
surfaces in some units. Multiple-retort
underfeed stokers are losing their popularity,
giving way to spreaders and traveling-grate
units. Sizes range from 20, 000 to 500, 000
pounds of steam per hour with burning rates
up to 600, 000 Btu per square foot of grate
per hour.
IV TRAVELING-GRATE AND CHAIN-GRATE
STOKERS
Traveling-grate and chain-grate units (Figure
4) are essentially moving grate sections,
*Based on the publication by: Smith, W. S., and Gruber, C. W. Atmospheric Emissions from
Coal Combustion - An Inventory Guide. Public Health Service Publication No. 999-AP-24,
April, 1966.
PA.C.ce.27.9.66
B-27
-------
Coal Burning Equipment
COAL HOPPER
COAL RAMS
ASH-
DISCHARGE PLATE
FUEL
DISTRIBUTORS
Figure 3. Multiple-retort underfeed stoker.
COAL HOPPER
COAL GATE
HYDRAULIC
DRIVE
through an automatic combustion-control
regulator. Grate heat release may range
from 350, 000 to 500, 000 Btu per square foot
per hour. The size range for this unit is
from 5, 000 to 100, 000 pounds of steam per
hour.
VI BCR* AUTOMATIC "PACKAGED"
BOILER
This unit is a complete steam or hot water
generating system, incorporating a water-
cooled vibrating grate as the firing mechanism
(Figure 6). Coal is delivered from the storage
bin to a hopper from which it travels on the
vibrating grate to the fuel bed. Ash is dis-
charged automatically with a screw conveyor.
The unit has completely automatic conbustion
controls so that coal feed to the hopper from
the bin and ash discharge is coordinated with
load conditions. Forced and induced draft fans
are used. The size range is from 3 to 20
million Btu per hour input.
Figure -4. B A W jet-ignition chain-grate stoker.
moving from the front to the rear and carry-
ing coal from the hopper in front through a gate
into the combustion zone. The fuel bed burns
progressively to the rear, where the ash is
continuously discharged. Older units with
natural draft are fast disappearing; modern
units have zone-controlled forced draft. Com-
plete combustion-control systems are utilized,
and overfire air, especially in the front wall,
is an aid to burning the volatiles in the fuel.
Units range in size from 20 to 300 X 106 Btu
per hour input.
COAL HOPPER -
COAL GATE!
OVERFIRE-AIR HOZZLES
Figure -5. Vibratinq-qrate stoker furnace.
V VIBRATING-GRATE STOKER
This unit consists of a water-cooled grate
structure on which the coal moves from the
hopper at the front of the boiler through the
burning zone by means of a high-speed vibrating
mechanism automatically operated on a time-
cycling control (Figure 5). As in the traveling
grate, the fuel bed progresses to the rear,
where the ash is continuously discharged.
Forced air is zone-controlled and regulated,
along with the complete coal and air system.
VII SPREADER STOKER
The spreader stoker combines suspension
and fuel bed firing by the stoker mechanism
feeding from the hopper onto a rotating flipper
mechanism, which throws the fuel into the
furnace (Figure 7). Because fuel is burned
partly in suspension and partly on the grate,
the fuel bed is thin, and response to fluctu-
ations in load is rapid. The grates are either
*Bituminous Coal Research, Inc.
B-28
-------
Coal Burning Equipment
similar to those used for liquid fuel (Figure
8). In direct-firing systems; raw coal is dried
and pulverized simultaneously in a mill and
is fed to the burners as required by the
furnace load. The control system regulating
the flow of both coal and primary air is so
designed that a predetermined air-coal ratio
is maintained for any given load. The in-
directly fed unit utilizes storage bins and
feeders between the pulverizers and the
burners. Some bin-and-feeder systems are
in use, but the majority of plants use direct-
firing units.
Figure -6. Bituminous Coal Research, Inc., packaged boiler
Radiant superheater
GRATE
Figure -7. Spreader stoker-fired furnace.
stationary or continuously moving from the
rear to the front. Vibrating, oscillating,
traveling, and chain grates are designed for
moving the fuel toward the ash receiving pit.
Zoned undergrate air is important, as is the
careful application of a responsive combustion
control system. Overfire air is necessary. Fly-
ash carry-over is stronglyinfluencedbyhigh
burning rates, whereas smoke emission is
increased at low burning rates. In large
units, cinders are often returned to the grate
from the fly-ash collector to reduce unburned
carbon losses. Spreader stokers range in
size from 6 to 500 X 106 Btu per hour input
or from 5, 000 to 400, 000 pounds of steam
per hour output.
VIII PULVERIZED-FUEL FIRING UNITS
In this sytem, coal is pulverized to particles,
at least 70 percent of which pass through a
200-mesh sieve, and is fired in burners
Figure -8. Pulverized-coal-fired
unit.
Burners are characterized by their firing
position, i.e., horizontal, vertical, or
tangential (see Figure 9). Arrangements for
the introduction of primary, secondary, and,
in some cases, tiertiary air vary with
burner manufacturers. One manufacturer
uses an adjustable burner, which is tilted
upward or downward to control the furnace
outlet temperature, so that steam temperature
can be regulated over a wide range of
capacities.
Pulverized-coal-fired units are usually one
of two basic types, wet bottom or dry
bottom. The temperature in a wet-bottom
furnace is maintained above the ash fusion
temperature, thus the slag is melted so
that it can be removed from the bottom as a
liquid. The dry-bottom furnace maintains a
temperature below this point so that the ash
will not fuse.
B-29
-------
Coal Burning Equipment
Pulverized-fuel-fired boilers range in capacity
from 200, 000 to several million pounds of
steam per hour.
PRIMARY AIR_-_(ERTIARy
AND COAL
PRIMARY AIR
NO COAL
FAN1AIL MULTIPLE INTEHTUBE
(a) VERTICAL FIRING
PLAN VIEW Of FURNACE
(b) TANGENTIAL FIRING
(c) HORIZONTAL FIRING
(e) OPPOSED*INCLINED FIRING
Figure 9. Various methods of firing coal
in suspension
IX CYCLONE FURNACE
The cyclone furnace is a water-cooled hori-
zontal cylinder, in which the fuel is fired
and heat is released at an extremely high
rate for the given volume (Figure 10). Coal
is crushed so that approximately 95percent
passes through a 4-mesh screen. Coal is
introduced into the burner end of the cyclone,
and air for combustion is admitted tangentially.
Combustion occurs at heat-release rates of
500, 000 to 900, 000 Btu per cubic foot per hour
at gas temperatures sufficiently high to melt
a high percentage of the ash into a liquid
slag, which is discharged from the bottom of
the furnace through a slag tap opening. The
size range of boilers fired are comparable to
those with pulverized-fuel units.
SCREENED-FURNACE OPEN-FURNACE
ARRANGEMENT ARRANGEMENT
OPEN-FURNACE
ARRANGEMENT
Figure 10. Types of cyclone furnaces
REFERENCES
1 de Lorenzi, O. Combustion Engineering.
1st ed. Combustion Engineering-Super-
heater, Inc. New York. 1952.
2 Steam - Its Generation and Use. 37th ed.
The Babcock and Wilcox Co. New
York. 1963.
3 Shields, C. D. Boilers, Types, Char-
acteristics and Functions. F. W. Dodge
Corp. New York. 1961.
4 Perry, J. H. Chemical Engineers'
Handbook. 4th ed. McGraw-Hill, Inc.
New York. 1963.
B-30
-------
DESIGN OF COAL COMBUSTION EQUIPMENT
F. S. Scott*
Environmental Health Services
Maryland State Department of Health
Firing Equipment
There are many ways of burning coal to provide
heat from open burning outdoors to the most
sophisticated pulverized coal installation.
well as "Dutch Oven" type furnaces. This type
of furnace had four refractory walls and a re-
fractory top. The boiler was set in back of the
furnace. Sometimes steam jets were used to
promote combustion.
Hand Firing
Hand firing of coal has many disadvantages and
very few advantages. It can be accomplished with
little smoke but ihis is not the usual case. Hand
firing was used extensively from the time coal
was discovered until early in this century. It is
found only occasionally now.
Overfeed Stokers
The overfeed type of stoker operated by hand was
the earliest mechanical apparatus for this pur-
pose. It was in use sometime early in the 19th
century.
In its early form it consisted of a steeply inclined
grate with alternate stationary and movable sec-
tions. The movable sections were connected
through a linkage to a lever outside of the fur-
nace. The coal was allowed to fall on or move
onto the top of the grate. The operator would
periodically shift the external lever. This moved
alternate grates and caused the coal to travel
down the grate toward the ash pit. A refractory
arch was provided at the front to reflect heat into
the coal bed thus promoting ignition and driving
off the volatile material. In later years, the ex-
ternal lever was connected to a steam engine so
that the grate bars were made to move back and
forth continuously. The frequency of movement
could be varied so that the burning rate might be
controlled. Some very early applications of
secondary air jets were applied to this equipment.
Very few if any stokers of this kind were installed
after 1910. Natural draft from a stack was used.
The next development was the "Murphy" or "V"
type overfeed. As the name implies, the coal
was allowed to flow from hoppers on each side to
the steeply (about 45° angle) sloping grate. It had
a power driven feeder and grate bars. A further
development was the application of a clinker
grinder at the bottom of the "V". This equipment
would burn more coal than could be burned by the
single overfeed or by hand feeding and so was
used with larger boilers. Arches were used as
''Formerly Consulting Engineer, National Coal
Association, Washington, D. C.
Traveling Grate Stokers
The traveling grate or chain grate stoker was
developed about the middle of the 19th century.
It consists of a coal hopper with a "guillotine"
type gate to control the coal feed. The grate
surface is composed of small links or bars
supported in various ways and arranged like an
endless belt over sprockets at either end. The
traveling grate was first moved by a steam
engine and later by an electric motor or tur-
bine. Coal falls from the hopper onto the grate
and the grate moves the coal through the furnace
where it burns. The ash is dropped off the grate
at the rear into the ash pit. Furnace arches of
refractory material are used to promote com-
bustion (both front and rear).
Initially the air was supplied by natural draft.
Present day traveling grate stokers use forced
draft with several, separately controlled, air
zones or wind boxes. They are installed in
water cooled furnaces and sometimes have little
or no front arches. Secondary air jets are
always used, although the size and location may
vary. Traveling grates are used extensively
with "free burning", high ash, high volatile
coals or with anthracite and with boilers up to
250,000 Ib of steam per hour.
Underfeed Stokers
The underfeed stoker was initially developed
about the turn of the century. It was and still is
made in two basic forms the single retort and
multiple retort. The single retort underfeed
stoker is composed of a coal hopper, one feed
trough or retort containing a feeding device (a
screw or piston or ram) with the grate above it.
The grate may end in a dumping plate at each
side or a refractory hearth. This stoker moves
coal in three directions: (1) From front to rear
in the retort, (2) from retort upward to the grate
and burning zone and (3) sideways through the
burning area to ash pits at the sides. The single
retort stoker promotes smokeless burning with
a wide range of coals and is still widely used
with smaller boilers.
B-31
-------
of Coal Combustion Equipment
Multiple Retort Stokers
The early multiple retort underfeed stoker was
an extension of the single retort stoker. It had
one coal hopper across several parallel retorts.
Each retort was fed by a steam driven ram or
piston which in addition moved a series of wedges
or pushers in the bottom of each retort to assist
the fuel movement toward the rear of the furnace,
where the ash was dumped into the ash pit. Air
was introduced between the retorts and at the top
of each retort. The coal moved down each tuyere
row as it burned. The ash was dumped periodi-
cally from the rear to an ash pit. The grates were
set at a small angle to the horizontal, no more
than 25°. Later the pistons or rams were con-
nected to a crankshaft which was turned through
gear reductions by a motor, a turbine or a steam
engine. A further development provided continu-
ous discharge of the refuse by using (1) a clinker
grinder in a pit or (2) a variable slot in the rear
water wall of the furnace. These later stokers
had an overfeed section added to them to increase
capacity and efficiency. Zoned air control was
used. These stokers required forced draft fans.
They are now used with boilers from 25, 000 Ib of
steam per hour to 400, 000 Ib of steam per hour,
single ended, and up to 500, 000 Ib of steam per
hour double ended. They have been built up to
18 retorts wide.
Spreader Stokers
The spreader stoker was developed about the
middle of the 19th century, but it did not have
great acceptance until after World War I. This
stoker consists of a coal hopper and a feeding
mechanism to move small amounts of coal into
a device that injects the coal into the furnace.
This device may be an air stream, a steam jet
or several forms of rotating flippers. The ro-
tating flipper design is the type most used. The
coal is thrown into the furnace and partly burned
in suspension. The larger particles fall to the
grate and are burned there. The grate can be of
four forms (1) flat grate (which must be cleaned
periodically by hand), (2) dumping grate (which
dumps the ash to a pit below the stoker, (3) vi-
brating or oscillating grate (timed, quickly
moving grates) with automatic discharge of ash
to an ash pit at the front of the stoker, and
(4) traveling grate (automatically discharges
refuse to an ash pit usually at the front of the
stoker). Secondary air jets and forced draft are
mandatory.
This method of firing is used with boilers from
5, 000 Ib of steam per hour to 400, 000 Ib of steam
per hour.
Vibrating Grate Stokers
The vibrating grate stoker is a relatively new
development that occurred in the mid 1940's. It
is of the overfeed type. The coal hopper allows
coal to drop to a feeder which pushes the fuel
onto the top of a water cooled grate that slopes
at 17° toward the rear. This grate is composed
of bars placed in contact with tubes in which
boiler water circulates. This assembly is made
to vibrate rapidly, at controlled times depending
on load. The fuel bed moves to the rear and
discharges the refuse automatically to the ash
pit. Secondary air jets and a short ignition arch
are used. It has been used with boilers up to
100,000 Ib of steam per hour.
Pulverized Coal
The use of pulverized coal on a commercial
scale started in the early 1920's. The coal is
ground to a size such that 70% or 80% will pass
through a 200 mesh sieve. This finely crushed
coal is blown into the furnace where all of it is
burned in suspension. There are two methods
of grinding and feeding in use: (1) the coal is
ground to the desired size then placed in a
bunker from which it is transported to a multi-
plicity of burners or (2) each boiler has one or
more mills or grinders that produce the fine
coal as needed. The latter method is most used
today. Originally, pulverized coal was used in
boilers from about 20, 000 Ib of steam per hour
upward. At present it is used with boilers of
100, 000 Ib of steam per hour up to the lar-
gest made. The furnaces may be wet bottom
(the ash is melted and removed as a liquid) or
dry bottom. Forced draft and induced draft
fans are used.
Cyclone Burners
Cyclone firing, a later development by the
Babcock & Wilcox Company, is a modification
of suspension burning. Coal is crushed to pass
a 1/4-inch screen, then introduced into a water-
cooled cylinder 8 ft to 10 ft in diameter. Forced
air is added tangetially at a high velocity causing
the coal and air to swirl in a cyclonic manner
as it burns. Most of the ash is melted and runs
out of the cyclone to the bottom of the furnace
where it is removed as a liquid. Some furnaces
have more than one cyclone. This firing method
has been used with boilers of 100, 000 Ib per
hour and larger.
Heat Utilization Equipment
The heat exchange equipment used with coal
firing can be placed in five categories: (1) fur-
naces or radiant heat absorbers, (2) boilers or
B-32
-------
Design of Coal Combustion Equipment
convection heat exchangers, (3) superheater or
gas-to-vapor heat exchangers, (4) economizers
or added convection heat exchangers and (5) air
heaters or gas-to-heat exchangers. The last two
of these are often called heat traps.
Initially, furnaces were all refractory lined and
used as a combustion zone only. High tempera-
tures, slag and often corrosive gases caused high
maintenance. This led to lining furnace walls and
roofs with water-cooled surfaces. They then
transmitted radiant heat to the water and into
steam through radiant superheaters.
The convection section, the boiler, has been made
in many forms. The earliest boilers were tanks,
containing water, under which a fire was built.
Next a large tube was put through the tank. The
combustion gases were led around the tank and
through the tube. Later, a multiplicity of
smaller tubes (1" or 3" I. D. ) was used. A boiler
of this type is called a horizontal return tubular
boiler or HRT. The next step was to use the
tank with a large tube and a number of smaller
ones. The fire was made in the large tube and
the gases made a number of passes through the
smaller tubes. This is the scotch marine type
boiler.
Fire Box Type
The "fire box" boiler is a further development of
the fire tube boiler. In this type the walls of the
furnace are made of flat steel having an internal
space connected to the tank. The gases flow from
the furnace through tubes then reverse and flow
through more tubes to the stack.
Water Tube Boiler
The next development was the straight tube boiler
with water inside the tubes where headers are
dropped from the drum and are connected with
straight tubes set on an angle. Another develop-
ment of the straight tube boiler was arranging
the tubes vertically between 2 drums or cylinders.
The bottom drum was the "mud" drum, the top
was the steam drum. These designs increased
the capacity obtainable from one unit.
Later Developments
Superheaters were added to heat the steam above
the boiling point.
The bent tube boiler was developed. It had sev-
eral drums connected with tubes bent in various
ways.
The water-cooled furnace appeared next. This
furnace is lined with tubes connected to the water
side of the boiler. They may be of many shapes
and lengths.
Through the years furnaces and superheaters
have increased in size, but the capacity of a
single unit has become much larger. Pressures
and temperatures have also increased.
Economizers are now used to increase the ab-
sorption of heat by the water. Air heaters of
various forms are used to increase the com-
bustion air temperature and increase the heat
used.
Boilers are now made to develop over 8,000,000
Ib of steam per hour at pressures at or above
critical steam pressure (critical pressure is
about 3, 200 Ib per square inch). Steam tem-
peratures have increased to about 1100°F.
Efficiency of use of coal has increased from
about 65% to 90%.
When boilers were first invented, an arbitrary
figure of one boiler horsepower for 10 sq ft of
heat surface was used. This figure is still used
with small boilers. By definition one b. h. p. is
equivalent to 34. 5 Ib of steam at 212°F contain-
ing 970.4 Btu per Ib or approximately 33,450
Btu. All larger water tube boilers are now rated
in Ib of steam per hour for maximum continuous
load. Small fire tube boilers should not be
required to produce more than one boiler horse-
power for 7 sq ft of heating surface. This pre-
vents excessive heat shock and damage caused
by expansion of parts.
The limits for large water tube boilers are
determined by the heat transfer per square foot
of exposed surface (whether exposed to radiant
heat or convection), the water circulation pat-
tern (natural of forced), the purity of the feed
water, the cleanliness of the wetted surfaces,
and the provisions for obtaining "dry" steam in
advance of the superheater.
Fans
The forced draft and induced draft fans are very
important in obtaining the specified capacities.
The forced draft fan should be designed to pro-
duce 25% more quantity of air than required for
peak operation and 20% more static pressure.
The induced draft fans should be designed for
15% more capacity than is required for peak
operation and 15% more static pressure.
Another way to state the required capacity is to
specify that all fans should be capable of supply-
ing sufficient air for the unit to develop full
peak load with 35% excess air. This is neces-
sary to provide for "pick-up" and peak load
capacity under less than optimum conditions or
high fuel-air ratios. B-33
-------
Design of Coal Combustion Equipment
Furnaces - Combustion Chambers
^
Furnaces vary in heat duty depending on size and
method of firing. The heat release rate for small
fire tube boilers, as well as in the smaller water
tube units, furnace height or flame travel is the
most important criteria of good furnace design
or stoker application. It should be emphasized
here that when the flame impinges on cold sur-
faces, smoke and soot are formed.
Some years ago the Stoker Manufacturers Associ-
ation developed a curve of minimum furnace
heights to be used with single retort stokers.
These data have often been used as the recom-
mended height. However, they frequently are
too short for good smoke-free operation and
good combustion. The curve labeled "B" in
Figure 1 is about 15% higher and does give good
results. Secondary air should always be pro-
vided. Sometimes with the smallest units (under
100 Ib per hour) slots in the furnace door will
provide the needed air.
The furnace heat release for units using multiple
retort stokers should be between 30,000 Btu/cu ft
and 40, 000 Btu/cu ft/hour depending on the size
of the equipment. High rear arches are some-
times used. These water-cooled arches, well
proportioned, promote mixing of lean gases at
the rear of the stoker with rich gases from the
front or upper end. Secondary air is seldom
needed, particularly if the furnace uses a water-
cooled arch.
Traveling Grates
Furnaces using traveling grate stokers should
have a heat release of between 30, 000 and
40, 000 Btu per cu ft per hour depending on size
and furnace design. Front and rear arches are
usually used. Secondary air should always be
used. It should be introduced through both the
front and rear arches. It may be as high as 25%
of the total air required.
Spreader Stokers
Furnaces for spreader stokers are usually "open"
with no arches. The heat release rate should be
between 25, 000 Btu/cu ft per hour and 35, 000
Btu/cu ft per hour depending on capacity and type
of grate. Secondary air is needed both at the
front wall and rear walls. Sometimes it is ap-
plied at the side walls. If adequately applied, it
will reduce particulate emission.
Vibrating Grate Stokers
Furnaces for the vibrating grate type stokers
usually have a very short arch at the front wall
and a longer arch, water cooled, at the rear.
B-34
The heat release is in the range of 30, 000
Btu/cu ft to 40, 000 Btu/cu ft per hour. High
velocity secondary air is needed at both the
front wall and the rear wall. It is often as high
as 25% of the total air required. This stoker
does not produce much fly ash except during the
frequent shaking of the grates.
Pulverized Coal Firing
Furnaces for pulverized coal firing are always
water cooled today. They may be of varying
shapes and configurations depending on the
manufacturer, the placement of burners, and
whether they are wet bottom or dry bottom fur-
naces. The heat releases are usually between
20, 000 Btu/cu ft and 30, 000 Btu/cu ft per hour.
Various methods of introducing secondary air
are used with this type of firing. This again,
depends upon the manufacturer and the type of
burner. Inasmuch as the coal is ground to a
very fine powder the ash particles are much
smaller; however, the amount of particulate
leaving the furnace is usually very high, although
it is somewhat less with the wet bottom type
furnace.
Cyclone Firing
With cyclone firing, the furnaces are in two
parts: (1) the cyclone itself where the heat re-
lease rate is very very high and (2) the main
furnace (it could be called a secondary furnace)
where the total heat release should approach
that of other suspension firing.
All present-day furnaces for water tube boilers
are water cooled to some degree. There are
considerable differences in the amount of water
cooling, the spacing of tubes, and other details
depending upon the duty expected from the unit,
the manufacturer, the type of firing, and the
coal characteristics.
Stacks
In times past many boiler plants have been built
with short steel stacks (stub stacks). These
stacks might not be over 25 feet above the top
of the roof of the power plant. In spite of any-
thing the operators could do, such plants were
not very good neighbors as both gases and par-
ticulates would be released relatively close to
the ground. It is my belief that no fuel-fired
boiler plant should be built today with short stub
stacks. The stack should be of sufficient dia-
meter so that the velocity of the gases will have
some effect on plume rise. The diameter should
not be so small that appreciable draft loss oc-
curs in the stack itself. The breechings or duct
work connecting the boiler equipment with the
-------
to
0)
.c
o
c
0)
I
0)
o
o
c
80
70
60
50
C-Recommended
40
30
20
-Stoker Mfgr.
Assoc. data
A - Not recommended
200
400
600
1400
1600
1800
800 1000 1200
Stoker Capacity, I'b coal/hr
FIGURE 1. SETTING HEIGHTS FOR FIRE BOX BOILERS WITH SINGLE RETORT STOKERS
2000
a
O
I
m
f
13
0)
-------
Design of Coal Combustion Equipment
stack should not be restrictive when related to
the gas velocity. Corners or change in direction
of such breechings should be rounded so that
minimum draft loss is required and so that full
use of the duct area will be obtained.
Coal Composition - Its Effect on Design
It is difficult to set exact limits on the effect of
coal composition and burning characteristics on
the design of firing equipment and furnaces.
Flame characteristics are considerably different
between suspension burning and fuel bed burning.
When fuel beds are used (stokers), the high
volatile coal (over 30% volatile) makes a long
opaque flame. This fact indicates that the flame
travel, which bears on the retention time, must
be long. This flame travel can be shortened by
the judicious use of secondary air jets. At the
other extreme, low volatile coal (20% to 25%
volatile) burning on fuel beds makes a shorter
transparent flame. A smaller furnace can be
used and there is less need for high velocity
secondary air jets. In this relation there should
be no flame impingement on any heat absorbing
surfaces. If there is such impingement, unburned
carbon will be formed from the cooling effect of
the tubes and black smoke will result.
There may also be the less obvious products of
incomplete combustion. The formation of sulfur
dioxide and its further conversion to SO-, and
sulfuric acid can cause considerable corrosion
problems in air heaters, breechings and dust
collectors if the temperature of the gases is re-
duced to a point close to the dew point. This
point of corrosion is not in itself a limiting
criteria. The metal temperature of equipment
adjacent to the flue gases is the critical item. If
this metal temperature is at or below the dew
point of either water or sulfuric acid, corrosion
arid plugging will occur.
Ash Content
Ash content is only important by itself in that
there must be sufficient ash to keep the grate
covered and well insulated from the heat when
fuel bed firing is used. The ash content of the
coal used with all stokers, except with very
small domestic units, should never be less than
5%. Most fuel bed type equipment (except the
small screw feed stokers) will operate satis-
factorily with very much higher ash content. The
ash softening temperature (AST) is not important
by itself, but only in connection with the ash con-
tent of the coal. In order to have good operation
and minimum maintenance, the ash content should
increase as the ash softening temperature
decreases. >
The only stokers that should use double screened
coal are those of the screw feed type and the
small ram-type single-retort stokers. These
stokers should use a top size not to exceed
1-1/4" and a bottom size not greater than 5/ 16".
Double screened coal is not normally used on
any of the larger fuel bed stokers. The top size
can vary up to 2" with industrial type stokers.
Under normal conditions the larger industrial
stokers will operate well with coal containing
40% that will go through a 1/4" screen. How-
ever, the particulate emission may indicate the
need for double screened coal with spreader
stokers. The top size should not exceed 1-1/4"
if it is des ined to be used with pulverized coal
firing unless the plant is equipped with a crusher
to reduce the top size to 1" or less. There have
been some traveling grate stokers and spreader-
stokers that have used very small sizes, such
as 1/2" x 0 slack with some success. Where
such small sizes are used on stokers, the dust
concentration in the furnace increases rapidly,
and the emission from the stack will increase.
These small sizes can be used quite satisfac-
torily with pulverized coal or cyclone firing.
Ash fusion temperature is quite important from
the standpoint of slagging effects in the furnace
and on the "screen tubes" when used with sus-
pension firing and dry bottom furnaces. Wet
bottom furnaces do not, of necessity, have a
lower limit of ash fusion temperature but an
upper limit must be observed.
Instruments
Instruments, gages, and control apparatus are
mandatory for good operation of any fuel firing
equipment. The minimum control can be used
with a small screw feed stoker or "domestic"
sizes, and up to the small commercial sizes.
This minimum control would consist of some
method of stack draft control (such as an auto-
matic "barometric" damper) and a start-stop
stoker control which may be actuated by air
temperature, steam temperature or water tem-
perature. There should be a safety shut-off
device to prevent overheating. If the stoker is
to operate a boiler, the boiler should have a
pressure relief valve. When the size of the
equipment is increased, more controls are
necessary to obtain optimum results.
The boiler controls used on the industrial type
boilers consist of the coal feed control, the
positioning type control which pre-sets the stack
dampers, and the control for the forced draft
fan dampers. The actuating medium will be the
steam pressure. If the size of the unit is in-
creased, the control apparatus should be of the
more accurate metering type which measures
air flow, gas flow, coal feed, and makes cor-
rections in accordance with load conditions and
a predetermined relationship between air re-
quired and fuel feed. Draft gages to indicate
various air and gas pressures of steam and feed
B-36
-------
Design of Coal Combustion Equipment
water and of flue gases are required. Flow
meters to determine steam flow and air flow
should also be used. They act as metering and
control devices so that optimum results may be
obtained. TV cameras and computers are often
used with still larger units to obtain quicker re-
sponse and more complete information.
Factors Affecting Air Pollution
At present, feasible methods of eliminating SC>2
from the flue gases of combustion apparatus are
still in the development stage. The sulfur diox-
ide can be dispersed by high stacks so that high
concentrations will not reach the ground level.
The amount of SO? produced is directly propor-
tional to the sulfur in the fuel with the minor ex-
ception that some sulfur will appear in the ash
pit and fly ash.
The quantity of nitrogen oxides (NOX) produced
largely depends on the furnace temperature and
retention time in the high temperature zone. The
theoretical flame temperature for coal burning is
in excess of 4000°F. The practical flame tem-
perature in the hot zone of any stoker or pulver-
ized coal flame will be of the order of 2800°F to
3000°F. This high temperature zone may be
small or quite large, depending on quantity of
fuel burned in a given time. The quantity of NO
formed will depend on the size of this high tem-
perature zone.
Particulate emission depends on many variables:
1. Type of Firing - least emission with
underfeed stokers to greatest with
pulverized coal.
2. Furnace Design - least emission with
large furnaces greatest with small
furnaces or pulverized coal. Arches
assist in reducing emission.
3. Secondary air jets tend to reduce
emission.
4. Coal Size - the greater proportion of
small sizes, the higher the emission.
5. Volatile Content - long flame or short
flame - pertains to pulverized coal
firing or stokers.
6. Degree of Coking - coke button FSI -
high coke button will produce higher
emission; very low coke button will
also produce higher emission.
7. Amount of Ash - the higher the ash,
the higher the emission.
8. Reinjection - reinjection makes for
high emission.
9. AST - the lower this temperature may
be, the smaller the quantity of fly ash
emitted.
Dust Collection Equipment
Dust or fly ash emissions from the stacks of coal
fired boilers has been a problem ever since coal
came into use. At first smoke and fly ash was
an indication that the shop was working and
therefore was considered a necessary nuisance.
Good furnace design, adequate controls, and use
of secondary air has largely corrected or can
correct the smoke problem.
The dust emission problem can also be corrected
by using various ideas and equipment. The use
of baffles and change in velocity and direction
will usually be adequate for very small units when
careful operating practices are used.
As units become larger and firing equipment is
used at higher duty, special equipment must be
used. This equipment may vary from rather
simple cyclonic separation to the combination of
multicyclone collectors and electrostatic col-
lectors, scrubbers or bag filters.
B-37 and B-38
-------
COAL BURNING - DESIGN PARAMETERS
U.B. Yeager*, P.E.
I INTRODUCTION - A FEW BASIC FACTS
A I think of the three "t's" as forming a
mathematical equation for any given unit
and for an operating condition of that
unit: f T(time) + f T(Temperature) + f
T(Turbulence) = C(constant). But turbu-
lence brings to mind a mixing of a mass
within a space or volume or distance
cubed (length^) and a degree of mixing
also involves time. Moreover, heat
transfer by conduction and convection
involve the first power of the temperatures
involved while radiant heat energy trans-
fer makes use of the fourth power of the
temperatures involved. Hence, f Tx(Time)
+ | Ty(Temperature) + f M(Mass) + f
D (Distance) = c( Constant).
To me the last equation points more
directly to the corresponding change that
must be made in one or more of the re-
maining functions after one of the other
functions has been changed.
B Another fact to bear in mind is that all
fuels or combustible materials regardless
of their form, whether gas, liquid or
solid are burned aus a gas. All combustion
is first of all a surface reaction.
But the surface must be active and avail-
able for reaction - and not simply a
potential surface. Consider, for example,
that a cube of coal one foot on each side
has 864 'square inches of surface. Break
up this cube into one inch cubes and the
1728 cubes now have 10368 square inches.
Broken down into 1/300 inch cubes and the
whole potential surface becomes 3, 110, 400
square, inches. But, if in use, the fine
coal particles were packed, the total
potential reactive surface in effect reverts
to the initial available surface. With
various stoker fired equipment, an attempt
is made by means of "Selective Application"
to control the size consist (physical make-
up by sizes) of the coal and to create a
D
maximum available effective surface by
means of fuel bed agitation resulting from
the stoker movement to fit the operating
needs.
For this reason gas is an ideal fuel. Gas
offers the greatest available reactive sur-
face per unit of mass and per unit of heat.
Oil, by its degree of atomization and its
temperature, as fired, has its liquid form
converted into tiny liquid droplets from
which it is readily converted into a vapor
or gaseous state. Coal, as shown, may
have its reactive surface immensely in-
creased by a control of particle size to
meet the conditions of its burning. This
is true whether the burning is done on
grates or fuel bed or by suspension burning.
From the foregoing discussion it can be
stated that any coal fired unit, from the
simple pot bellied stove on through to the
huge utility power units, is first of all a
gas producer. The basic principles in-
volved between any one of these units and
the conventional gas producers are the
same. The only difference is the element
of time between the zone or point of gas
production and the final combustion of the
gas. With the conventional gas producer
and the consumption of its gas, the
elements of time and space are more
apparent. The time involved may be the
matter of several seconds and the distance
between gasification and final combustion
may be many feet. With the household
stove, iron melting furnace or the power
unit, the time may be reduced to small
fractional parts of a second and the dis-
tance or the zones of the two reactions
approach being concurrent.
For the final of the few basic concepts of
combustion this statement is offered:
Primary air determines the rate of com-
bustion reaction and secondary air deter-
mines the efficiency of its reaction. This
is true whether the combustion takes place
*Engineering Consultant, Air Pollution Program,
Department of Health, Commonwealth of Kentucky.
PA. C.ce. 17. 7.66
B-39
-------
Coal Burning - Design Parameters
on grates or as individual particles in
suspension burning. It can be stated that
the thickness of the fuel bed does not con-
trol the burning rate. Rather, the thick-
ness controls the amount of carbon mono-
xide that will be produced by the passage
of the primary air through the fuel bed.
II COAL BURNING METHODS
A Handfiring
Eary types of handfiring coal made use of
four different firing methods:
1 Spreading or Scatter. This method
fired the coal lightly, evenly and often
over the entire fuel bed.
2 Spot. This method fired the coal
mainly over the areas where the coal
had been more completely burned. In
some respects it was a modification
of number one.
3 Strip. This method fired the coal in
alternate strips or areas, front to
back. This, too, was a modification
of number one. Each strip was fired
a little heavier at each cycle or firing
than was true of number one.
4 Coking. This method first cleaned off
part of the ash; the glowing fuel bed
was pushed back on the grates; and,
the fresh or green coal was fired at the
front. This method was considered
best to lessen smoke because the dis-
tilled volatile gases were carried back
and over the incandescent fuel bed.
Combustion efficiency likewise was
increased.
All methods of handfiring were of the
overfeed type. That is, immediately
over the grates is a covering of ash.
Then above the ash is the glowing fuel
bed. The green or fresh coal is fired
on top of this incandescent fuel bed.
Mechanical methods of firing coal were
initiated in the early 1800's. These
methods or stokers really came into
their own during the period of 1885 to
1900.
B Overfeed Stokers
Early stokers were simply mechanical
adaptations of handfiring. Two of these
stokers were the (1) Westinghouse (Roney)
and (2) Murphy "V" types. The firing
principle was much the same as the
"coking" method of handfiring. Later,
rotating or chain grates were built. These
fired the coal continuously at one end
and deposited the ash into a pit at the
opposite end. Refractory arches promoted
the ignition and efficiency of burning.
All of these overfeed units made use of
natural draft. Then capabilities as to
flexibility of load conditions and output
capacity were determined accordingly.
Some of the chain grate units were: (1)
Combustion Engineering (Green and Coxe);
(2) Babcock and Wilcox; (3) Riley Stoker
Co. (Harrington), and (4) Johnson and
Jennings (Stowe).
A later modification of the chain grate
was called the link grate traveling stoker.
Basically, this was a different arrange-
ment of the stoker linkage. These may
or may,not have been the first stokers to
make use of forced draft or underfire air
under positive pressure. Subsequently,
the air was divided into zones or areas
from front to back. This brought about a
more positive, more proper and more
complete combustion at the desired point.
Various makes of the overfeed stokers
had some limited expansion even up to the
late 1920's.
C Underfeed Stokers
The underfeed stokers especially of the
larger size were developed before 1900
and had rather large usage prior to World
War One and some limited acceptance
B-40
-------
Coal Burning - Design Parameters
through to the mid 1930's. These stokers
operated on the principle of feeding the
fresh or green coal from below the incan-
descent fuel bed. The ashes were pushed,
gradually, upwards and away from the top
of the fuel bed. An advantage of this type
of burning is that the volatile hydrocarbons
distilled from the green coal must pass
upwards through the glowing fuel bed where
they may be more readily consumed be-
fore leaving the combustion zone. With a
proper adjustment of the coal and the air
ratios, these stokers can fire with a
smokeless type of combustion. The larger
underfeed stokers made use of a ram or
reciprocating plunger type of coal feed.
They, also made use of forced draft. The
smaller underfeed stokers for domestic,
commercial, small institutional and small
industrial usage had worm or screw-type
coal feeds. These stokers all had one
retort.
These screw feed stokers were especially
active in application in the later 1920's to
the later 1940's. At one time well over
one hundred makes of small screw feed
stokers were on the market. Ram type
stokers were of the single and multiple
retort design with the latter reaching
twelve or more retorts. -The single re-
tort ram type stoker, normally, has side
ash dump grates. The multiple retort
units has end dump grates for periodic
dumping and for continuous discharge of
the ash and clinkers. With one exception
the smaller screw feed stokers required
that the ash periodically be lifted out
manually in clinker form. One make
known as "The Original Pocohontas"
had a mechanical type of ash removal as
an integral part of the stoker. Very few
of the single retort stokers had any type
of mechanical agitation for the fuel bed
to maintain porosity. As a result "coke
trees" become something of a problem in
many cases. The. good that was achieved
was the result of good coal application,
suitable burning characteristics and the
proper size consist combined with im-
proved firing techniques. The multiple
retort units with alternate plunger feed
action and in some cases stokers with a
controlled grate adjustment, for an un-
dulating movement of the fuel bed from
the furnace front towards the rear, did
maintain a more reactive or breathing
fuel bed. These units consequently were
able to produce very high rates of com-
bustion per square foot of grate area.
Some of the leading American Manufact-
urers of the large underfeed stokers
were: (1) Detroit Stoker Company; (2)
Westinghouse Electric Manufacturing
Company; (3) American Engineering Com-
pany (Taylor); (4) Combustion Engineer-
ing Company (Frederick, CE, and E);
(5) Riley Stoker Company (Jones); (6)
Auburn Foundry Company, and (7) Canton
Stoker Company. Some of the manufac-
turers of the smaller screw feed stokers
included: (1) Auburn Foundry Company;
(2) Brownell Company; (3) Canton Stoker
Company; (4) Eddy Stoker Company; (5)
Iron Fireman Manufacturing Company;
(6) Illinois Iron and Bolt Company; (7)
Fairbanks, Morse & Company; (8)
Steward - Warner Corporation; (9) Hoi-
comb and Hoke Manufacturing Company,
and (10) Will-Burt Company.
D Spreader Stoker
The spreader stoker was invented in the
early 1800's but had only a limited accep-
tance by the 1920's. Its growth accelerated
during the 1930's and its greatest accep-
tance came after World War II. This
growth likely was the result of changes in
industrial growth and coal mining methods.
The spreader stoker works on the princi-
ple of both suspension and grate burning.
In some respects it was patterned after
the spreading or scatter method of hand-
firing. The grates may be of many types:
fixed, dumping (power or hand), undulat-
ing, vibrating, reciprocating and rotating
(traveling). Feeding of the coal is done
mainly by rotors or revolving feeder
paddle wheels. The "throw" of these
feeders may be from six to approximately
twenty feet. Furnace turbulence and fly
ash carry-over both are increased as the
throw increases. One type feeds the coal
pneumatically to its feeder plate. Spreader
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Coal Burning - Design Parameters
stokers permit great flexibility as to load
changes and capacities by ready response.
These stokers permit a rather wide range
as to coal grade (quality) and types. Nor-
mally, a high volatile type of coal is pre-
ferred. The make of the stoker dictates
the upper limit as to the size that may be
used with best satisfaction. Generally,
coal preparations of 3/4 inch to 1 1/4
inch top size (round hole screen equiva-
lent) give most satisfactory results. The
coal preparation has a great bearing on the
performance of spreader stokers. If the
consist of the coal is too coarse, very
little suspension burning takes place and
the response of the unit to load conditions
is very sluggish. If the consist of the
coal is too fine, the firing at or near unit
rating may cause minor explosive pulsa-
tions in the furnace during each throw of
the coal feed. Under such a circumstance,
the grate burning is nil. The explosive
hazard is rather minor but the periodic
"puffs" cause excessive fly-ash carry-
over. Moreover, these puffs cause an
excessively dusty boiler room and more
attention must be given to maintain good
housekeeping. A proper Selective Appli-
cation determines a consist between the
two extremes depending upon the unit
design and load conditions.
Various American Manufacturers of
spreader stokers include: (1) Detroit
Stoker Company (Roto, Rotograte, CC,
Vibra Grate); (2) Combustion Engineering
Company (C-E); (3) Hoffman Combustion
Engineering Company (Firite); (4) Riley
Stoker Company; (5) William Bros.
Boiler and Manufacturing Company; (6)
Erie City Iron Works; (7) American Coal
Burner Company (Furnace Feeder); (8)
Iron Fireman Manufacturing Company
(Pneumatic), and (9) Standard Stoker
Company. Earlier, both Westinghouse
Electric Company and American Engineer-
ing Company made spreader stokers.
E Pulverized Coal Firing
The firing of pulverized coal was invented
about 1895. Prior to World War I it had
only limited acceptance, and that being in
metallurgical applications. The first
power plant facility designed especially
for pulverized coal was the Lakeside
Station of the Wisconsin Electric Company
in 1921. This plant made use of a storage
type operation. That is the coal was
crushed to suitable size, heat dried,
pulverized and then the pulverized particles
were carried pneumatically to overhead
storage bins or bunkers from which the
coal was fed to the furnaces. The great
success of this station brought about the
enthusiasm which resulted in the
phenomenal growth of pulverized coal
firing. In some respects this method
may be considered suspension firing in
its purest and best form.
When using high volatile coal, the particle
size of the coal, as fired, is about as
follows: 65 to 75 percent under 200 mesh;
80 to 88 percent under 100 mesh and no
more than 2 to 3 percent plus 60 mesh.
When firing low or medium volatile coals,
the particle size, as fired, is about: 78
to 85 per cent under 200 mesh; 90 to 96
percent under 100 mesh; and, no more
than 2 percent plus 60 mesh. Satisfactory
and successful firing is more a function
of a minimum of oversize than an exces-
sive amount of ultra fine particles. Coals
with ash contents above 8 percent will
likely increase maintenance because of
excessive erosion to pulverizing surfaces.
However, 8 percent is not limiting and
much coal with over 8 per cent ash has
been consumed. Free ash in the coal is
much more abrasive than is the coal
itself. Also, it will be found that the ex-
cessive ash increases erosion problems
with all equipment whose surfaces come
into contact with the combustion gases.
Manufacturers of pulverized coal fired
equipment include: (1) Babcock and Wil-
cox Company; (2) Combustion Engineer-
ing Company; (3) Riley Stoker Company;
(4) Foster Wheeler Corporation; (5)
Strong-Scott Manufacturing Company;
(6) Whiting Corporation; (7) Kennedy -
Van Saun Manufacturing and Engineering
Corporation; (8) Pennsylvania Crusher
Division, Bath Iron Works Corporation;
(9) Williams Patent Crusher and Pulveri-
zer Company, and (10) Sturtevant Mill
Company.
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Coal Burning - Design Parameters
Most pulverized coal fired installations
use the direct firing method. That is the
coal is fed directly from the pulverizer
mills to the burners at the furnace. There
are two basic classes of pulverized coal
fired furnaces: (1) The dry bottom fur-
naces, and (2) The wet bottom furnaces.
In the first class the furnace ash is re-
moved from the furnace in a solid dry
form. In the wet bottom or slag tap fur-
nace the ash is removed from the furnace
in molten form.
Surface moisture in the coal above 4 per
cent may cause problems in transporting
the coal to the pulverizer and an irregu-
lar flow of coal to the steam generating
unit. However, after the coal reaches the
pulverizer, the hot primary air from the
air preheater normally dries the coal
sufficiently to avoid further trouble. The
temperature of the coal and air mixture
at the burner is usually in the range of
150 to 170 degrees Fahrenheit.
F Cyclone Firing
The Cyclone Method of firing is a develop-
ment of the Babcock and Wilcox Company
and came into use shortly after World
War II. Firing coal with a cyclone type
burner is largely suspension burning
with some surface combustion from a
fluid fuel bed. A cyclone furnace consists
of a cylindrical, water-walled burner
about eight feet in diameter and about ten
to twelve feet long, set horizontally into
the wall of the primary furnace. One or
more cyclone units may be used per unit
depending upon the design and operating
needs. The particle size of the coal as
fired is all under 1/4 inch (round hole
equivalent). Coal received at the plant
of larger size should be crushed to the
proper burning size. It is felt that any
coal that can be handled and fed to the
burner can be burned. That is, the mois-
ture content as fired has less bearing up-
on a satisfactory performance than with
the previously discussed methods of
burning. Obviously, as the moisture con-
tent increases the "as-fired" heat content
per unit of mass must decrease. More-
over, there is a corresponding decrease
in the heat release both by unit input and
by heat loss by chilling as the moisture
is converted into superheated steam
within the furnace. It has been estimated
that about 80 to 85 per cent of the total
ash in the coal is discharged from the
cyclone and primary furnace in molten
form. The molten ash is chilled in a
stream of water causing pellets of slag
having a smooth, glazed, glass like par-
ticle, black or dark brown in color.
Because of the short time involved in this
type of burning, the temperature and
turbulence are both high. Heat release
within the cyclone ranges between 400, 000
and 700, 000 BTU per cubic foot per hour.
Ash content of the coal used is less cri-
tical than with pulverized coal firing be-
cause the coal particles are not reduced
to such a small size as fired. Coals
having an ash softening temperature of
1900 to 2400 degrees Fahrenheit are most
acceptable. Coals within the range of
2400 to 2600 degrees Fahrenheit for ash
softening temperature are marginal de-
pending upon the composition of the ash.
Few, if any coals having an ash softening
temperature above 2600 degrees Fahren-
heit are acceptable in current practice,
although, if the need were urgent enough,
proper design for their use could likely
be made.
Ill HEAT UTILIZATION
A furnace is a structural reaction chamber
wherein a combustion process can be initi-
ated or ignited, controlled and contained,
and the heat energy in another material.
Therefore, any furnace is simply a type of
heat exchanger. The use determines the
design and the design determines the results.
This is well shown in various iron foundries
where the purpose of the furnace is to melt
the iron or to maintain the iron already
molten at a suitable pouring temperature.
The furnace is so designed that the heat
B-43
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Coal Burning - Design Parameters
energy is reflected from the refractory
arches in such manner that the desired
temperatures are reached at a given point
or zone and this energy absorbed according
to the desired needs.
In steam generating units, the purpose is
to convert the heat energy of the fuel by
combustion into heat energy of the water
and steam. Within a steam generating unit,
the furnace proper, the boiler, the econo-
mizer, the superheater, and the air pre-
heater are all heat exchangers. All steam
generating units must have the first two
items just mentioned and they may have
none, all or any combination of the last
three items. Over the years there have
been many designs to accomplish that pur-
pose. To show something of the results
that have been accomplished, we might con-
sider the following:
Initially boilers were given a manufacturers'
rating by which ten square feet of heating
surface were considered equal to one boiler
horse power. A boiler horse power equals
the evaporation of 34. 5 pounds of water per
hour into steam at sea level (from and at 212
degrees Fahrenheit and one atmospheric
pressure). Since the latent heat of evapora-
tion equals 970. 3 BTU per pound of steam,
the total boiler horse power equals 33475
BTU. Or each square foot of heating surface
was supposed to transmit about 3348 BTU in
one hour. Now, it is estimated that the
direct radiant heat energy per square foot of
heating surface within a large modern power
unit is 70, 000 to 140, 000 BTU per square
foot per hour depending upon the cleanness
of the absorbing surface, with 80, 000 to
110, 000 BTU per square foot per hour as
being normal in practice.
Since the air preheater is the last heat re-
covery item in a power unit system, the
amount of heat remaining in the flue gases
at this point and available for recovery must
depend upon what recovery equipment has
been installed between the exit of the boiler
furnace proper and the preheater. The de-
sign of the air preheater will, also be in-
fluenced by the temperature at which it is
desired that the flue gases leave the preheater.
There are two basic types of air preheaters
depending upon the method of heat transfer:
(1) Recuperative and (2) Regenerative. To
some extent, the sulfur content of the coal
burned has a bearing upon the temperature
of the exit gases from the preheater: "It
is desired that the temperature be above the
dew point of the sulfurous and sulfuric acids
that might be condensed out of the flue gases. "
IV COMBUSTION CHAMBERS
Any thought of the act of burning must be
related to volume or the three dimensions.
A furnace simply gives fixed boundaries to
the act. Heat release is the amount of heat
liberated within a unit of volume in a unit of
time. Normally, heat release is stated as
"BTU per cubic foot per hour. " If the burn-
ing takes place on a stoker a combustion rate
may be used as "the weight of fuel burned
per square foot per hour". Due to variations
in the quantity of heat per unit weight the
above expression is not fully acceptable.
A more accurate definition is, "the heat re-
leased per square foot of grate surface per
hour" or "BTU per square foot per hour".
Different uses of the heat require different
rates of heat release. Consequently, the
furnace must be constructed in such manner
both as to design and materials as to achieve
that goal. For instance in the melting of
iron, the heat release must be quite high,
and the design of the walls and arches of
such refractory materials capable of with-
standing the heat and directing it to the
proper zone or area.
Power plant furnaces have been subject to a
wide variation in design and in materials of
construction. Now, there appears to be
more of a standard for the different types of
burning. Obviously, the individual require-
ments must determine the basic needs and
different people or groups have different
approaches to those needs.
In order to hold down construction costs,
many of the larger power units are built with
what is known as semi-outdoor design. Here
all of the major heat recovery equipment is
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Coal Burning - Design Parameters
well insulated against heat loss but has no
other protection from the elements except in
some cases, just a roof. Most industrial
power plants are of the enclosed type.
Possibly these are not so well insulated. At
least during bad weather such heat as may
be lost can apply towards the comfort of the
operators.
Some American Manufacturers of refractory
materials are:
1 American Refractories and Crucible
Company
2 Armstrong Cork Company
3 Babcock and Wilcox Company
4 Carborundum Company
5 Combustion Engineering Company
6 Philip Carey Manufacturing Company
7 Denver Fire Clay Company
8 Eagle-Picher Company
9 Green, A. P., Fire Brick Company
10 Johns-Manville
11 Kaiser Refractories Div., Kaiser
Aluminum & Chemical Corporation
12 Norton Company, Refractories Div.
13 Plibrico Company
14 Porter, H. K. & Son
15 Union Carbide Corporation
16 North American Refractories Company
17 Harbison-Walker Refractories
Company
18 Corhart Refractories Company
V DRAFT - NATURAL, FORCED AND
INDUCED
r
Draft is the resultant force that causes the
flow of gases in an enclosure and is brought
about by the differences in pressures at two
critical points. These differences in
pressure may be caused by temperature
difference of the gases within and without
the enclosure or may be caused mechanically.
In, general power plant use, one atmosphere
is the standard or base from which drafts
are measured. Negative and positive
pressures involved in drafts are measured
in inches of water because for the range in-
volved this is the most accurate method.
In normal power plant usage there are
three kinds of draft:
(1) Natural
(2) Forced
(3)Induced
In principle, both natural and induced drafts
are akin in that they both function from the
exhaust or discharge end of the furnace
system. Forced draft functions from the
opposite or feed end of the system.
Natural draft works on the principle of a
rising and expanding column of hot gases
leaving behind a negative pressure. This
causes fresh or primary air to be drawn
through the grates, into the fuel bed and on
through the furnace system to balance out
the pressure. Gases have no tensile strength,
no pulling power in themselves but by com-
pression they do have a pushing property.
The natural draft system is characterized
by simplicity and is dependent upon the tem-
peratures of the inside flue gases and the
outside air, upon the height and diameter of
the chimney and upon the velocity of the
gases moving within the chimney as well as
the resistance offered by the chimney,
breeching and other features to the flow of
the gases. Therefore, each such unit has
limitations as to capacity and flexibility of
operations.
B-45
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Coal Burning - Design Parameters
The forced draft fan supplies the primary
air for combustion. This may be by forcing
the air through the grates and into the fuel
bed. It may be the means of picking up the
coal in a pulverizer and bringing both the
pulverized coal and the air to the furnace.
As noted earlier, this system operates under
positive pressure. It is characterized by
increasing the flexibility and the output
capacity of the furnace system. Primary
air determines the rate of combustion. A
forced draft system and a natural draft
operate well together, for each assists the
other.
\
The extended use of heat recovery equipment
between the zone of combustion and the final
emission of the flue gases from the system
adds to the draft loss or in other words in-
creases the resistance to the flow of the
gases. Moreover, the equipment between
the furnace and the chimney is such that heat
transfer must be made by scrubbing action
of the gases with the heat transfer surfaces.
This equipment includes air preheaters,
economizers, boiler tubes, superheater tubes,
breeching, numerous baffles and dampers
and various equipment to lessen the emission
of solid particles from the flue gases. Under
such circumstances the induced draft fan
causes the unit to become more readily
responsive to load conditions. This is es-
pecially important for rapidly changing
process load operations. The induced draft
fan simply draws the hot gases from the
breeching or other related equipment and
forces them into and up the chimney. This
fan supplements both the forced draft and the
natural draft.
Since World War II, many industrial plants
having process loads, have installed induced
draft fans for use with the relatively short
steel venturi type smoke stacks.
VI CHIMNEYS AND BREECHING
A chimney or smoke stack is intended to
discharge the products of combustion into
the atmosphere. A chimney's effectiveness
is determined by: (1) the temperature of
the flue gases within and the temperature of
the surrounding air; (2) the height of the
chimney; (3) the cross sectional area; (4)
the shape of the cross section; (5) the velocity
of the hot flue gases; (6) the relative
humidity of the air, and (7) the materials
of construction. Any one of several chimneys
may satisfy the needs for a particular unit.
Since the relative costs of chimneys increase
with height, economy may dictate a shorter
chimney of larger diameter over a taller
chimney of smaller diameter.
The temperatures involved with the parti-
cular chimney determine to a great extent
the refractory needs both as to chemical
composition and the extent of the use of
special refractory to meet the conditions.
In general power plant use, the temperatures
of the flue gases may range from a low of
about 275 degrees Fahrenheit to possibly as
high as 750 degrees Fahrenheit with about 500
to 550 degrees Fahrenheit being a fair average
of flue gas temperature to the chimney.
Naturally the amount of heat recovery equip-
ment between the furnace and the chimney
will determine the specific temperature for
the specific units.
Initially the breeching was the connecting
link between the furnace and the chimney.
Currently one may expect to find one or more
of the following between the same two points:
(1) economizer; (2) air preheater; (3) fly
ash collector (mechanical and/or electrical),
and (4) induced draft fan. In effect, the
breeching thus becomes a series of short
duct work connectors. In some respects
the early breeching did serve as a modified
type of fly ash settling or collecting chamber.
As such and depending upon local conditions
they did need to be cleaned periodically.
The breeching may be circular or rectangu-
lar in cross section but its effective area
must be in keeping with the needs of the fur-
nace and the size of the chimney.
Gas velocities within the breeching and the
chimney will depend upon the unit design
and the operating conditions. The velocities
will vary but a velocity of 20 to 25 feet per
second has some degree of merit.
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Coal Burning - Design Parameters
VII ASH AND SULFUR IN COAL
A Ash
Ash in the coal is found in two types:
(1) Intrinsic or inherent ash which is
the mineral matter contained in the
original vegetation from solutions of
inorganic salts and possible later reaction
with the organic matter and from finery
divided particles as a suspended colloidal
mixture in the water in which the plant
life grew and decayed; and (2) The ex-
traneous ash which is the irregular in-
clusions of inorganic matter from layers
of varying thickness of very thin layers,
small fractions of an inch, up to many
feet in thickness of clay, shale, slate,
limestone and other inorganic materials.
The intrinsic ash is the mineral which
was absorbed by and deposited with the
plant life in such finely divided form as
to become a structural part of the coal.
It, therefore, cannot be separated from
the coal by the standard methods of
cleaning currently in use. The materials
1 forming the extraneous ash were deposited
. by floods or washed in with high water or
were the result of alternate elevations and
depressions of the earth's surface during
the periods of coal formation. Mining
methods themselves may be other means
of adding to the extraneous ash as pro-
duced for use. Much of the extraneous
ash may be removed from the coal after
mining by various methods of cleaning
based upon separation by selective
specific gravities.
Of course, one cannot give an accurate
figure, for as indicated above, the
amounts will vary between mines and even
at times within any one mine but for an
approximation, one might estimate that
for every six tons brought out of a mine,
one ton may be discarded as refuse by
suitable cleaning. The refuse may range
from as much as one in three tons to one
in sixteen tons mined.
Ash in the coal has many factors in its
utilization, most of which are adverse,
as follows:
1 Ash being a non-combustible, reduces
the available heat value by an amount
proportional to its content.
2 Ash increases the transportation and
handling costs of the coal.
3 Ash, especially the extraneous ash,
increases costs in mining and
preparation.
4 Ash particles in movement in the gas
stream of a furnace unit causes tube
and/or refractory erosion.
5 Finely divided ash particles emitted
from a furnace as fly ash increase
the problems of and cause a nuisance
in air pollution.
6 Ash lessens heat transfer by deposits
on heating surfaces as ash, slag or
clinkers.
7 Ash above a unit optimum lessens
unit efficiency.
8 Ash above a unit optimum increases
maintenance costs.
9 Ash above a unit optimum increases
unit outage.
10 Ash above a unit optimum materially
increases the costs of its deposition
at the using facility.
Of all coal burning equipment currently
in use or that used in the past only one
type, pulverized coal fired equipment,
could use coal without ash. Most grates
and stoker fired equipment, depending
upon the use and application, seem to
have a critical ash content below which
satisfactory unit performance cannot be
had without excessive outage and mainte-
nance. Or, each unit has an optimum
ash content for greatest and most favor-
able acceptance. Therefore, some ash
is not a complete evil in the application
of coal.
B Ash Removal System
There are two kinds of ash of concern
from power plant operations: (1) Fly
ash and (2) Bottom ash.
Fly ash is collected by several different
methods of separating the solid particles,
soot, etc., from the gases of combustion:
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Coal Burning - Design Parameters
B-48
1 Mechanical (Dry)
a Settling chambers (unit or series
arrangement)
b Centrifugal (single large or many
small)
c Baffle trap
d Filtration (Bag filters)
2 Electric Precipitators
3 Gas Scrubber (wet)
4 Sonic or Ultra-Sonic Waves
Mechanical separation is a function of
the physical characteristics of the fly ash
particles. In effect, the particles are
dropped from the gases in the settling
chambers because the expansion into the
chambers gives the slower-moving gas
less "carry-power. " Centrifugal force
and the inertia of the solid particles to
change direction as readily as the gases
makes the separation from centrifugal
and baffle units. The filtration simply
separates the solids from the gases be
cause the gases can pass through the
openings in the bag filters while most of
the solids can not.
The electrical precipitator functions on
the basis that the particles acquire static
charges when ionized by an electrostatic
field.
Gas scrubbers make use of the mass and
force of the relative movement of the
liquid and gas streams to each other com-
bined possibly with the surface tension
of the water or solution to wash the solids
from the gas.
The sonic or ultra-sonic system simply
filters the solids from the gases by wave
motion and the solids inertia characteris-
tics to movement.
The bottom ash is made of loose ash or
masses of clinker that are collected in
the bottom of the furnace by gravity or in
an ash pit at the bottom of the furnace
where the stoker movement has discharged
such solid material. Such ash generally
is moved to outside storage tanks or to
other final deposition locations as
follows:
1 Manually by wheelbarrow or other
wheeled cart
2 By one of the various types of conveyors
noted earlier
3 By pneumatic handling system
4 By hydraulic handling system
Some American manufacturers of ash
removal equipment are:
(1) Allen-Sherman-Hoff Company
(2) American Blower Corporation
(3)Buell Engineering Company Inc.
(4) Dracco Corporation
(5) Fly Ash Arrester Corporation
(6) Green Fuel Economizer Company
(7) Koppers Company, Inc.
(8) Aerodyne Development Company
(9) Pangborn Corporation
(10) Prat-Daniel Corporation
(11) Research Corporation
(12)Thermix Corporation
(13) Westinghouse Electric Corporation
(14) Western Precipitation Corporation
C Sulfur
Sulfur is found in coal in three forms:
(1) as an iron disulfide. FeS2« called
pyritic sulfur or iron pyrites in a golden
color in the form of very heavy balls or
lenses and in small flakes or crystals or
bands as partings. This sometimes is
called "Fools Gold". (2) organic sulfur
originating with and forming an inherent
part of the plant life that formed the coal.
(3) combined sulfur generally as a sulfate
with calcium or other mineral matter
and seen as a gypsum of white surface or
as veins in the coal. The sulfides may
have been formed from the organic sulfur
evolved as hydrogen sulfide during the
decay of the vegetable matter. Again the
sulfates may have been formed by oxida-
tion of the sulfides.
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Coal Burning - Design Parameters
Generally it is considered that the
presence of sulfur in the coal weakens its
potential usefulness and limits its applica-
tion as an industrial product for: (1) the
problems of spontaneous combustion in
storage are increased; (2) corrosion of
various kinds of equipment used in
handling the coal, in the combustion of
the coal and in the handling of the gaseous
and solid products of combustion are in-
creased; (3) slagging and clinkering
tendencies of the ash are increased; (4)
the presence of sulfur in the coke used in
various metallurgical purposes of the
iron and steel industry is detrimental to
these products and uses, and (5) the
combustion products from burning sulfur
have been found to produce adverse condi-
tions as an air pollutant.
A fair portion of the pyritic form of sulfur
may be removed from the coal during its
preparation for use. In general, it can
be said that the closer the particle size
of the coal approaches the particle size
of the pyritic flakes, the greater the
separation can be and the freer the finai
coal product is of sulfur. However, at
present no economical means is feasible
for the removal of any of the organic and
sulfate forms of sulfur from the coal prior
to its initial use.
It does not of necessity follow that all
poor coals are characterized by high
sulfur contents. But by and large, most
high sulfur coals are considered relatively
poor coals, even though for some certain
applications they may give a very satis-
factory performance. A contamination of
the atmosphere by sulfur dioxide has long
been considered to be a public health
problem and a nuisance. Whether in
dilute concentrations as in the normal flue
gas (0. 05 to 0. 3 per cent by volume) or
in heavier concentrations as in roaster
gases from smelter plants (5. 0 to 10 per
cent) sulfur dioxide is an undesirable
air pollutant. There is some variation in
opinion as to the total amount of sulfur
that appears as an oxide in the combustion
process and that which remains with the
solid residue. However, of that portion
that does appear in the flue gas as sulfur
dioxide two to five per cent will be oxidiz-
ed further to sulfur trioxide.
The use of the terms High Sulfur and Low
Sulfur is rather meaningless. That
which may be considered high by one
usage may be considered low by another.
The use made of the coal must of necessity
determine the limitations of such as may
be available for application. A. M. Wand-
less in an article "The Occurrence of
Sulfur in British Coals" gives the following
as a tabulation, which seems to make
some sense for general power-plant usage
as a base even though some slight modi-
fications might be desired for use here:
Under 1. 0 Per cent - Very low Sulfur
1. 1 to 1. 5 Per cent - Low Sulfur
1. 6 to 2. 5 Per cent - Medium Sulfur
2. 6 to 3. 5 Per cent - High Sulfur
Plus 3. 6 Per cent - Very High Sulfur
It must be obvious that the sulfur content
of the coal determines the maximum
amount of the sulfur oxides that can be
produced per unit weight of coal. Like-
wise, it must be kept in mind that part
of the sulfur remains with the solid re-
sidue. With any given amount of sulfur
in the fuel as a base, the relative
loadings of SC>2 in the atmosphere can be
expected to vary in almost direct ratio
with the relative ratio of another sulfur
content to that standard base.
The amount and concentration of sulfur
trioxide (803), which is of critical im-
portance, in the flue gases depends not
only upon the amount of sulfur in the
coal burned but upon other factors which
effect the dew point temperature.
The factors affecting the dew point
temperature include:
(l)The concentration of the 803 present
per unit volume of the flue gas.
B-49
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Coal Burning - Design Parameters
( 2) The concentration of water vapor
(HgO) present per unit volume of
the flue gas.
(3) The amount of excess air used in
the combustion process. Thus, the
excess air, by simple dilution, re-
duces the concentration of 303 and
water vapor. Again, the amount of
excess air and the conditions of com-
bustion may increase the quantity of
sulfur trioxide formed by increasing
the ratio of sulfur trioxide to sulfur
dioxide.
(4) The fly ash present tends to absorb
part of the sulfur trioxide. The
amount of absorption is variable de-
pending upon existing conditions of
the particular operations. However,
the fact that this provision is true,
points to the desirability of keeping
all surfaces as free of fly ash as
possible in order to lessen corrosion
problems.
(5) The flame temperature and other
conditions in the boiler furnace and
the auxiliary equipment may have a
great effect upon the ratio of SOg to
SO2 in the flue gases.
Even with coals of the same sulfur con-
tent the above items may cause a wide
variation in the ratio of SOo to SO2 by as
much as five times.
Under some conditions it may be felt that
the sulfur content is a little too high for
best performance. In order to lessen or
to prevent a dew point corrosive nuisance
with its related maintenance problems,
the flue gas temperatures may be elevated
by a proper control of excess air. In-
creasing the flue gas temperature 100 de-
grees Fahrenheit lowers the normal
power plant efficiency by 2. 5 to 3 per
cent. Usage itself must determine the
sulfur content of the coal that may be used
with satisfaction.
D Considerations to Minimize Air Pollution
There are several factors influencing the
selection of particulate control equipment
as follows:
1 Whether the plant is in use and is
being revamped to meet the needs or
whether the plant is in the design stage
of construction.
2 The method of burning.
3 The heat content of the coal.
4 The ash content of the coal.
5 The rate of burning or the rate of
operation.
6 The physical consist of the coal as
fired.
7 The capability of the operating per-
sonnel and their civic view point.
8 The good neighbor policy of manage-
ment and the importance to them of
their public image.
9 The location of the facility with respect
to the community at large.
In speaking of fly ash emission it should
be specified whether these are furnace
emission or unit emission. A great deal
of fly ash may be emitted from a furnace.
But a reasonably high portion of such
emission may be removed from the gas
stream in the various boiler passes, fly
ash collectors, air preheaters, econo-
mizers, breeching, induced draft fans
and in the stack. When the latter is true
the problem largely is internal within the
facility and even more so within the unit.
Operating costs, handling problems,
maintenance costs, erosion, corrosion,
unit outage, good housekeeping and unit
efficiency may all be problems of direct
concern within the plant with little or no
problem from the outside.
B-50
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Coal Burning - Design Parameters
If the emission is from the unit the
problem becomes one of the facility
relationship to its neighbors and to the
community as well as being a technical
problem.
Suspension firing brings with its use a
higher amount of furnace emission than
does bed or grate firing. The reasons
for this are obvious in that the particles
of coal as fired generally are (1) smaller
and (2) are introduced into the furnace
at several inches above the grates. Com-
bined with a higher turbulence of furnace
gases it is only natural that the gases
leaving the furnace have a higher capabi-
lity of carrying a relatively great amount
of entrained solid particles. Bed firing
on the other hand begins with the firing
of larger particles and the consist may
be relatively coarse. In fact, the whole
concept of a breathing, porous fuel bed
is that a suitably proportioned range of
particle sizes as fired, will give a maxi-
mum of desirable available reactive
surface. Therefore, with the bed firing
starting with coal of larger consist and
larger particles, and with these placed
on the stoker fuel bed prior to entering
the furnace in some cases, there is less
active fuel bed and furnace action. More-
over, bed firing was originated largely
for steady loads while suspension firing was
conceived largely for process or swinging
loads. It is granted that each type of equip-
ment can be used for the opposite type of
load. That is, with the recognized qualifi-
cations, suspension firing can be used with
steady loads and bed firing can be used for
swing loads. Under these reversed uses it
will be found that the emission functions
likewise are reversed. However, with bed
firing the furnace emission seldom, if ever,
reach the status of suspension firing and if
the emissions do reach this status it is more
or less the result of a temporary condition
brought on by some unusual circumstance.
Some types of burning equipment make
use of a certain amount of fly ash rein-
jection. With the conventional overfeed
and underfeed stokers this is no problem.
This practice has been used extensively
with spreader stokers. But reinjection
may be open to question in real useful-
ness. At most only the larger coarser
particles should be returned to the fur-
nace. Moreover, this ash should be re-
turned to the stoker by some gravity
system and not reinjected pneumatically.
In many cases, the net gain, especially
when returning all of the fly ash pneuma-
tically, has been much less than
anticipated. In most cases, practically
all of the fly ash with the possible excep-
tion of that collected in the initial fly ash
collector, could just as well be run
directly to the ash hopper. Whenever
fly ash is reinjected pneumatically, the
total fly ash from the unit eventually is
increased; and the furnace walls; boiler
tubes; superheater tubes; and economizer
tubes; air preheater surfaces, and
induced draft fan blades are all severly
eroded. Very often the reinjected fly
ash increases clinker and slag formation.
In the end the total costs very often ex-
ceed the gain.
B-51 and B-52
-------
COAL BURNING - GOOD OPERATIONAL PRACTICES
U. B. Yeager*
I Normal Temperature Range in Combustion
Chambers, Particulate Control Equipment,
Stack, Etc.
The theoretical flame temperature of a good
coal is on the order of 3500°F to 4000°F.
Possibly 80 percent of that temperature is
more normal in practice. Different conditions
of heat release vary according to the load
conditions. Moreover, the design of the
unit coupled with the relative amounts of
refractory and water wall heating surface
determine the temperatures within the com-
bustion zone. Temperatures immediately
adjacent to the water wall tube surface will
approximate the temperature of the water
within the tube while a few inches within the
furnace the temperature will be many
hundreds of degrees higher. Out toward the
center of the furnace or near the flame zone,
the temperatures may be 2600 to 2900°F.
Obviously, depending upon furnace design and
the path of the flame travel, there must be
zones at temperatures between the two ex-
tremes. It is desirable, when possible, to
have the combustion gases cooled to the
temperature of or slightly below the ash
softening temperature of the coal being burned
as they enter the first bank of tubes. If such
a condition is questionable early enough, the
tube spacing may be widened in the super-
heater and first bank of boiler tubes. Any
slag accumulation then will not be excessive
or may be removed without too much effort.
If the condition cannot be corrected early
enough and slag does become a problem it
may be necessary to operate at a reduced
rating or to use another coal having a higher
ash softening temperature.
Except for the relatively small percentage
of units so designed and in use with positive
furnace pressure most units operate with a
negative furnace pressure. This negative
pressure or furnace draft is adjusted
properly to bring about the greatest heat
recovery before the gases enter the chimney.
Again, this adjustment must depend upon the
furnace design, equipment used, operating
conditions and firing technique. If the furnace
is of an all refractory construction, a higher
condition of draft (read in inches H2O) should
be used than if the furnace has a water wall
construction. For instance in the first case,
if the stoker were an underfeed or overfeed
traveling grate or a spreader feed type the
overfire furnace draft at about the fuel bed
level should be 0. 08 to 0. 12 inches H2O, or
more, while if the same unit had water walls
the draft at the corresponding point might
be only 0. 00 to 0. 08 inches H2O.
A unit that is designed to operate at a nega-
tive pressure should do so. If not, then,
the flow of combustion gases, in effect,
become bottled and the furnace pressure will
become positive. Very often, within a very
short time (minutes) the heat within the fur-
nace can become excessive to the extent that
the stoker furnace walls or boiler itself may
be damaged even to the extent of causing a
shut-down. Also, under such a condition the
furnace atmosphere approaches or becomes
reducing in character which again hastens
slag and clinker formation.
Assuming that we have the gases leaving the
primary furnace without too much trouble,
the purpose of the rest of the heat recovery
equipment is to absorb and recover the
greatest amount of the sensible beat available
in the gases consistent with good operations
before they enter the chimney. Whether a
superheater is used depends upon the usage
of the steam and the temperature of the
steam needed. It may be found either im-
mediately before or after the first bank of
boiler tubes and possibly in both places.
Since the purpose of the boiler is to produce
steam or hot water, one of the best means
of assisting it to reach or maintain adequate
capacity is by heat recovery with an econo-
mizer. This is simply, a water preheater
*Engineering Consultant, Air Pollution Program, Department of Health, Commonwealth of
Kentucky.
PA.C.ce. 11. 5. 66
B-53
-------
Coal Burning - Good Operational Practices
gaining its heat from the flue gases that
might be lost or wasted otherwise. It is
considered, generally, that an economizer
will add two to eight percent (or an average
of about five percent) to the units efficiency.
The last heat recovery item within the system
is an air preheater. Because of the products
involved, flue gas and air, the temperatures
must be relatively low, in power plant usage
at least. For that reason and to make a
good recovery, these units will have a large
heat recovery surface. These units may add
two to five percent to the unit efficiency. It
is desired that the flue gases leave the pre-
heater at a temperature such that they are
above the dew point of the gases as they
enter the chimney. The nature of the opera-
tions and, especially, the sulfur content of
the coal influence the exit temperature. When
conditions require that the exhaust gases
must have the temperature increased by
100°F, a loss in efficiency of 2. 5 to 3 per-
cent occurs. Moreover, it is desired that
the preheated air be of such temperature
that when blended with whatever room or
cold air may be necessary, that the air
temperature at the point of ignition will be
proper for the equipment used. For pul-
verized coal fired units, the coal-air temper-
ature at the burner should be about 150 to
165°F as an average even though the air
may have left the preheater at 375 to 450°F.
For stoker fired units it appears that the
temperature of the air at the stoker generally
should be below 250°F for satisfactory
performance even though higher temperatures
may be used in some cases with satisfaction.
The following maintenance costs have been
noted for stokers using preheated air but
cannot be said to be universally acceptable:
Air Temperature
at Stoker °F
200
300
400
450
Maintenance Costs
(cents per ton coal)
3
6
14
23
however, of maintaining good will and a good
public relationship within the community
outside the plant site. They, also, may be
a means of lessening maintenance costs by
the removal of the erosive particles that
can damage the economizer, air preheater
induced draft fan, dampers, etc. Fly ash
collectors, normally, are placed between
the economizer and air preheater and between
the air preheater and induced draft fan or
chimney. In some cases, a fly ash collector
may be placed between the last pass of the
boiler and the economizer.
Since it has been shown that the range of
temperatures is fairly broad, the following
are listed as being an approximation:
Furnace (Burning Zone) 1900 to 2900°F
Leaving furnace and
entering first bank of
boiler or supertubes
Leaving boiler and
entering economizer
Leaving economizer and
entering air preheater
Leaving air preheater
and entering stack
1900 to 2600°F
450 to 750°F
350 to 550°F
250 to
350°F
Fly ash collectors (particulate control
equipment) are not considered as heat re-
covery equipment. They may be a means,
II EFFECT OF COMBUSTION AIR
If it were possible to get a perfect mixture
of the fuel with the air for combustion in
proper manner, in proper time and under
proper conditions of temperature no excess
air would be required. Unfortunately, up
until this time at least such an ideal cannot
be achieved. It is necessary, therefore, to
make use of such excess air as may be
required to reach the desired results. Only
such excess air should be used as is neces-
sary to complete the combustion process
and to maintain the unit in such a condition
as to assure maximum unit availability or
to lessen outage (period unit out of service);
and, to give maximum unit efficiency con-
sistent with lowest operating and maintenance
costs. Increasing the excess air beyond a
desirable optimum increases the flue gas
temperatures and lowers the efficiency.
B-54
-------
Coal Burning - Good Operational Practices
Lessening the excess air below a desirable
optimum may lessen the flue gas temperature
and lower the efficiency. For instance, it
may be possible to lower the excess air and
to raise the percentage of carbon dioxide in
the flue gas temperature. Thus the
efficiency should be increased. But due to
a lack of proper contact of the air with the
fuel the carbon monoxide might be increased.
Under many operating conditions an in-
crease in the carbon dioxide content by one
percent might increase the efficiency by
one fourth to one-half percent. An increase
though of carbon monoxide by one percent
might lower the efficiency by 4. 5 percent.
That which might start to be a gain might
end with a much greater net loss.
With a good adjustment of air to the coal
feed, the flame will be yellowish orange
in color with no black tips. It will appear
soft. And its luminosity will give a maximum
of radiant heat energy transfer. If the air
is increased the flame will become whiter
in color and will appear to be harder,
sharper and more erosive. Its radiant
heat energy will be lessened. If the air is
decreased too much the flame will appear
to be blacker and the flame will be lazy and
without life. Since a reducing atmosphere
is now well indicated, soot may be formed
and collect at some point in the system.
The smoke will be dark.
With a good air adjustment and proper
burning the smoke from the chimney should
be just a light haze, either light tan or
light gray in color.
HI NORMAL COMBUSTION AIR
REQUIREMENTS
Regardless of the type of fuel whether it be
a gas, liquid or solid, theoretically per-
fect combustion requires approximately
0. 75 pound of air per 1000 BTU. Over the
years, I have done work with many fuels
(primarily coal of many kinds and grades
but also with oil, natural gas, by-product
manufactured gas, retort gas, low tempera-
ture coal carbonization gas, water gas,
carbureted water gas, producer gas and
blast furnace gas). In attempting to find
some common denominator for the fuels I
determined the above fact many years ago.
Of course, there are some variations de-
pending upon the analyses of the fuels. Of
the very large number of analyses from
which determinations were made the range
of air requirement varied from about 0. 65
to 0. 85 pounds of air per 1000 BTU with the
overall average about 0. 75 pounds per 1000
BTU. I have wondered many times as to just
how close this range might have been if all
samples could have been taken and analyzed
with equal accuracy. Quite often it is not
realized that the taking of a good, fair sample
of any fuel is most important, and sometimes
rather difficult to do. The best of analyst
and the best of laboratory equipment and
technique are worthless if the sample is not
representative.
Now, in practice, excess air is used
normally in amounts of 10 to 40 percent.
Therefore, for a quick check of the air
requirements one may use one pound of air
per 1000 BTU. While not given as an
accurate figure it still has use of estimations.
One cubic foot of air at a temperature of
70°F weighs approximately 0. 075 pounds.
Therefore, for all practical purposes,
0. 75 pounds of air equal 10 cubic feet of
air, or a 1000 BTU of any fuel requires
10 cubic feet of air for perfect combus-
tion (no excess air). Therefore, 1 pound
of air would indicate about 1/3 excess air
would amount to about 13. 3 cubic feet.
An air adjustment resulting in a flue gas
analysis of 12. 5 to 14 percent carbon
dioxide when using coal, generally is very
satisfactory. A higher figure may cause
a smoke emission. Also, the tendency
for slag and clinker formations are
increased. A lower figure will result in
a lowered efficiency.
IV SOOT REMOVAL FROM HEAT
EXCHANGER EQUIPMENT
Soot itself is a volatile hydrocarbon that has
been distilled from the fuel bed but which
has been chilled and condensed by striking
B-55
-------
Coal Burning - Good Operational Practices
some cool surface before it has had the
opportunity to be burned. It is of such
character that it will retain some of the
solid residue that may come into contact
with it. It will burn under suitable condi-
tions as you have learned from the burning
of soot accumulations in your own furnace
or chimney.
A clean smooth heating surface is best for
proper heat transfer. The surface must
be clean on both sides. Here we are dealing
solely with the gaseous or fire side surface.
Soot, ash and slag are the three main forms
of solid that may accumulate on the heating
surface. The form involved is a function of
the completeness of burning; of the furnace
temperatures involved; and of the location of
the accumulation. Therefore, a periodic
cleaning of the heating surface is necessary.
Unit design and operating conditions deter-
mine the amount and kind of cleaning that
are necessary. Normally, steam jets
mounted on suitable equipment are directed
against the heating surfaces. This equip-
ment may be permanently mounted within
certain gas passes or may be mounted for
retractable operation. In some cases,
compressed air or steel bristled brushes
may be used. Again, in some cases various
chemicals may be added to the fuel bed
either alone or with the coal for cleaning.
Chemicals that may be used for treating the
coal usually are chloride salts of calcium,
sodium or zinc. Personally, I am inclined
to think that these chemicals may do more
harm than good over an extended period by
corrosive action at numerous critical points.
The surfaces of air preheaters and
economizers may be cleaned by the erosive
action of falling soot. And, in some cases
the heating surfaces may be sand blasted.
Some American manufacturers of soot-
removal equipment are:
A Bayer Company
B Diamond Power Specialty Corporation
C Hahn-Pitz Corporation
D Vulcan Soot Blower Division Continental
Foundry So. Machine Company.
V Importance of Proper Fuel Bed-Depth
And Complete Coverage of The Fuel Bed
The burning of coal in a bed on grates in-
volves bringing the air into contact with
coal particles. In their relative relation-
ship the coal particles are still and the air
is in movement about them. Since the
combustion reaction is a chemical reaction
the reactive components must be supplied
in a fixed relationship.
If the fuel bed is too thick, the depth may
offer excessive resistance to the flow of
air and sufficient air may not be able to
penetrate in an amount necessary to meet
the load conditions or even to sustain com-
bustion. If forced draft is available, an
excessive underfire air pressure might be
required. A blasting of the fuel bed can be
a means of increasing clinker formation with
its attendant problems. At any rate the fuel
bed would become uneven in depth and
coverage.
If the fuel bed is too thin, an excessive
amount of air could be drawn through the
fuel bed without taking place in the burning
reaction. Again, the unit output would be
lessened and the efficiency of the reaction
greatly decreased. The draft could be so
regulated that the reaction of the air
through the fuel bed could be more correct
and complete but it is possible then that
the heat output would not be sufficient to
meet the load conditions.
Obviously, the fuel bed must be completely
covered. If it were not, the primary or
underfire air would simply short circuit
through the areas of little or no resistance.
The furnace would be chilled and the combus-
tion process could be stopped. This is one
reason why the underfire air of the stokers
is divided into zones. By having such a
control of the air, that portion of the fuel
bed that needs the most air can have its
due amount. By the same token another
area of the stoker that needs less air can
have its requirements met equally well. In
effect the complete fuel bed gets its proper
distribution of air.
B-56
-------
Coal Burning - Good Operational Practices
VI COMBUSTION AIR DISTRIBUTION
As noted earlier, the primary air controls
the rate of combustion and the secondary
air controls the efficiency. When the firing
equipment is such that the stoker or other
means of firing cannot or does not supply
sufficient air to complete combustion then
overfire air may be necessary. If the over-
all amount of excess air is somewhat low
then as much as 20 to 25 percent may be
required as overfire air. However, if the
amount of excess air is sufficient but turbu-
lence is lacking then possibly only 2 percent
of the total air applied as jets under higher
pressure may be sufficient. Possibly, a
potential amount of 5 to 10 percent of the
total air supplied as overfire air would be
sufficient in most cases. The individual
requirements will determine the amount
necessary.
The burning equipment must furnish sufficient
secondary air to meet the requirements
initiated by the primary air. It is here that
the three "T's" of combustion enter into the
process. There must be sufficient tempera-
ture over an ample period of time with a
suitable mixing or turbulence to bring to-
gether the air and combustible gases.
VII COMBUSTION QUALITY CONTROL BY
OPERATION
It has been said that an operator has three
means of quality control for combustion:
1 Flue Gas Analysis
2 Visual Observation; and
3 Furnace instruments.
But I am going to add another
4 Experience and morale.
Actually, the first three are meaningless
without the latter.
A Flue Gas Analysis
These may involve spot tests or may be
the result of continuous analyses from
suitable instrumentation. The items
sought generally are amount of carbon
dioxide, oxygen and carbon monoxide.
As noted elsewhere, a higher carbon
dioxide is sought without the presence of
any carbon monoxide.
B Visual Observation
This might be called "Reading the Fire. "
At least, with experience, an operator
can look at the fire and determine from
the color and shape of the flame; the
contour and coverage of the flue bed, a
great deal as to the actual conditions
existing within the furnace. With suitable
experience, he can determine when the
coal feed should be increased or decreased;
whether the air adjustment should increase
or lessen the air supply; whether clinkers
likely exist on the grates under the fuel
bed; whether the furnace draft is too much
or not enough: and the action that he
should take if corrections are necessary.
C Furnace Instruments
These should be present in an amount
necessary to help the operator do a good
job and to determine with some degree of
accuracy just how efficiently the coal is
being burned for the use intended. They
should not be in excess of the requirements
and definitely not to the extent that the
collection of the data becomes a demanding
chore or that the amount of instrumentation
is beyond the capability of the plant personnel
to understand; to appreciate and to service
or to maintain adequately. An instrument
that does not indicate the conditions with some
degree of accuracy is worse than no instru-
ments at all.
D Experience and Morale
Combined with the three items noted
previously, experience and morale should
help the operator do a good job efficiently,
economically and safely. Proper training
as an integral part of experience should
bring about a firing technique suitable for
the needs.
B-57 and B-58
-------
TERMINOLOGY USED IN INCINERATOR TECHNOLOGY
(1)
I FOREWORD
The definitions given below apply to conven-
tional commercial, industrial, and municipal
waste-incineration practices, and do not
cover special applications of incineration;
nor do they cover special features of certain
types of incinerators, for example, catalytic
devices.
II DEFINITIONS
1 Auxiliary-fuel Firing Equipment
Equipment to supply additional heat, by
the combustion of an auxiliary fuel, for
the purpose of attaining temperatures
sufficiently high (a) to dry and ignite the
waste material, (b) to maintain ignition
thereof, and (c) to effect complete com-
bustion of combustible solids, vapors,
and gases.
2 Baffle
A refractory construction intended to
change the direction of flow of the pro-
ducts of combustion.
3 Breeching
The connection between the incinerator
and the stack.
4 Breeching By-pass
An arrangement of breeching and dampers
to permit the intermittent use of two or
more passages for products of combustion
to the stack or chimney.
5 Bridge-wall
A partition wall between chambers over
which pass the products of combustion.
6 Btu (British Thermal Unit)
The quantity of heat required to increase
the temperature of one pound of water
from 60° to 61°F.
PA.C.ce.4. 1.66
7 Burners
Primary: A burner installed in the pri-
mary combustion chamber to dry out and
ignite the material to be burned.
Secondary: A burner installed in the
secondary combustion chamber to main-
tain a minimum tempe.rature of about
1400°F. It may also be considered as
an after-burner.
After-burner: A burner located so that
the combustion gases are made to pass
through its flame in order to remove
smoke and odors. It may be attached to,
or be separated from the incinerator
proper.
8 Burning Area
The horizontal projected area of grate,
hearth, or combination thereof on which
burning takes place.
9 Burning Rate
The amount of waste consumed, usually
expressed as pounds per hour per square
foot of burning area, Occasionally ex-
pressed as Btu per hour per square foot
of burning area, which refers to the heat
liberated by combustion of the waste.
10 Capacity
The amount of a specified type or types
of waste consumed in pounds per hour.
Also may be expressed as heat liberated,
Btu per hour, based upon the heat of
combustion of the waste.
11 Checker-work
Multiple openings above ^he bridge-wall,
and/or below the drop arch, to promote
turbulent mixing of the products of combustion.
12 Chute, charging
A pipe or duct through which wastes
are conveyed from above to the primary
B-59
-------
Terminology Used in Incinerator Technology
chamber, or to storage facilities pre-
paratory to burning.
13 Combustion Air
Primary: Air introduced to the primary
chamber through the fuel bed by natural,
induced, or forced draft.
Secondary: Air introduced above or be-
yond the fuel bed by natural, induced, or
forced draft. It is generally referred to
as overfire air if supplied above the fuel
bed through the side walls and/or the
bridge-wall of the primary chamber.
Theoretical: Air, calculated from the
chemical composition of waste, required
to burn the waste completely without
excess air. Also designated as Stoichio-
metric air.
Excess: Air supplied in excess of theoret-
ical air, usually expressed as a percentage
of the theoretical air.
14 Combustion Chamber
Primary: Chamber where ignition and
burning of the waste occur.
Secondary: Chamber where combustible
solids, vapors, and gases from the pri-
mary chamber are burned and settling
of fly ash takes place.
15 Curtain Wall or Drop Arch
A refractory construction or baffle which
serves to deflect gases in a downward
direction.
16 Damper
A manual or automatic device used to
regulate the rate of flow of gases through
the incinerator.
Barometric: A pivoted, balanced plate,
normally installed in the breeching, and
actuated by the draft.
Guillotine: An adjustable plate normally
installed vertically in the breeching,
counterbalanced for easier operation,
and operated manually or automatically.
Butterfly: An adjustable, pivoted, plate
normally installed in the breeching.
Sliding: An adjustable plate normally
installed horizontally or vertically in
the breeching.
17 Draft
The pressure difference between the in-
cinerator, or any component part, and
the atmosphere, which causes the pro-
ducts of combustion to flow from the
incinerator to the atmosphere.
Natural: The negative pressure created
by the difference in density between the
hot flue gases and the atmosphere.
Induced: The negative pressure created
by the action of a fan, blower, or ejector,
which is located between the incinerator
and the stack.
Forced: The positive pressure created
by the action of a fan or blower, which
supplies the primary or secondary air.
18 Flue Gas Washer or Scrubber
Equipment for removing fly ash and other
objectionable materials from the products
of combustion by means of sprays, wet
baffles, etc. Also reduces excessive
temperatures of effluent.
19 Fly Ash
All solids including ash, charred paper,
cinders, dust, soot, or other partially
incinerated matter, carried in the pro-
ducts of combustion.
20 Fly Ash Collector
Equipment for removing fly ash from
the products of combustion.
21 Grate
A surface with suitable openings, to
support the fuel bed and permit .passage
B-60
-------
Terminology Used in Incinerator Technology
of air through the fuel. It is located in
the primary combustion chamber and is
designed to permit the removal of the
unburned residue. It may be horizontal
or inclined, stationary or movable, and
operated manually or automatically.
22 Hearth
Cold drying: A surface upon which wet
waste material is placed to dry prior to
burning by the actual hot combustion gases
passing only over the wet material.
Hot drying: A surface upon which wet
material is placed to dry by the action of
hot combustion gases that pass successively
over the wet material and under the hearth.
23 Heat of Combustion
The amount of heat, usually expressed as
Btu per pound of as-fired or dry waste,
liberated by combustion at a reference
temperature of 68°F. With reference to
auxiliary gas it is expressed as Btu per
standard cubic foot, and to auxiliary oil
as Btu per pound or gallon.
24 Heat Release Rate
The amount of heat liberated in the pri-
mary combustion chamber, usually ex-
pressed as Btu per hour per cubic foot.
25 Heating Value
Same as heat of combustion.
ignited and burned, the solid residues of
which contain little or no combustible
material. (See Classification of
Incinerators.)
27 Incinerator, multiple chamber
An incinerator consisting of two or more
refractory-lined chambers, interconnected
by gas passage ports or ducts and designed
in such manner as to provide for complete
combustion of the material to be burned.
Depending upon the arrangement of the
chambers, multiple-chamber incinerators
are designated as in-line or retort types.
28 Settling Chamber
Chamber designed to reduce the velocity
of the gases in order to permit the settling
out of fly ash. It may be either part of,
adjacent to, or external to the incinerator.
29 Spark Arrester
A screen-like device located on top of
the stack or chimney, to prevent incan-
descent material above a given size from
being expelled to the atmosphere.
30 Stack or Chimney
A vertical passage whether of refractory,
brick, tile, concrete, metal or other
material or a combination of any of these
materials for conducting products of
combustion to the atmosphere.
26 Incinerator
Equipment in which solid, semi-solid,
liquid or gaseous combustible wastes are
REFERENCE
1 APCA publication, Vol. 15, No. 3, pp
125-126. March, 1965.
B-61
-------
00
en
to
CLASSIFICATION OF WASTE TO BE INCINERATED
(Incinerator Institute of America)
Classification of Wastes
Type Description
*0 Trash
*1 Rubbish
*2 Refuse
*3 Garbage
4 Animal
solids and
organic
wastes
Principal Components
Highly combustible
waste, paper, wood.
cardboard cartons,
including up to 10%
treated papers.
plastic or rubber
scraps; commercial
and industrial
sources
Combustible waste.
paper, cartons, rags,
wood scraps, combus-
tible floor sweepings;
domestic commercial.
and industrial sources
Rubbish and garbage;
residential sources
Animal and vegetable
wastes, restaurants.
hotels, markets;
institutional.
commercial, and
club sources
Carcasses, organs.
solid organic wastes;
hospital, laboratory.
abattoirs, animal
pounds, and similar
sources
5 Gaseous, Industrial
liquid or iprocess wastes
semi- liquid ;
wastes |
6 Semi- solid
and solid
wastes
Combustibles requiring
hearth, retort, or grate
burning equipment
Approximate
Composition
% by Weight
Trash 100%
Rubbish 80%
Garbage 20%
Rubbish 50%
Garbage 50%
Garbage 65%
Rubbish 35%
100% Animal
and H'ima::.
Tissue
Variable
Variable
Moisture
Content
%
10%
25%
50%
70%
85%
Dependent
on pre-
dominant
components
Dependent
on pre-
dominant
components
B. T. U.
Incombus- !Value/lb.
tible jof Refuse
Solids % ias fired
5% 8500
i
i
i
10%
7%
6500
4300
5% J2500
i
5%
Variable
accord-
ing to
wastes
survey
Variable
accord-
ing to
wastes
survey
1000
B. T. U.
of Aux. Fuel
Per Ib.
of Waste
to be
included in
Combustion
Calculations
0
0
0
1500
3000
!
Variable
accord-
ing to
wastes
survey
Variable
according
to wastes
survey
Variable
according
to wastes
survey
Variable
according
to wastes
survey
Re commended
Min. B. T. U. /hr,
Burner Input
per Ib.
Waste
0
0
1500
3000
8000
(5000 Primary)
(3000 Secondary)
Variable
according
to wastes
survey
Variable
according
to wastes
survey
*The above figures on moisture content, ash, and B. T. U. as fired have been determined by analysis of many samples. They are
recommended for use in computing heat release, burning rate, velocity, and other details of incinerator designs. Any design based on
these calculations can accommodate minor variations.
H
to
>-i
3
9
a.
3
o
I
H
n>
8-
-------
CLASSIFICATION OF INCINERATORS
(Incinerator Institute of America)
Class I - Portable, packaged, completely
assembled, direct fed incinerators having
not over 5 cu. ft. storage capacity, or 25 Ibs.
per hour burning rate, suitable for Type 2
Waste.
Class IA - Portable, packaged or job
assembled, direct fed incinerators 5 cu. ft.
to 15 cu. ft. primary chamber volume; or a
burning rate of 25 Ibs. per hour up to, but
not including, 100 Ibs per hour of Type O,
Type I, or Type 2 Waste; or a burning rate
of 25 Ibs per hour up to, but not including,
75 Ibs. per hour of Type 3 Waste.
Class II - Flue-fed, single chamber incinera-
tors with more than 2 sq. ft. burning area,
suitable for Type 2 Waste. This type of
incinerator is served by one vertical flue
functioning both as a chute for charging
waste and to carry the products of combustion
to atmosphere. This type of incinerator
installed, in apartment houses or multiple
dwellings not more than five stories high.
Class IIA - Chute-fed multiple chamber
incinerators, with more than 2 sq. ft. burn-
ing area, suitable for Type 1 or Type 2
Waste. (Not recommeded for industrial
wastes). This type of incinerator is served
by a vertical chute for charging wastes from
two or more floors above the incinerator
and a separate flue for carrying the products
of combustion to atmosphere.
Class III - Direct fed incinerators with a
burning rate of 100 Ibs. per hour and over,
suitable for Type 0, Type 1 or Type 2
Waste.
Class IV - Direct fed incinerators with a
burning rate of 75 Ibs.per hour or over,
suitable for Type 3 Waste.
Class V - Municipal incinerators suitable
for Type 0, Type 1, Type 2, or Type 3
Wastes, or a combination of all four wastes,
and are rated in tons per hour or tons per
24 hours.
Class VI - Crematory and pathological
incinerators, suitable for Type 4 Waste.
Class VII - Incinerators designed for
specific by-product wastes, Type 5 or
Type 6.
PA. C.ce. 33.9.66
B-63 and B-64
-------
DESIGN PARAMETERS FOR 1.1. A. INCINERATOR CLASSES
IIA, III, IV, VI AND VII
R. Coder*
I INTRODUCTION
In a discussion of Design Parameters, it is
advisable first to settle upon nomenclature
and definitions. Accordingly, we show here
a section through a typical Incinerator
(Figure 1) with most widely used terms.
These terms also correspond to those used
in Incinerator Institute of America 1963
Standards which will be the principle refer-
ence work for this subject.
II PRIMARY CHAMBER
This is the chamber into which refuse is
charged and which contains the grate and
hearth surfaces on which combustion is
initiated. Its function, therefore, is to
initiate combustion, provide for separation
of ash from combustibles, provide some
degree of refuse storage, and means for
combustion air admission and regulation.
An auxiliary burner is often added to provide
heat for reluctant combustible waste.
fer.ni.ITic Domp.r
Atfcpit Ooon St.p GFOHI
Figure 1. Incinerator Nomenclature
X
It is also important to note that there is no
single set of Design Parameters. The de-
sign parameters of the Incinerator industry
as per 1.1. A. Incinerator Standards are
used here together with those of the Los
Angeles County Air Pollution Control Dis-
trict. We feel that there is basically no con-
flict here but such differences that exist
will be shown and briefly discussed.
Only Class IIA, III, IV, VI and VII Incinera-
tors as defined in 1.1. A. Standards will be
discussed. They are all multi-chamber
incinerators.
*President, Joseph Goder Incinerators, Elk Grove
Village, Illinois. (Prepared February, 1966).
PA. C.ce. 18. 7.66
A Volume
The volume is determined by the designer
but according to 1.1. A. must not be more
than 60% of total Incinerator combustion
volume. L. A. parameters do not have a
specific value although by their grate area
and arch height stipulations, a volume is
rather closely determined and generally
agrees with 1.1. A.
B Grate Area:
The burning rate on the grate in an incin-
erator varies according to size of the
incinerator or grate loading and according
to type of waste. 1.1. A. Standards contain
a chart and formula. L.A. shows a curve
according to the following equation:
R_(lb. /hr.)
LG(lb. /hr. /ft.
= ft.
Where AQ is the grate area, RQ the
incinerator capacity and LQ the burning
rate on the grate.
The differences, if any, between the two
are minor since virtually the same curve
is used.
B-65
-------
Design Parameters for 1.1. A. Incinerator Classes
C Arch Height
L.A. provides a formula as follows:
HA= 4/3(AG)4/11 = ft.
1.1. A. does not consider this equation
applicable because of practical problems
and insufficient field and laboratory data
to show the validity of the equation. On
a 50 pound per hour incinerator, one
charge of an ordinary cardboard carton
would upset the theoretical relation.
D Length-to-Width Ratio:
L.A. has a recommendation as follows:
1 Retort Model: up to 500 Ibs per hr.,
2:1 ratio
over 500 Ibs per hr.,
1. 75:1 ratio
2 In-Line Model:
1. 6:1 ratio for 750 Ibs
per hr. to about 1:1
ratio for 4000 Ibs. per
hr.
Although 1.1. A. has no specification for
this relationship, the L. A. ratio is con-
sidered desirable where space limitations
permit.
in SECONDARY CHAMBER
The function of the secondary chamber is to
complete combustion and to collect ash
carried over from the primary chamber.
Effective means of completing combustion
are baffling and checkerwork to break
stratification, air ports to- supply combustion
air, large volume to equalize temperature
variations introduced in primary chamber
and to settle fly ash.
1.1. A.: A baffle to form a "down-pass" and
a velocity not exceeding 9 feet per
second with gas volume at 140QOF.
Also, limitations on length of gas
travel.
L.A. Specifies a maximum gas velocity.
Generally, a zone of low-gas velocity
is required and a change in direction
to effect "throw-out" of particles.
IV GEOMETRIC CONFIGURATION
This refers to the placement of the secondary
combustion chamber in relation to the
primary combustion chamber.
IN-LINE is that arrangement where
secondary chamber is at the rear of primary
chamber. See Figures 3 and 4.
RETORT is that configuration in which
secondary chamber is at the side of primary
chamber. See Figure 2.
SUPERIMPOSED is a more recent configura-
tion designe'd to save floor space in which
secondary chamber is superimposed on
primary chamber.
V AUXILIARY FUEL BURNERS
Auxiliary fuel serves two basic purposes,
namely, to supply heat to a waste that will
not support combustion such as wet garbage,
and to insure ignition of products of com-
bustion, via an afterburner. 1.1. A. pre-
scribes minimum size burners that shall
Figure 2. Retort Design Incinerator
B-66
-------
Design Parameters for 1.1. A. Incinerator Classes
Table 1. 1.1. A. Recommended Auxiliary
Fuel Burner Size(s)
Figure 3. In-Line Design Incinerator
Figure 4. In-Line Design Incinerator
be used in (Table 1) but does not specify
where it shall be admitted except in the case
of Class VI Incinerators. Note, that burner
input actually means burner size and actual
input is expected to average less than
burner capacity or input. 1.1. A. also
specifies that flame failure protection be
provided. Local regulations may be more
specific on flame failure protection.
Waste Waste
Type Description
Recommended Mini-
mun Btu/hr. Burner
Input/Ib of Waste
1
2
3
4
Rubbish
Refuse
Garbage
Animal Solids
and Organic
Wastes
1500
3000
8000
(5000 Primary)
(3000 Secondary)
Gaseous, Liquid Variable according
or Semi-Liquid to wastes survey
Wastes
Semi-Solid
and Solid
Wastes
Variable according
to wastes survey
VI DRAFT
Draft is the difference in air and flue gas
pressures and is usually negative relative
to the incinerator room atmosphere so air
will flow into and through the incinerator
to the chimney either by gravity or by means
of a fan in the breeching. In this latter in-
stance, it is called "induced draft. "
Draft is also required to draw air through
the grates and fuel bed. This may be
accomplished by gravity or by a blower. In
the latter case, it is called "forced draft. "
VII BREECHING & STACK
It is very important to realize that the gases
leaving an incinerator may be as high as
1800°F and they cannot be handled in the
same manner as boiler flue gases which
rarely exceed 600°F. This indicates the
necessity for adequate breeching and
chimney linings. Velocity of the incinerator
flue gases is not really important although
1.1. A. specifies a maximum velocity of 30
feet per second in the breeching.
B-67 and B-68
-------
OPERATION PRACTICES FOR 1.1. A. INCINERATOR
CLASSES IA, IIA, III, IV AND VII
R. Coder*
I INTRODUCTION
The ideal situation is one in which primary
chamber is cold and secondary chamber is
red-hot. The most practical situation is one
in which a waste hopper can be kept filled.
If exactly the right amount of air were ad-
mitted with no smoking at the doors or air
ports, the draft is perfect. 1.1. A. Standards
require the manufacturer to furnish a name
plate showing model, rating and waste type
to be incinerated. Also, required is a
written operating instruction. Work from
this sheet.
II CHARGING
All of the following factors must be considered
as related to each other:
A Loading vs Temperature
1 On cold start, feed non-smoky material
slowly and increase frequency -- not
size --of charge until secondary
chamber brickwork is a cherry red or
about 1250°F.
2 Where smoke is a problem, load
charging opening to keep it practically
blocked with waste.
3 Do not continue charging beyond point
at which incinerator brickwork turns
light pink or about 1600°F. Oxides of
nitrogen seem to form more readily at
higher temperatures.
B Mixing Charges
11 is often a great advantage to mix slow
burning material with flash burning waste.
This can be done to achieve more efficient
incineration of wet garbage or it can be
done to reduce smoke by mixing smoky
materials, such as plastics and rubber,
with paper waste.
Ill DRAFT
Control of draft is a relatively critical item
in operation. There is no one proper value
because the setting depends on the furnace
design. An overfire draft setting of
approximately 0. 05 inch water column seems
to be the most reasonable value if this
measurement is taken with incinerator
operating at rated capacity and with charging
opening closed.
1.1. A. specs require both a positive type
damper such as guillotine damper and a
barometric damper. The positive damper
can be considered as the rough setting and
the barometric as the fine setting. The
positive damper also should be completely
closed when cleaning the incinerator.
Excessive fly-ash is usually the result of too
great a draft. Frequently, operators open
the damper wide to permit higher burning
rate.
IV AIR ADMISSION
Basically, underfire air which is air admitted
under the grates causes a flyash problem be-
cause of the velocity of the air through the
fuel bed. Start with air under the grates al-
most closed and increase only enough to
bring incinerator to rated capacity. L. A.
specs detail size of air ports which more or
less proportions the air admission.
1.1. A. does not specify air ports and leaves
this item to manufacturers' designs since
there does not seem to be any well established
proportional distribution.
V STOKING
This was somewhat explained under "charging"
but it should be noted that ash must be sifted
through grates by manipulating moveable
grates or stirring fuel bed on stationary grates.
The latter creates considerable nuisance.
*President, Joseph Coder Incinerators, Elk Grove Village, Illinois.
PA.C.ce. 19. 7. 66
B-69
-------
Operation Practices
Ash removal is frequently neglected and a
heavy accumulation of ash on the grates
changes the design values radically.
Ash removal in the secondary chamber is
even more neglected. It is significant that
large quantities of ash£lo settle in the
secondary chamber although only to a cer-
tain depth after which the "settling" effect
of the chamber is lost.
VI COMBUSTION QUALITY CONTROL
In this group of classifications, at least on
incinerators under 1000 pounds per hour, the
operator's interest is generally poor. A
draft gauge of the direct reading type with a
mark on the face showing top limit should
be provided as well as a series of observation
ports to indicate temperature in the incinerator
and to show probable smoke density.
An indicating pyrometer, motorized damper
with draft indicator and smoke density indi-
cator would be an effective group of control
instruments on incinerators of 500 pounds
per hour or over.
VII SECONDARY BURNER
Where the incinerator is equipped with a
secondary burner, the procedure would be
to switch on the burner at start of firing for
about a one hour period and then for about
10 minutes at each charge.
Control by pyrometer is very difficult where
firing is not heavy and continuous.
A secondary burner may also be controlled
by smoke density indicator if time delay is
incorporated in the circuit.
VIII AIR JETS
These are effective where the incinerator is
fired heavily with smoky type wastes.
Class IA Incinerators are ordinarily supplied
with a complete set of operating instructions
by the manufacturer.
Class IIA Incinerators are operated very
much in the same manner as outlined here
for Class III, IV and VII Incinerators except
that all waste should be charged through
the intake doors at the several floors in the
building and not in the primary chamber
stoking or access door.
B-70
-------
FLARE COMBUSTION
Leonardo. Mandell, P.E.*
I INTRODUCTION
"Flare Combustion" is a highly-specialized
type of unsteady state, exposed-flame-
burning into the free atmosphere.
It has been developed mainly by and for the
Petroleum Industry. Flares provide a means
of safe disposal whenever it is impractical
to recover large and/or rapid releases of
combustible or toxic gases/vapors. These
releases may occur under emergency con-
ditions resulting from power or compressor
failures, fires or other equipment break-
downs; or under day-to-day routine conditions
of equipment purging, maintenance and
repair, pressure-relieving and other un-
wanted accumulations such disposal
being compatible with the public health and
welfare. Flaring has become more of a
safety or emergency 'measure. Combustible
releases with heat contents as high as
4, 000, 000, 000 Btu/Hr. have been
successfully flared.
Flares must burn without smoke, without
excessive noise, or radiant heat. They
should have a wide capacity to handle vary-
ing gas-rates and Btu contents. Positive
pilot ignition and good flame stability during
adverse weather conditions are also
necessary.
Typical gases that can be successfully flared
range from the simple hydrocarbon alkanes
through the olefins, acetylenes, aromatics,
napthenes, as well as such inorganic gases
as anhydrous ammonia, carbon monoxide,
hydrogen, and hydrogen sulfide in
fact, almost any combustible gas - - if
feasibility so indicates.
II BASIC COMBUSTION CONCEPTS AS
APPLIED TO FLARES:
A Gaseous fuels alone are flared because
they:
Burn rapidly with very low percentage
Consulting Engineer, Leonard C. Mandell Associates,
66 Pitman Street, Providence, Rhode Island.
PA. C. ce. 38. 1.67
of excess air resulting in high flame
temperatures.
Leave little or no ash residue.
Are adaptable to automatic control.
The natural tendency of most combustible
gases when flared is smoke:
An important parameter is the H/C ratio.
Experience has shown that with hydro-
carbon gases such as: Acetylene
with a H/C ratio = 0. 083, real black
soot will result from simple burning. .
Propane (C3H8) with a H/C ratio = 0. 22
creates black smoke.
Ethane (C?Hg) with a H/C = 0. 25 - a
bright yellow flame with light trailing
smoke will result. A H/C of 0. 28 gives
very little if any smoke, and methane
(CH4) with a H/C of 0. 33 gives a bright
yellow flame with no smoke.
If the H/C is less than 0. 28, then steam-
injection close to the point of ignition into
the flame makes the flare smokeless. It
should be noted that steam injection can be
applied to the point of clearing up the
smoke and reducing luminosity before
reaching the point of extinguishing the
flame. Hydrogen is the cleanest, most
rapid and highest-heat evolving fuel
component. It helps to: heat the carbon
and also provides for better carbon/oxygen
contact which results in cleaner burning;
also, the reaction of carbon monoxide to
carbon dioxide goes much easier in the
presence of water vapor.
In flare burning of sulfur-bearing com-
pounds: approximately 90% or more
appears as sulfur dioxide and 10-30% of
the (803) mutually appears as sulfur
trioxide. Blue grey smoke becomes
visible as the sulfur trioxide falls below
its dew point temperature.
B-71
-------
Flare Combustion
D In flare burning of chlorine-bearing
compounds, most will appear as hydrogen
chloride vapor. However, appreciable
quantities of chlorine will remain.
E A relation exists between the auto-ignition
temperature of the gas, its calorific
value and its ease of successful flare
burning.
At 800°F AIT: A minimum H. V. of
200 BTU/cu. ft. is required.
At 1150°F AIT: A minimum H. V. of
350 BTU/ cu. ft. is required.
At 1300°F AIT: A minimum H. V. of
500 BTU/cu. ft. is required.
F Since the heat content of many gases vary
much below 100 BTU/cu. ft. and since
complete burning is required regardless
of the weather; pilots are used to initiate
ignition of the flare gas mixtures, -- and
to help maintain flame temperatures to
attain rapid burning.
G Yellow-flame combustion results from
the cracking of the hydrocarbon gases that
evolve incandescent carbon due to inade-
quate mixing of fuel and air. - Some flames
can extend to several hundred feet in
length.
H Blue-flame combustion occurs when water
(steam) is injected properly to alter the
unburnt carbon.
I Flared gases must be kept at temperatures
equal to or greater than auto ignition
temperature until combustion is complete.
J Carbon monoxide burns rapidly with high
heat and flame temperature, whereas
carbon burns relatively slow.
K A smokeless flare results when an ade-
quate amount of air is mixed sufficiently
with fuel so that it burns completely be-
fore side reactions cause smoke.
What is Required? Premixing of air + fuel
Inspiration of excess air into the
combustion zone
Turbulence (mixing) and time
Introduction of steam: to react with
the fuel to form oxygenated compounds
that burn readily at relatively lower
temperatures; retards polymerization;
and inspirates excess-air into the
flare.
Note: 1) Steam also reduces the length of
an untreated or smokey flare by
approximately 1/3 of its length.
2) With just enough steam to eliminate
trailing smoke, the flame is usually
orange. More and more steam
eliminates the smoke and decreases
the luminosity of the flame to yellow
to nearly white. This flame appears
blue at night.
L The luminosity of a flare can be greatly
reduced by using say 150% of steam
required for smokeless operation. Since
a major portion of flame originates from
contained incandescent carbon.
M Water sprays, although effective in low-
profile, ground-flares, have not been
effective to date in elevated flares. The
water although finely atomized, passes out
and away from the flame without vaporiz-
ing or intimately mixing with burning
gases -- especially where any kind of wind
occurs. The plugging of spray nozzles
is also a problem - the "Rain" from
spray that may fall near base of stack
is very corrosive.
Ill TYPES OF FLARES:
Flares are arbitrarily classed by the elevation
at which the burning occurs; i. e. -- The
elevated-Hare, the ground-flare and the-Pit.
Each has its pros and cons. As should be
expected, the least expensive flare will
normally be used to do the required job-
compatible with the safety/welfare of the
Company and the Public.
B-72
-------
Flare Combustion
A Elevated Flares:
This type of flare provides the advantages
of desirable location in associated
equipment-areas with greater fire and
heat safety: also considerable diffusion/
dilution of stack concentrations occur
before the plume-gases reach ground
level.
Major disadvantages are:
1 Noise problems result if too much
steam is used
2 Air vibrations severe enough to rattle
windows 1/2 mile or more away.
There are 3 general types:
The non-smokeless flare which is
recommended for relatively clean,
open-air, burning gases such as hydro-
gen, hydrogen sulfide, carbon monoxide,
methane, and ammonia.
The smokeless flare which incorporates
steam injection to obtain clean burning
of low H/C ratio gases such as
acetylene, propylene, and butadiene.
The endothermic type which incorporates
auxiliary means of adding heat energy
to the vent gases of low heat contents
in the 50-100 BTU/cu. ft.). This Hare
may or may not operate smokelessly.
B Ground Flares: In general, ground flares
require approximately 2^ times as much
steam to be smokeless as elevated flares.
They also require much more ground
space. At least a 500 feet radius should
be allowed all around the flare. In addi-
tion to the burner and combustion
auxiliaries, ground flares also require a
ground-shield for draft control and at
times a radiant shield for heat and fire
protection. Hence, large open areas are
needed for fire-safety (plenty of real-
estate) and air pollution attenuation.
Ground flares do however offer the ad-
vantages of less public visibility and easier
burner maintenance. The cost of present-
day, ground flares as a rule are more
expensive than elevated flares. However,
they may also cost less depending upon
location requirements. Ground flares are
normally designed for relatively small
volumes, with a maximum smokeless
operation up to approximately 100, 000
standard cubic feet per hour of butane
or equivalent. There is heat sterilization
of areas out to a radius of approximately
100 ft. At least 3 types are known to the
author; the Esso multi-jet smokeless
and Non-Luminous Flare, the conventional
center nozzle with spray water for inspira-
tion of combustion-air; and the dry-type
for clean burning gases.
C The Pit: The venturi type is, as a rule,
the least expensive. It can handle large
quantities such as 14,000 cfm or
20,000, 000 cu. ft. /day. It consists of
one or more banks of burners set hori-
zontally in a concrete/refractory wall.
The other three-sides are earth-banks
approximately 4 ft. high. The typical
ground-area may be approximately
30 ft X 40 ft. The pit excavation may be
6 ft. deep, all burners discharge hori-
zontally. The burners may vary from the
simple orifice to the better venturi -
aspirating units with pressure-valve re-
gulation. Piping and appurtenances include
proper pitch, knock-out drums, liquid
seals, and constant-burning, stable pilots.
As a rule, burning pits are the least
satisfactory but also are least expensive.
However, if location and air pollution are
not significant, the pit method becomes
attractive.
B-73 and B-74
-------
CONTROL EQUIPMENT FOR INDUSTRIAL PARTICULATE EMISSIONS
T.L. Stumph
PART ONE
PRINCIPLES OF PARTICLE COLLECTION
I INTRODUCTION
Dust particles evolving from known sources and
confined to well-defined gas streams can be
removed from a carrier gas by various collect-
ion devices. Common reasons for particle
removal include:
A Recovering material for re-use in manu-
facturing processes or for sale as a
by-product.
B Desire to reduce quantity of particu-
lates discharged into the atmosphere.
II THE REMOVAL PROCESS
Particle removal can usually be broken down
into three distinct steps:
A Deposition of dust particles on a collect-'
ing surface by application of directional
forces other than that of the motion of
the gas stream.
B Retention of the particles on the collect-
ing surface without allowing them to be
re-entrained in the gas stream.
C Intentional removal of the particles from
the collecting surface by cleaning mecha-
nisms, either intermittent or continuous.
Ill COLLECTING MECHANISMS
By analyzing numerous collection devices, the
basic mechanisms for separating particles from
a gas stream can be reduced to the following:
A Gravity settling: The horizontal carrier gas
velocity is reduced sufficiently to allow the
particles to settle by force of gravity.
B Inertial forces: By suddenly changing the
direction of the gas flow, the greater momen-
tum of the particles causes them to depart
from the gas stream flow lines.
C Filtration: Dust-laden gas passes through a
porous medium upon which dust particles are
trapped, leaving a cleaner gae to be dis-
charged .
D Electrostatic attraction: Electrically
charged particles are attracted to objects
of an opposite charge.
E Particle conditioning: By causing intim-
ate contact of dust particles and water, a
heavier water-particle agglomerate is
formed. This can be more easily separated
from the gas stream by one of the other
collection mechanisms.
T.L. Stumph, at the time of writing,
was a Sanitary Engineer with Air Pollution
Training, Training Program, SEC
EAQM.VIII.8.66
B-75
-------
Control Equipment for Industrial Particulate Emissions
IV SELECTING A DUST COLLECTOR
The selection of a dust collector involves many
considerations.. Some are subject to scientific
rationale, and others are most often gained by
experience. Successful selection requires care-
ful balancing and evaluation of the following
factorsf
A Particle Characteristics
1. Size distribution
2. Shape
3. Density
A. Stickiness
5. Hygroscopicity
6. Electrical properties
B Carrier Gas Properties
1. Temperature
2. Moisture content
3. Corrosiveness
4. Flammability
C Process Factors
1. Gas flow rate
2. Particle concentration
3. Allowable pressure drop
4. Continuous or intermittent operation
5. Desired efficiency
6. Ultimate waste disposal
D Economic
1.. Installation cost
2. Operating cost
3. Maintenance cost
V COLLECTION EFFICIENCY
Any dust collector, operating under specific
flow conditions and with a given gas will
have a collection efficiency corresponding to
each particle size or particle size-distribu-
tion passing through the collector.. Thus,
there is a definite "particle size-collection
efficiency" relationship for every dust coll-
ector for given flow conditions.
The term "particle size" in this instance, re-
fers to an apparent size determined by measuring
the terminal settling velocity of a given par-
ticle in the carrier gas. Apparent size can be
calculated from Stokes Law, which expresses
terminal settling velocities for spherical par-
ticles under laminar flow conditions.. The
resulting "apparent size" would probably not be
identical to particle size determined by sieving
or microscopic methods because it includes the
effect of particle shape and density in addition
to size.
Particle diameter determined in this manner is
the equivalent spherical diameter the particle
would possess if its density is equal to the
average density of the aggregate dust being
analyzed. Thus, the resulting particle diame-
ter is directly related to the particle's
terminal settling velocity which in turn ex-
presses the behavioral characteristics of the
particle in a fluid.
When referring to over-all collection efficien-
cy, particle size-distribution is the most
important and often the least considered para--
meter. A typical size-distribution curve for
dusts found in air pollution sources is shown
in Figure 1.
5 >«! u
O) C J_
&-- 10
Figure 1.
Particle size (y)
(logarithmic scale)
TYPICAL SIZE-DISTRIBUTION CURVE
FOR AN INDUSTRIAL DUST
If the curve is normal (symmetrical about a
vertical axis) when plotted on semi-logarith-
mic paper, the curve is said to be "log-normal".
This situation occurs frequently for industrial
dusts normally encountered in waste gas streams.
Each dust has some type of size-distribution
curve, plotted on suitable coordinates, that
adequately describes its size characteristics.
B-76
-------
Control Equipment for Industrial Particulate Emissions
01
D-
0)
r-
O
§
U
01
s
Particle size (p)
Figure 2. TYPICAL SIZE-EFFICIENCY CURVES
The effect of particle size on efficiency of
a collector can be demonstrated by collecting
dust samples on the inlet and outlet of the
operating collector.. Knowing the inlet and
outlet dust concentration, and the inlet and
outlet size distributions, collection effici-
ency can be plotted as a function of particle
size on arithmetic coordinates. The resulting
plot, known as a "size-efficiency" curve, des-
cribes the performance capabilities of the
collector in question when operating at stated
gas flow conditions (velocity, viscosity, etc.).
The collector would have a different "size-
efficiency" curve for each new gas flow condi-
tion, but the curve would remain unchanged for
different dust concentrations and different
size distributions. Thus, for any particle
size passing through a given collector, a def-
inite and predictable collection efficiency
will be observed, flow conditions remaining
constant. "Size-efficiency" curves are espec-
ially useful in predicting over-all collection
efficiency for a specific dust having known
size-distribution characteristics- Some typi-
cal " size-efficiency" curves are shown in
Figure 2. Steeper curves indicate "more effi-
cient" collectors or those having greater
collection efficiency for small particles.
REFERENCES
1 Silver-man, Leslie. Modern Methods for the
Control of Air Pollution, presented at
a meeting of the Sanitary Section, Boston
Society of Civil Engineers, March 3, 1954.
2 Stephan, David G. Dust Collector Review,
Transactions American Foundrymen's
Society, 1960.
3 Foley, R.B. Terminal Velocity as the
Measure of Dust-Particle Characteristics,
Transactions A.S.M.E., February, 1947.
Lunde, K.E., and Lapple, C..E» Dust and
Mist Collection - A Critique on the
State of the Art, Journal Air Pollution
Control Association. February, 1958.
Drinker, P., and Hatch, T. Industrial
Dust, McGraw-Hill Book Co., Inc.,
New York, 1954.
B-77 and B-78
-------
INDUSTRIAL PROCESSES WHICH DISCHARGE PARTICULATE EMISSIONS*
1 Introduction
Approximately 6 million tons of dust, fume,
and mist, were discharged from industrial pro-
cesses and industrial fuels fired in 1966- This
quantity would be considerably greater if high-
efficiency collectors were not used by many in-
dustries. However, the total would be drastic-
ally lower if existing control technology were
employed to the fullest.
Some industries inherently create more
particulate air pollution than others, and for
such industries one or two specific operations
dominate the emission picture. In a given in-
dustry, particulate releases to the atmosphere
are generally proportional to production rates.
Often these discharges can be reduced dramati-
cally through process changes or by the use of
collection devices.
Table 1 lists many of the industries that re-
lease large quantities of particulate matter. As
discharged, these particles include dry dusts,
combustible oil and tar mists, inorganic acid
mists, and combinations of these and other
pollutants. The same processes frequently re-
lease gaseous pollutants, some of which may be
more objectionable than the particulate matter.
Although this discussion is limited to particulate
matter, some remedial measures also affect
sulfur oxides, odors, or other gaseous
contaminants.
The industries which are cited in the follow-
ing pages commonly use several types of fired
heaters and boilers. Particulate emissions as-
sociated with this equipment, for the most part,
are functions of the fuel burned. Combustion
principles developed generally apply, but the
combustion processes are not cited unless spe-
cific problems are associated with them.
2 Iron and Steel Mills
The major sources of particulate matter in
iron and steel mills are blast furnaces, steel-
making furnaces, and sintering plants. Coke
ovens, which are operated as adjuncts to steel
mills, are discussed in Section . 9-
2. 1 Sintering Plants - Major sources of
dust in sintering plants are the combustion gases
drawn through the bed and the exhaust gases
from sinter grinding, screening, and cooling
operations. Exhaust temperatures of the com-
bustion gases range from 160° to 390° F. One
6000-ton-per-day plant operates at 350° F.
About 50 percent by weight of the particles
* Taken from Control Techniques for Particu-
late Air Pollutants, National Air Pollution
Control Administration Publication No. AP-51
discharged from a sintering machine are larger
than 100 microns. Because dust generated in
the sintering operation can be returned to the
process, most plants are equipped with cyclones,
which, because of the large particle size, usu-
ally operate at over 90 percent efficiency by
weight. However, cyclone exit loadings range
from 0. 2 to 0. 6 grains per cubic foot. High-
efficiency baghouses and electrostatic precipita-
tors, therefore, offer promise of much better
collection. However, few have been applied to
sintering machines.
2. 2 Blast Furnaces - Iron ore, coke, and
limestone are charged into a blast furnace to
make iron. Under normal conditions the una-
bated gases from a blast furnace contain from 7
to 30 grains of dust per standard cubic foot (scf)
of gas. Most of the particles are larger than
50 microns in diameter. The dust contains about
30 percent iron, 15 percent carbon, 10 percent
silicon dioxide, and small amounts of aluminum
oxide, manganese oxide, calcium oxide, and
other materials. Blast furnace gas cleaning
systems normally reduce particulate loading to
less than 0. 01 grain per standard cubic feet to
prevent fouling of the stoves where the gas is
burned. These systems are composed of settling
chambers, low efficiency wet scrubbers, and
high efficiency wet scrubbers or electrostatic
precipitators connected in series.
2. 3 Steel Furnaces - The three most im-
portant types of steel-making furnaces are open
hearth furnaces, basic oxygen furnaces, and
electric furnaces. Relative usage as a percent
of total production of each of these furnaces in
1958, 1966, and 1967 is shown in Table 2.
Average emission rate from a hot-metal
open-hearth furnace is about 0. 4 grain per scf
for a conventional furnace and 1. 0 for an oxygen-
lanced furnace, 'i ° Up to 90 percent of the par-
ticles are iron oxide, predominantly FE2O3- A
composite of particles collected throughout a
heat show that about 50 percent were less than
5 microns in size. Control of iron oxide requires
high-efficiency collection equipment such as
venturi scrubbers and electrostatic precipitators.
Because of the cost involved and the growing
obsolescence of open hearth furnaces, industry
has been reluctant to invest money in the re-
quired control equipment. Often these furnaces
have been replaced by controlled basic oxygen
furnaces and electric furnaces.
More emissions are created by the basic
oxygen furnace than by the open-hearth furnace.
B-79
-------
Table 1 - INDUSTRIAL PROCESS SUMMARY
oo
o
Industry or process
Iron and steel mills
Gray iron foundries
Annual capacity,
1000 tons
(except as noted)
149, 000
17,350
Number
of
plants
184
1,400
Nature
Iron oxide dust.
Iron oxide dust,
Paniculate emissions
Principal sources
smoke Blast furnaces, steel making
furnaces, sintering machines.
smoke, Cupolas, shakeout systems, core
Other emissions
CO, combustion products
Odors, combustion products,
Non-ferrous smelters
Petroleum refineries and
asphalt blowing.
Portland cement
Kraft pulp mills
Asphalt batch plants
Acid manufacture:
Phosphoric
Sulfuric
Coke manufacturing
Glass furnaces and glass
' fiber manufacture.
Coffee processing
Cotton ginning
Carbon black
Soap and detergent
manufacturing.
Gypsum processing
Coal cleaning
2,721
3 ,-650 x 106 bbls. a
500 x 106 bbls. b
30,000
2,300
20,513
54,278
1,496
oil and grease, metal
fumes.
2, 500 Smoke, metal fumes, oil
and grease.
318 Catalyst dust, ash, sul-
furic acid mist, liquid
aerosols.
180 Alkali and product dusts
88 Chemical dusts, mists
Aggregate dusts
66 Acid mist, dust
223 Acid mist
60 Coal and coke dusts,
coal tars.
Sulfuric acid mist, raw
material dusts, alkaline
oxides, resin aerosols.
Chaff, oil aerosols, ash
dehydrated coffee
dusts.
Cotton fiber, dust and
smoke.
37 Carbon black
Detergent dusts
Product dusts
Coal dusts
making.
Smelting and melting furnaces
Catalyst regenerator, sludge
incineration, air blowing of
asphalt.
Kilns, coolers, dryers, material
handling systems.
Chemical reclaiming furnaces,
smelt tanks lime kilns.
Dryers, material handling systems.
Thermal processes - phosphate
rock acidulating, grinding and
handling system.
Charging and discharging oven
cells, quenching, material
handling.
Raw material handling, glass
furnaces, glass fiber forming
and curing.
Roasters, spray dryers, waste
heat boilers, coolers, stoners,
conveying equipment, chaff
burning.
Gins, trash incineration
Carbon black generators
Spray dryers, product and raw
material handling systems.
Calciners, dryers, grinding and
material handling systems.
Washed coal dryers
hydrocarbons from contam-
inated scrap.
SOX combustion products
Hydrocarbons, SOX, H%S, odors
Combustion products
Odors, SOX
Odors, combustion products
HF, SOx, odors
Phenols, H2S
Combustion products
Defoliants and insecticides
Combustion products, odors
Combustion products
Combustion products
a Barrel - 42 gallons.
b Barrel - 376 pounds.
-------
Process Emissions of Particulates
Table 2. STEEL PRODUCTION, PERCENTAGE
BY PROCESS4
Percent of total
Furnace type
1958
1966
1967
Open hearth
Basic oxygen
Electric
90. 7
1. 5
7. 8
72. 1
17.4
10. 5
55.6
32.6
11. 8
The principal portion of the increase in emis-
sions is caused from furnace oxygen blowing.
Emissions of about 5 grains per scf are reported
as typical. ^ Particle size is small; 85 percent
are smaller than one micron in diameter. ^ All
basic oxygen furnaces in the United States are
equipped with high-efficiency electrostatic pre-
cipitators or venturi scrubbers.
Electric furnaces are usually used for alloy
production, and because of their flexibility, are
becoming popular for most metal melting opera-
tions. Emissions from electric furnaces often
reach particulate matter concentrations of 3
grains per scf. Only 40 to 50 percent of the dust
is iron oxide, an amount considerably smaller
than that emitted by other furnaces. The parti-
cles are difficult to collect because of a strong
tendency to adhere to fabric surfaces, a high
angle of repose, and a high electrical resistivity,
and because they are difficult to wet. Approxi-
mately 70 percent by weight of the particles are
smaller than five microns and 95 percent by
number are smaller than 0. 5 micron in diameter.
Nevertheless, except for difficulties inherent in
the charging operation, over 95 percent effective
collection can be achieved with appropriate hood-
ing and high-efficiency collection equipment.
Baghouses are especially suited for such
collection.
3 Gray Iron Foundries
Melting cupolas are the principle sources of
particulate matter at iron foundries. Casting
shake-out systems, sand handling systems,
grinding and deburring operations, and coke-
baking ovens are other sources.
Cupola exhaust gases are hot and volumi-
nous, and contain significant portions of com-
bustible matter and inorganic ash. The most
effective control system incorporates an after-
burner to eliminate combustibles and a fabric
filter to collect the inorganic dust and fume.
Coolers must be used ahead of the baghouse to
protect fabric filters from the heat of the ex-
haust gas. Most such systems use glass fabrics,
but some synthetic cloths have been found to be
satisfactory. Even though baghouse control sys-
tems provide excellent particle collection, they
have not met with wide acceptance, principally
because of cost. 10 Dry centrifugal collectors
and scrubbers with various efficiencies are used
in many instances. High-efficiency scrubbers
are reported to provide about the same perfor-
mance as fabric filters, but visible emissions
are more pronounced.
Casting shake-out and sand cleaning are
dusty operations that are normally well control-
led. For these operations baghouses are com-
monly used; medium-efficiency scrubbers and
dry centrifugal collectors are also used.
Core ovens create relatively smaller quan-
tities of particulate matter, much of which is in
the form of finely divided liquid aerosols. Emis-
sions from core ovens are similar to those dis-
charged from paint baking and resin curing op-
erations with odors being more objectionable
than the particulates. A properly designed after-
burner will criminate most of the particulates
and malodors.
4 Petroleum Refineries
Major sources of particulate matter at re-
fineries are catalyst regenerators, airblown as-
phalt stills, and sludge burners. Lesser sources
include fired heaters, boilers, and emergency
flares.
In modern fluidized catalytic crackers, fine
catalysts are circulated through the reactor and
regenerator vessels. From 100,000 to 150,000
cfm of hot, dusty gases are vented from a large
regenerator. Dust collectors as well as carbon
monoxide waste heat boilers are often used to
control air pollution. It is common practice to
install a carbon monoxide boiler to use the fuel
value of the clean gas stream exiting from the
particulate collector.
In typical installations 2-stage or 3-stage
cyclones are located in the regenerator vessels
of FCC units for catalyst recovery and reutiliza-
tion. In some cases external cyclones are in-
stalled to reduce the particulate content of the
flue gases leaving the regenerators of these units.
Catalyst dust losses from the regenerator equip-
ped with internal cyclones and in some cases
supplemented by external cyclone equipment can
range in the order of 100 to 350 pounds per hour
depending on the size, age, and basis of design
of the unit.
Electrostatic precipitators may also be used
to collect the fine particles from the regenerator
exit gases and some refiners have reported cata-
lyst dust losses as low as 40-60 pounds per hour
although typical current installations have higher
emission rates. The percent efficiency of the
precipitators is a function of the inlet dust load-
ing from the regenerator and the desired emis-
sion rate to the atmosphere.
Airblowing of asphalts generates oil and tar
mists and malodorous gaseous pollutants. It is
common practice to scrub the oils and tars from
the hot (300 to 400°F) gas stream. Seawater is
sometimes used for this purpose. In any case,
separators are necessary to reclaim the oil and
prevent contamination of effluent water. After-
burners are used to incinerate the uncondensed
B-81
-------
Process Emission of Particulates
gases and vapors, which can constitute an odor
nuisance.
At petroleum refineries, the open burning or
incineration of sludges can be a major source of
particulate matter and sulfur dioxide emissions.
These sludges are a mixture of heavy petroleum
residues and such inorganic materials as clay,
sand, and acids. Because the materials cannot
be separated readily, sludge is usually atomized
in much the same way as heavy fuel oil. The or-
ganic fraction can be burned effectively in such
an incinerator, but any inorganic matter is en-
trained in exhaust gases. High-efficiency pre-
cipitators, baghouses, and high-energy scrub-
bers are among the stack cleaning devices that
are available to collect the fine dusts; the final
choice of control unit would be based upon the
nature of the sludge. Sulfur dioxide collection
would not be affected. However, if there is an
accessible sulfuric acid plant, sludge may be
conditioned and used as part of the acid plant's
feed material. Very low grade sludges may be
dumped at sea. It must be emphasized that in-
cineration alone is not the solution for the dis-
posal of all forms of refinery waste sludges.
Solvent extraction is another method for recover-
ing the organic fraction and the separated "clean"
solids are acceptable to normal landfill sites.
5 Portland Cement
Both mining of raw materials and manufac-
ture of cement create dust. Dust is generated
at the blasthole drilling operation at the quarry,
during blasting at the rock face, and during
loading of trucks. At the primary and secondary
crushing plants, in the grinding mills, at blend-
ing and transfer points, and in the final bagfilling
and bulk truck or railroad car loading operations,
where the particulate-laden air is at ambient
temperatures, bag filters are usually the best
means of control. * '
Rotary dryers used in dry process cement
plants may be a major source of dust generation
and require collecting systems designed for
higher temperatures. Dust concentrations of
5 to 10 grains per scf entering the collector are
normal. Baghouses or combinations of multiple
cyclones and baghouses are frequently used.
Newer dry process cement plants incorporate
the drying operation into the raw grinding cir-
cuit. In such a "dry-in-the-mill" combination
drying and grinding circuit dusts are normally
vented to a baghouse.
The largest sources of emissions at cement
plants are direct-fired kilns for burning Portland
cement clinker. Exit gas particulate loadings
are usually 5 to 10 grains per scf for wet kilns
and 10 to 20 grains per scf for dry-process kilns.
Exhaust gases from wet-process kilns contain
considerably more moisture than gases from dry
process kilns. The volume of the hot (500° to
600°F) kiln gases may exceed 250,000 cubic feet
per minute. Over 85 percent by weight of gas-
borne particles are smaller than 20 microns in
diameter. The most prevalent chemical con-
stituents are calcium oxide (CaO), about 41 per-
cent; silicon dioxide (SiC^), 19 percent; and alu-
minum and iron oxides (Al2O^ + Fe2(~>i), 9 percent.
The balance would be predominately CC^- ^
Electrostatic precipitators are widely used
to control particulate emissions from kilns.
Fabric filters of siliconized glass bags have been
installed on both wet and dry process kilns.
Each control device has been successful when
adequately designed and properly maintained.
6 Kraft Pulp Mills
The major source of particulate emissions
in kraft pulping is the recovery furnace in which
spent cooking liquors are burned to remove the
organic materials dissolved from the wood to
recover the inorganic cooking chemicals. Sodium
sulfate is the major chemical released as particu-
late matter. Small amounts of sodium carbonate,
salt, and silica, and traces of lime, iron oxide,
alumina, and potash also are emitted. Because
95 to 98 percent of the total alkali charged to the
digester finds its way to the spent liquor, it is
economically imperative that it be recovered.
Electrostatic precipitators of about 90 per-
cent efficiency are used to recover particles
emitted from recovery furnaces. New installa-
tions call for design efficiencies of about 97. 5
percent, and at least one such unit has a design
efficiency of over 99. 9 percent.
Other sources of particulate matter are
smelt tanks and lime kilns. Stack dust from
lime kilns can be collected in 85 to 90 percent
efficient venturi scrubbers. Water sprays of 20
to 30 percent efficiency and mesh demisters of
80 to 90 percent efficiency are usually used on
smelt tanks.
7 Asphalt Batching Plants
Hot asphalt batching plants are potential
sources of heavy dust emissions.
Asphalt batching involves the mixing of hot,
dry sand, aggregate, and mineral dust with hot
asphalt. Although conveyors and elevators gen-
erate some dust, the major source is the direct-
fired dryer used to dry and heat aggregates. Exit
gases range from 250° to 350° at volume rates of
15,000 to 60,000 standard cubic feet per minute
(scfm). Most dryers employ simple cyclone sep-
arators which collect 70 to 90 percent of the dust
entrained in the exit gases. Nevertheless, the
remaining dust in the gas stream usually totals
more than JOOO pounds per hour and further dust
controls are needed in most areas.
Centrifugal and baffled scrubbers have been
used with success in many areas to control the
fine dust which escapes the primary cyclone.
High efficiencies are reported - some exceed
99. 0 percent - with losses from most tested
plants ranging from 20 to 40 pounds per hour. It
is common to vent elevators and major conveyor
transfer points to the scrubber. 13
B-82
-------
Process Emissions of Participates
As high temperature fabrics were developed.
fabric filters found greater acceptance at asphalt
batch plants. Such filters have been used suc-
cessfully at asphalt batch plants since 1950. Re-
cently, several were installed in Chicago,
Illinois, in an effort to obtain better dust control
than had been afforded with scrubbers. They are
reported to provide excellent collection of fine
particles with little or no visible emissions from
the baghouse. Although fabric filters frequently
are more expensive than scrubbers, they collect
dry "fines" which may be useable in high-grade
asphaltic concrete mixes. In addition they ob-
viate the need for holding ponds and preclude
water problems.
8 Acid Manufacture
Most of the particulate matter attributed to
acid manufacture is created in the production of
sulfuric and phosphoric acids. Manufacture of
the other two major industrial acids - nitric and
hydrochloric does not generate large amounts
of acid mist.
8. 1 Sulfuric Acid - Over 90 percent of the
sulfuric acid in the United States is manufactured
by the contact process. In the process sulfur
or other sulfur bearing materials are burned to
sulfur dioxide (SC^) and catalytically converted
to sulfur trioxide (SO^). Uncontrolled emissions
range from 0. 05 to 0. 23 grain per scf of exit
gas. Concentrations depend to a large degree on
plant design and proper operation of the acid ab-
sorber. Most modern plants are equipped with
high-efficiency electrostatic precipitators or
mesh eliminators in which 99 percent of the acid
mist is recovered. Acid mists are usually con-
trolled to a far greater extent than gaseous SC>2
releases.
The primary source of emissions in the
chamber process is the final Gay Lussac tower.
Combined sulfuric acid mist and spray in the
exit gas ranges from 0. 08 to 0. 46 grain per scf.
8. 2 Phosphoric Acid Two processes are
used to manufacture phosphoric acid. High-
purity acid for the food and detergent industries
is produced by burning elemental phosphorous.
The process is similar to the contact sulfuric
acid process. The oxidation product, phosphor-
ous pentoxide (P2O^), is hydrated and absorbed
in phosphoric acid. Mist is collected from ex-
haust gases with electrostatic precipitators or
high pressure drop mesh entrainment separators.
Acid mists escaping collection are extremely hy-
groscopic so that visible emissions are pro-
nounced unless high collection efficiencies are
achieved. High-purity phosphorous for this pro-
cess is manufactured in electric furnaces, which
create gaseous fluorine compounds and solid
particulates.
The wet process is used to produce less
pure phosphoric acid for the fertilizer industry.
During the manufacturing process, sulfuric acid
is reacted with phosphate rock. Except for ma-
terial handling and grinding operations few par-
ticulates are generated. However, the acidula-
tion reaction liberates large quantities of gaseous
silicon tetrafluoride (SiF^), and scrubbers are
required.
9 Coke Manufacture
Metallurgical coke is the solid material re-
maining after distillation of certain coals. About
90 percent of the United States coke output is
used for production of blast furnace iron.
Conventional coking is done in long rows of
slot-type coke ovens into which coal is charged
through holes in the top of the ovens. Coke oven
gas or other suitable fuel is burned in the flues
surrounding the ovens, to furnish heat for coking.
Flue temperature is about 2600° F and the coking
period averages 17 to 18 hours. At the end of the
coking period, incandescent coke is pushed out of
the furnace into quenching cars and carried to a
quenching station, where it is cooled with water
sprays.
The beehive oven is a simpler type of coking
oven. Distillation products from this oven are
not recovered. Its use has diminished with the
development of the byproduct oven. The process
persists because of an economic advantage during
peak production periods. Capital investment is
lower and inoperative periods can be tolerated.
About 1. 5 percent of the total coal coked in 1967
was produced in these ovens. A very large part,
i.e., 25 to 30 percent of the coal charged to these
ovens is emitted to the atmosphere as gases and
particulate matter. Ducting these emissions to
an afterburner appears to be a feasible method
of control.
Coal and coke dust emissions result from
coal car unloading, coal storage, crushing and
screening, the coking process (where the largest
releases of particulate dust occur during larry
car coal charging of the byproduct oven and push-
ing of the product coke to quench cars), quench-
ing, and final dumping from the quench car.
Slot type coke ovens currently being designed
include the following features that speed opera-
tions and minimize leaks:
1. Better designed and thinner-walled heat-
ing flues to improve heat transfer and
minimize cool spots and undercoking.
This results in a cleaner pushing opera-
tion.
Z. Improved refractories, with less spal-
ling and cracking. These refractory de-
fects cause warping of metal furnace
parts, gas leaks into flue systems and
chimneys, and voids which fill with
undercoked coal and cause smoke during
pushing.
3. Gas-tight, self-sealing oven doors, that
minimize manual sealing with clay.
B-83
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Process Emissions of Particulates
4. Mechanical cleaners or self-sealers for
doors and for top-charging hole covers.
A few grains of sand on a metal seat can
cause appreciable leakage of hot gases.
5. Sealing sleeves for leveling bars.
Leveling bars are used to even out the
oven charge to allow free passage of
gas over the charge into the gas collec-
tor main.
6. Mechanical removal of top coal-
charging lids and means to charge all
three holes of an individual oven rapidly
and simultaneously, with gas recovery
mains in operation.
7. Steam jet aspirators in byproduct header
ducts.
8. Anintercell header to normalize the cell
pressure throughout the battery.
9. Charging car volumetric sleeves and
dust entrainment chutes.
10. Wooden baffling to separate particulate
matter from quench tower effluent
gases.
A breakthrough in coke manufacturing tech-
nology is needed to improve operations. ^ Im-
provements have been slow. Installations
exist that have employed supposedly superior
charging and discharging equipment, but satis-
factory operations have not been achieved. A
joint research effort by several steel companies
has been under way for 5 years to develop new
coke manufacturing technology, but potential
commercial applications appear to be five years
away
16
Another form of coke, used in blast furnace
refractories and in the manufacturing of elec-
trodes for large steel and aluminum reduction
furnaces, is calcined petroleum coke. Petro-
leum coke is a refinery product, but is seldom
calcined by the refinery. Calcining occurs in a
rotary kiln at 1700° F removing absorbed water
and heavy oil and forming a marble-size product.
Volatilized hydrocarbons are usually passed to a
2200° F combustion chamber before being re-
leased to the atmosphere. Subsequent convey-
ance of the dusty product to the storage requires
hooding and enclosed ducting. The dust is abra-
sive and causes heavy wear on bucket elevators
and other transfer equipment. Control of par-
ticulate matter can be accomplished during load-
ing of the coke. One system uses concentric
tubing; the inner filling tube carries the coke
and the outer tube exhausts entrained dust from
the enclosed railroad car, truck or ship hold.
Baghouses are used to capture dust from loading
as well as dust generated at other handling and
transfer points.
10. Primary and Secondary Recovery of
Copper, Lead, Zinc, and
Aluminum
Primary smelting of lead and zinc involves
converting the sulfide of the ore to an oxide
through roasting, and subsequent reduction of the
metal oxide to its metallic state in a separate
vessel. Copper, however, requires a prelimin-
ary smelting step, during which the naturally
occurring complex sulfide is reduced to the
cuprous sulfide, CuSg, by mixing the charge with
limestone. The cuprous sulfide is then converted
to blister copper in a converter where the sulfur
is removed by oxidation. Sulfur dioxide gas is
released from these operations, along with par-
ticulate matter which is largely sublimed oxides,
dust, and acid mists. When sulfur dioxide emis-
sions exceed 3 percent of these furnace exhaust
volumes, a sulfuric acid manufacturing plant is
feasible. Pretreatment of the smelter gases
going to the acid is required to remove particu-
late matter. If sulfur dioxide recovery is not
practiced, fiberglass demisters or precipitators
are usually used to remove particulate material
from smelter exhaust gases.
Most materials fed to secondary recovery
furnaces are alloys of copper, zinc, tin, or lead
in the form of solid scrap and drosses. Gases
from the furnaces may contain as fumes oxides
of the low boiling metals. Particularly bother-
some are submicron lead and zinc fume. Zinc
oxide fume particle size ranges from a high of
0. 5 micron to a low of 0. 03 micron. Baghouses
are usually used to control these oxide fumes;
where the fumes are corrosive, electrostatic
precipitators are used. Soiled scrap metal
melting may evolve grease or oil fumes as smoke
during the heatup phase. Incineration of the
smoke with a control afterburner is necessary
if the metal cannot be cleaned before melting.
Metallic aluminum is produced by the elec-
trolytic reduction of alumina (A^O-j) in a bath of
fused cryolite by the Hall-Heroult process. Cell
operating temperatures range from 1700° to
1800° F. The gases generated in the cells are
corrosive and toxic, and consist of hydrogen
fluoride and volatilized fluorides. Some fine
particulate matter is entrained in the exit gases.
Water scrubbers have long been used for collec-
tion of both the particulate and corrosive gases.
Some installations have used baghouses with
alumina coated cloth filter bags. '
Secondary aluminum recovery operations
produce particulate matter from the fluxes used,
from impurities in the scrap, and from chlor-
ination of the molten aluminum. Oily or greasy
scrap gives off smoke. When chlorine gas is
used to degas the melt or remove magnesium,
hydrogen chloride gas and aluminum chloride
fume are evolved. The fume is difficult to col-
lect because of its small particle size and hygro-
scopic nature. Water scrubbers are used to
collect the gaseous contaminants.
11 Soap and Synthetic Detergent
Manufacture
Principal sources of particulate matter in
the making of soap and synthetic detergents are
the spray drying of products and the handling of
dry raw materials. The wet chemical processes
B-84
-------
Process Emissions of Participates
used to make soaps and detergents are relatively
innocuous from the particulate standpoint, al-
though malodorous gases and vapors are gener-
ated in some instances.
Gases from the spray dryers, discharged at
approximately 200° F, contain large amounts of
moisture. In addition, the product is sticky at
these temperatures so that dry collection in
fabric filters or electrostatic precipitators is
difficult. Multiple cyclones may be employed as
precleaners, but scrubbers are used almost
exclusively to collect fine dust. Moderate pres-
sure venturi units or baffled scrubbers provide
adequate control in many instances. These
scrubbers usually use slurries rather than mere-
water and product is recovered from the slur-
ries. Residual fine particles, together with high
moisture levels, frequently impart marked
opaqueness to the stack gases. It is sometimes
possible to avoid this problem by adding some of
the less stable ingredients to the product after
the spray drying operation.
Fabric filters are widely used in soap
detergent plants to control dusts generated from
the handling of products and raw materials and
from packaging operations.
12 Glass Furnaces and Glass Fiber
Manufacture
Reverberatory furnaces are used to produce
nearly all glass products. The furnaces and raw
materials generate significant quantities of
particulate matter.
Glass furnaces are usually heated with oil or
natural gas, which is fired directly over the melt.
Heat is reclaimed in checkerwork regenerators
used to preheat combustion air. Raw materials
are charged at one end of the furnace and molted
glass is pulled from the other end. Gullet (scrap
glass), limestone, soda ash, and sand are the
main ingredients fed to the furnace melter sec-
tion. Glass temperatures are as high as 2700° F
in the furnace, but are usually near 2200° F at
the point of discharge. Particulate matter in
exhaust gases is traceable to two principal
sources: (1) Fine raw materials that are entrain-
ed in combustion gases before they are melted;
and (2) Materials from the melt, such as sulfur
trioxide created by sulfate decomposition and
other solids picked up by escaping carbon dioxide
gases. Sulfur trioxide and the oxides of potas-
sium, sodium, and calcium are the main con-
stituents of particulate emissions. Losses from
large furnaces range from less than 10 pounds
per hour to as high as 100 pounds per hour. Most
units release less than 40 pounds per hour.
Particulate releases tend to be affected by feeder
designs and the makeup of raw materials.
Operators control emissions through furnace
design, electric heating, and raw material con-
trol rather than with stack cleaning devices.
Control of emissions with fiberglass filters is
feasible, but the particulate matter is extremely
difficult to handle.
In the manufacture of glass fiber, the emis-
sions from the forming processes are considered
unacceptable both from the standpoint of odor and
visible particles. Although suitable control
methods are not at hand, it appears that a com-
bination of process changes and stack controls
will be required to render exit gases acceptable
in many communities. These methods are being
developed and prospects are good that satisfac-
tory techniques will be found. Afterburners have
been employed with success at curing ovens
where volumes are low in comparison to forming
lines.
13 Carbon Black
Because of the extremely fine size (0. 01 to
0.4 micron) and fluffy nature of carbon black
particles, they are readily emitted from improp-
er handling and transferring operations and dur-
ing separation of them from the process gases.
Emissions have been particularly heavy from
channel black process plants. The furnace black
process (oil and gas) accounts for 94 percent of
the total production and technology is available
to control emissions from these plants.
Furnace temperature is kept at about 2500°F
and the black-laden gases are cooled to 450°
and 550° F before entering the dust collecting
equipment. The preferred system consists of
an agglomerator followed by a baghouse. Coated
fiberglass bags last about 12 months. The overall
particulate collection efficiency of such a system
is about 99 percent. The combination of cyclone
and electrostatic precipitator is no longer satis-
factory because it collects only about 60 percent
of the particulate matter.
14 Gypsum Processing
Gypsum, the basic ingredient of plaster and
wallboard, is manufactured by grinding, drying,
and calcining gypsum rock. At most plants much
of the gypsum is processed into wallboard in
highly mechanized systems. Grinding, drying,
and calcining processes are principal sources of
dust. Handling, packaging, and wallboard man-
ufacture are of secondary potential.
Most grinding operations are controlled with
fabric filters. Fine grinders often are equipped
with built-in pneumatic conveyors that allow the
product to be collected in the filter.
Gypsum is dried in direct-fired dryers to
remove free moisture before calcining. Exit
gases of about 220° F contain a large amount of
fine dust.. Electrostatic precipitators, bag-
houses, or scrubbers are almost always used to
remove this dust from exit gases.
The calcining operation is conducted at
400° to 450° F in externally heated kettles or
conveyors. In general, exit gases from the
calcining operation are less voluminous than
those from dryers. Historically, electrostatic
precipitators have been used to control cal-
ciners. Dust collection has not always been
B-85
-------
Process Emissions of Particulates
adequate, and baghouses now find better accep-
tance. Most new gypsum plants have been equip-
ped with fabric filters. High-temperature fabrics
are required and heaters have to be installed to'
prevent moisture from condensing in duct work.
Baghouses are used extensively in modern
gypsum plants to collect dust from various con-
veying and processing points. In most instances
a salable product is reclaimed.
15 Coffee Processing
The processing of green coffee beans and the
production of dehydrated instant coffee generate
dust and liquid aerosols as well as odorous gases.
The most prominent sources are roasters, spray
dryers, waste heat boilers, and green coffee
cleaners.
Roasters are the predominant sources of oil
aerosols and odors but also create significant
amounts of solid particulate matter. Chaff, a
flaky membrane from the bean, and other solids
are collected in simple cyclones at temperatures
of 400° to 500° F. Remaining aerosols and
odorous gases may be incinerated in afterburners
at temperatures ranging from 1200° to 1400° F.
Coolers and stoners create additional solid
particulate matter, but few aerosols or malodors.
Cyclones normally provide adequate dust control .
With some continuous systems, the exit of roaster
gases through close coupled coolers requires the
use of afterburners on the cooler exhaust stream.
Spray dryers not unlike those used in other
industries are used to produce instant coffee. If
the dryer is operated properly, very little fine
particulate matter is generated and satisfactory
dust control can be achieved with dry multiple-
cyclone collectors. Periodic excursions can be
expected with resultant discharges of fine dust.
Many plants operate scrubbers or baghouses
downstream of mechanical collectors. Collected
fines are blended with the main product stream.
Dust recovered in dry collectors is of sufficient
value to make it attractive to maintain collector
efficiencies.
At instant coffee plants, large quantitites
of leached coffee grounds are produced. Many
operators burn the spent grounds in waste heat
boilers similar to coal-fired boilers. Particulate
emissions are dependent on the type of firing and
the ash content (usually about 4 percent by weight
of dry grounds). A common design incorporates
an underfeed stoker and auxiliary gas burners.
Green coffee cleaning and handling creates
dust and chaff which normally can be handled well
in simple cyclones.
16 Cotton Ginning
The major source of particulate matter in
cotton ginning are the gin itself and the subse-
quent incineration of the trash. Relatively
coarse materials are emitted from the ginning
operation and relatively fine materials escape
the associated lint cleaner. High-efficiency
B-86
multiple-cyclones successfully collect the coarse
particles, and the recently developed stainless
steel in-line filter is effective on the fine
particles.
Disposal of the cotton trash by composting,
rather than incineration, is being practiced in
some parts of the country. Incineration of trash
generates a large portion of the particulate
matter released from uncontrolled ginning plants.
-------
Process Emissions of Particulates
REFERENCES
1. Brandt, A. D. "Current Status and Future 11.
Prospects - Steel Industry Air Pollution
Control. " In: Proceedings of the 3rd
National Conference on Air Pollution,
Washington, D. C. , 1966, pp. 236-241.
2. Schueneman, J. J. , High, M. D. , and 12.
Bye, W. E. "Air Pollution Aspects of the
Iron and Steel Industry. " U. S. Dept. of
Health, Education, and Welfare, Div. of
Air Pollution, Cincinnati, Ohio, PHS-
Pub-999-AP-l, 1963, 129 pp.
13.
3. McGannon, Harold E. "The Making,
Shaping, and Treating of Steel. " U. S.
Steel Corporation, 8th edition, 1964,
p. 404.
4. "Annual Statistical Report. " American 14.
Iron and Steel Institute, 1967 edition,
pp. 66, 68.
5. Schueneman, J. J. , High, M. D. , and
Bye, W. E. "Air Pollution Aspects of
the Iron and Steel Industry. " U. S. Dept. 15.
of Health, Education, and Welfare, Div.
of Air Pollution, Cincinnati, Ohio,
PHS-Pub-999-AP-l, 1963, p. 45.
6. Brandt, A D. "Current Status and
Future Prospects Steel Industry Air 16.
Pollution Control. " In: Proceedings of
the 3rd National Conference on Air Pol-
lution, Washington, D. C. , 1966, pp. 236- 17.
241.
7. Schueneman, J. J. , High, M. D. , and Bye,
W. E. "Air Pollution Aspects of the Iron
and Steel Industry. " U. S. Dept. of
Health, Education, and Welfare, Div. of
Air Pollution, Cincinnati, Ohio, PHS-Pub-
999-AP-l, 1963, p. 67.
8. Schueneman, J. J. , High, M. D. , and
Bye, W. E. "Air Pollution Aspects of
the Iron and Steel Industry. " U. S. Dept.
of Health, Education, and Welfare, Div.
of Air Pollution, Cincinnati, Ohio, PHS-
Pub-999-AP-l, 1963, p. 68.
9. Schueneman, J. J. , High, M. D. , and
Bye, W. E. " Air Pollution Aspects of
the Iron and Steel Industry. " U. S. Dept.
of Health, Education, and Welfare, Div.
of Air Pollution, Cincinnati, Ohio, PHS-
Pub-999-AP-l, 1963, p. 61.
10. Sterling, M. "Current Status and Future
Prospects Foundry Air Pollution Con-
trol. " In: Proceedings of the 3rd National
Conference on Air Pollution, Washington,
D. C., Dec. 1966, pp. 254-259.
Doherty, R. E. "Current Status and Future
Prospects Cement Mill Air Pollution
Control. " In: Proceedings of the 3rd Na-
tional Conference on Air Pollution,
Washington, D. C. , 1966, pp. 242-249.
Doherty, R. E. "Current Status and Future
Prospects - Cement Mill Air Pollution
Control. " In: Proceedings of the 3rd Na-
tional Conference on Air Pollution,
Washington, D. C. , 1966, pp. 242-249.
Ingels, R. M. , Shaffer, N. R. , and
Danielson, J. A. "Control of Asphaltic
Concrete Plants in Los Angeles County. "
J. Air Pollution Control Assoc. , 10(1):
29-33, Feb. I960.
"Atmospheric Emissions from Sulfuric
Acid Manufacturing Processes. " U. S.
Dept. of Health, Education, and Welfare,
Div. of Air Pollution, Cincinnati, Ohio,
PHS-Pub-999-AP-13, 1965, 127 pp.
Brandt, A. D. "Current Status and Future
Prospects - Steel Industry Air Pollution
Control. " In: Proceedings of the 3rd Na-
tional Conference on Air Pollution,
Washington, D. C. , 1966, pp. 236-241.
Brandt, A. D.
June 11, 1968.
Private communication,
"Impregnated Fabrics Collect Fluoride
Fumes. " Engineering and Mining, J. ,
Vol. 160, No. 5, May 1959.
B-87 and B-88
-------
OPACITY PROBLEMS CAUSED BY WATER VAPOR
Frank L. Cross, Jr., P.E.
Dr. Philip R. Sticksel**
I. Introduction
The ease of monitoring a control area by
visual observation has led to the enact-
ment of regulations prohibiting plumes
which obscure more than a certain per-
centage (frequently 40 percent) of an
observer's view when he looks through the
plume. One of the problems confronting
control officials using regulations
which depend upon the visual determination
of equivalent opacity is that of
evaluating plumes containing large
quantities of water vapor. This water
vapor, when it condenses and becomes
visible, may make the plume 100 percent
opaque even though the quantity of other
particulate material is small enough so
that the plume, if dry, would not be in
violation of the opacity standard.
II. Is Water Vapor a Pollutant?
The question arises as to whether equivalent
opacity regulations should distinguish be-
tween those plumes that contain water vapor
and those that do not. Water alone is not
injurious to health, and is normally present
in any atmosphere, either in the invisible
vapor state or in a visible liquid state in
the form of fog or clouds. Arguments can
be advanced for the beneficial effects of
increasing the relative humidity of the
atmosphere by the discharge of water vapor
from industrial processes.
There are also objections to water vapor
emissions. Under certain topographical
and meteorological conditions, the arti-
ficially created water vapor is a con-
tributing factor to a higher frequency
of ground fogs. These can be dangerous
if they form in the vicinity of a high-
way or air field, because they decrease
the visibility. Industrial accidents,
also resulting from the decreased visi-
bility, may occur within the area of
the emitting factory. In freezing
weather, there is a possibility of in-
creased ice formation because of the
presence of higher atmospheric relative
humidity. Even though the emission may
be a pure water vapor, there is the
possibility that a combination of the
vapor and other substances in the air
will create a harmful pollutant. -This
may occur in the vicinity of large
power plants; when water vapor emitted
from cooling towers in large quantities
and sulfur oxides emitted from coal
burning equipment combine in the air
to form sulfuric acid mist, the damage
to vegetation and materials may be far
greater than would be expected if there
was no water vapor emission.
Finally, there may be an objection based
on aesthetic grounds, to dense plumes re-
gardless of their composition. The aver-
age citizen cannot distinguish between a
white plume, which is primarily water va-
por, and one of the same color which
contains only a small percentage of water.
III. Regulations Governing Wet Plumes
While ordinances in some air pollution codes
make no distinction between the visible
evaluation of water vapor and non-water
plumes, other air pollution regulations do
make provisions allowing for the emission of
"uncombined water." Questions can arise
about the interpretation of this term as
to whether it means "chemically" uncombined.
Even though the intent of the regulation
may be to allow for only pure steam plumes,
one may argue .that no water vapor, either
naturally or artificially produced, can
condense unless it contains some particle
as a nucleus for the water drop.
Deputy Chief (Acting) Institute for Air
Pollution Training, Office of Manpower
Development, NAPCA
**Meteorologist, Field Studies and Enforcement
Section, Institute for Air Pollution Training
Office of Manpower Development, NAPCA
PA. LA. 48.-9.69
B-89
-------
Opacity Problems Caused by Water Vapor
One method of "reading" wet plumes is to
instruct the plume inspector to observe
these plumes at the point where the water
vapor has evaporated. This prevents the
citation of a plume containing a dry opacity
below the legal limit, but which because of
the accompanying water, exceeds the opacity
limit. This method, however, may protect
a polluter because the dry opacity of his
plume may exceed the legal limit near the
stack. But at the point where the water
evaporates, the plume has dispersed enough
so that its opacity becomes legally
acceptable.
IV. Visible Identification of Water Vapor Plumes
A. Atmospheric Effects on Water Vapor
Water in the gaseous state (as water
vapor) is invisible and is always
present in the atmosphere. One of the
measures of the volume of water vapor
contained in the atmosphere is relative
humidity; the more water vapor con-
tained in a given amount of air,
the higher the relative humidity
content. When the air is "saturated"
with water vapor, the relative humidity
present is 100 percent. Any additional
water vapor must condense out into the
liquid state and will become visible in
the plume.
The amount of the water vapor held in
the air varies with the temperature
of the air. Warm air can hold more
water vapor than cold air. Con-
sequently, air that is not saturated
with water vapor may be cooled until
it becomes saturated and the relative
humidity then reaches 100 percent.
If this cooling is done at constant
pressure, the temperature at which
saturation occurs is called the dew
point. If the air is cooled below its
dew point, it will be supersaturated
and the excess water vapor condenses
out into the liquid form of a cloud.
When wet plumes are initially created
in a process, the gas temperature may
be hot enough so that the water is
invisible and is in the vapor form.
If the plume is cooled sufficiently,
either in the stack or in the atmos-
phere, then the plume becomes saturated
with water vapor and condensation takes
place. As the plume is mixed with the
surrounding air, some of the moisture
in the plume is transferred to the
ambient air. This Increases the re-
lative humidity of the ambient air and
decreases the relative humidity of the
plume. When the relative humidity of
the plume reaches 100 percent; the
visible water begins to change by
evaporation to an invisible vapor.
In time the water plume completely
disappears.
Under varying atmospheric temperatures
or humidity conditions, two plumes that
are emitted from a given process under
identical conditions may form and then
dissipate at different distances from
the stack. In cold weather a plume may
condense, and become visible, as soon
as it leaves the stack. In hot weather
not as much atmospheric cooling occurs
and condensation may not take place
until the effluent has moved some dis-
tance from the stack. This latter
condition results in a detached plume.
Once formed, the plume disappears more
quickly into the warmer air which can
hold additional water vapor without
becoming saturated. For example, on
two days with identical temperatures:
the plume will persist for a longer
distance on the day with a higher re-
lative humidity, because the ambient
air can hold less water vapor and
cannot absorb additional moisture
from the plume. Some materials,
such as sulfur trioxide (SO^) are
hygroscopic, and tend to attract the
water vapor in the air. These plumes
can remain visible to the observer
for longer distances.
B. Identifying Visible Plumes
A pure water vapor plume disappears
without a trace of dust. It evaporates
quickly, mixes in all directions, and
is characterized by its "wispiness."
When plumes are observed under varying
atmospheric conditions, those contain^
ing large amounts of water vapor may be
distinguished by their reactions. The
wet plume may be detached from the stack
in warmer weather and it will persist
for longer distances during periods of
high relative humidity.
Plumes containing large amounts of
sulfur trioxide will become visible
as detached plumes, when the rela-
B-90
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Opacity Problems Caused by Water Vapor
tive humidity of the ambient air is
high because the 803 is hygroscopic.
For the same reason, they will also
persist for longer distances than
the pure water vapor plumes.
V. Typical Operations which Discharge
Water Vapor
A. Drying Operations
1) Type of Equipment
a. Rotary dryers
b. Spray dryers
c. Drum dryers
d. Tray and tunnel dryers
2) Type of Industry
a. Powdered milk
b. Chemicals
c. Pharmaceuticals
d. Instant coffee
e. Detergents
f. Ores
g. Paper
B. Combustion Operations in which Fuels
Containing Hydrogen and Hydrocarbons
Are Used
C. Air Pollution Control Operations which
Use Water Scrubbing to Remove Solids
or Pollutant Gases
1) Typical Equipment
a. Venturi scrubbers
b. Packed towers
c. Spray towers
D. Cooling Operations in Which the Heat
is Removed by Water Evaporation
VI. Methods of Eliminating Visible Wet Plumes
A. Several methods are available to
eliminate condensation of the steam
plume from a stack:
1> Dilution of the Plume with Heated
Air
Hot air can be mixed with the
moist effluent to reduce the dew
point and thus prevent the effluent
from becoming super-saturated as
it enters into the colder air.
(An example of this method will be
given later).
2) Superheating the Plume
The plume is heated (before
emission) to a temperature which
is high enough to disperse the
effluent in the atmosphere, before
it has cooled to the dew point.
3) Direct-Contact Condensation with
Water
The effluent can be cooled to its
dew.point by bringing the plume
into direct contact with cold wa-
ter. There are several ways to
accomplish this direct-contact
cooling:
a. Surface water
b. Cooling tower
c. Air-fin cooler
A) Indirect-Contact Condensation with
a Surface Condenser
If contamination of the cooling
water with the effluent is a
problem, then the plume can be
cooled by passing it through a
tubular surface condenser which
contains circulating water. The
three methods listed in VI-A-3
can also be applied to indirect
cooling.
5) Combination Processes
When the outdoor temperature is
low, the problem of preventing
condensation of the plume becomes
more difficult because the air
contains less water vapor before
it becomes saturated. Under these
conditions a combination of methods
must be used e.g. removing some
of the moisture by condensation
and then reheating the plume
before discharging it.
B. Problems
1) When the plume is superheated or
diluted with heated air, these
gases and heat are added to the
atmosphere:
a. Carbon dioxide from the com-
bustion process which supplies
the heat.
b. Thermal pollution from the
heat itself.
B-91
-------
Opacity Problems Caused by Water Vapor
Atmosphere
STACK
142,000 Ib./hr. Feed material = 25,000 Ib./hr.
31,800 cfm. Feed water = 12,000 Ib./hr.
20 C. Flow rate = 48 gpm.
Temp. = 88 C.
Y
ATDurATro , ^ ^PftAY HP
143,042 Ib./hr.
69,200 cfm.
1,032 Ib./hr. 300 C.
340 cfm. H,0 = 3.52 by vol.
J80
Produc
23,430 Ib.
Noncondensables = 140,272 Ib./hr.
Water = 15,740 Ib./hr
Dust = 6 Ib./hr.
Dewpoint = 75 C. (134.5 F.)
Temp. = 90 C. (194 F.)
RECYCLE CYCLONIC
SCRUBBER
Noncondensables = 140,272 Ib./hr.
Water = 14,760 Ib/hr.
C. Dust = 1,570 Ib./hr.
t Volume = 52,850 cfm.
ih Temp. = 107 C.
Dewpoint = 56 C.
Natural gas
Figure 1. Flow chart
2) When the water vapor in the plume
is prevented from condensing in
the atmosphere (by use of the
direct-contact condenser cooling
method) certain requirements must
be considered:
a. A large quantity of cooling
water must be available.
b. The cooling water will pick
up and convert some of the
air contaminants into water
pollutants.
c. The cooling water will absorb
some of the heat from the
plume. If the volume of heat
is large enough, thermal pol-
lution may become a problem.
3) When the water vapor contained in
a plume is condensed by direct or
indirect contact condensation with
water vapor, there will still be a
discharge of water vapor into the
atmosphere. This discharge will
be transferred from the stack, to
a cooling tower or the surface of
a river or lake, where it may be-
come considered to be less object-
ionable to the community.
VII. Costs of Removing Wet Plumes
Figure 1 illustrates the process flow dia-
gram for a twenty (20) feet diameter
multiple purpose spray dryer. The estimated
costs (as of 1968) of the various methods
for eliminating the condensed water plume
from this dryer are given in Tables I and
II. These costs were developed for
atmospheric temperatures which are just
above the freezing point.
The most economical method, on an annual
operating cost basis, is direct condensa-
tion with natural surface water; however,
natural water is not always available.
The only method that minimizes air, water
and thermal pollution (condensation with a
surface condenser using an air-fin cooler)
is the second most expensive one.
B-92
-------
Opacity Problems Caused by Water Vapor
REFERENCES
1. Ringelmann, M., "Methods d'Estimation
des Fumes Produites par les Foyers
Industrials," La Revue Technique, 268
(June 1898).
2. Marks, L. S., "Inadequacy of the Ringel-
mann Chart," Mech. Eng., 681 (Sept.,
1937).
3. Health and Safety Code, State of
California, Chap". 2, Sec. 24242 (1947).
4. Yocom, J. E., "Problems in Judging Plume
Opacity," J. Air Poll. Control Assn.,
13, 36-39 (Jan., 1963).
5. Connor, W. D., Hodkinson, J. R., "Optical
Properties and Visual Effects of Smoke-
stack Plumes," U.S. Dept of HEW, Public
Health Service, Publication 999-AP-30,
Cincinnati, 1967, pp. 23-28, 58-59.
6. Tukey, J. W., et al., "Restoring the
Quality of Our Environmental Pollution
Panel of the President's Science
Advisory Committee, the White House,
(Nov., 1967), pp. 71-72.
7. Crocker, B. B., "Water Vapor in Effluent
Gases: What to Do About Opacity
Problems" Chemical Engineering (July
15, 1968)
8. Sheehy, J. P., Achinger, W. C., Simon,
R. A., "Psychrometric Chart" Handbook
of Air Pollution U. S. Dept. of HEW,
Public Health Service, pages 11-9
11-14.
B-93 and B-94
-------
STANDARDS FOR PARTICULATE EMISSIONS
C. A. Lindstrom
I FORMS OF EMISSION STANDARDS
Air pollution control agencies usually divide
emissions to the atmosphere into three
broad categories: (1) visible, (2) particulate,
and (3) gaseous. Hence, forms of emission
standards are commonly based on: (1) opacity,
(2) solid pollutant content, (3) gaseous pol-
lutant content, and (4) odor content of the
effluent emitted to the atmosphere.
When emission standards overlap, all perti-
nent regulations apply. For example,
compliance with a rule concerning the particu-
late pollutant content of an effluent does not
free one from the need to simultaneously
comply with a rule which regulates the
opacity of the plume if both rules are
specified.
E EMISSION OPACITY STANDARDS
A Applicability
Opacity standards are applicable only
when a gaseous effluent contains sufficient
quantity of particulate matter, or colored
gas, to make the plume visible to the naked
eye as some degree of color. Visible
plumes are those which consist of any one
or combination, of the following pollutants.' '
1 A sufficient concentration of a colored
gaseous pollutant, such as, nitrogen
dioxide (brown to yellow), bromine
(reddish-brown), iodine (purplish), and
chlorine (greenish-yellow). With the
exception of these gases, however,
virtually all gaseous pollutants important
in air pollution are colorless.
2 Suspended particulates of such charac-
ter and concentration that their presence
is evident to the sight.
B The Ringelmann Chart
1 Application
The Ringelmann Chart is a method of
judging the shade of grey of a particu-
late laden plume emitted from a source
of combustion. It is assumed that the
darker the shade of grey, the greater
the concentration of black-colored
particulate matter in the plume. The
particulate matter imparting the black-
ness consists mostly of soot, flyash,
and other solid and liquid particulates
less than 1-micron in diameter.
It must be cautioned that application of
the Ringelmann Chart, alone, for the
determination of the shade of grey of
any plume, provides no specific
measurement of the concentration of
pollutant in the effluent.
2 Description
The Ringelmann Chart consists of four
5 3/4" X 8 1/2" charts, each with a
rectangular grill of black lines on a
white background. I The width and
spacing of the black lines are designed
so that each chart presents a certain
percentage of black. Thus Ringelmann
No. 1 is equivalent to 20% black;
Ringelmann No. 2, 40% black;
Ringelmann No. 3, 60%; Ringelmann
No. 4, 80%; and Ringelmann No. 5,
100%.
3 Use of the chart
a Use as an actual reference for the
observer.
One use of the chart is as an actual
reference for the observer while he
Carl A. Lindstrom is
Chief, Field Studies Section
State of Arizona
PA.A.le.30a.9.69
B-95
-------
Standards for Participate Emissions
is judging the shade of grey of a
plume. The chart is supported at
eye-level at an observation point
that is between 100-feet and 1/4-mile
from the stack, and which provides
an obstructed view of the plume.
The plume should be at right angles
to the direction of observation, and,
have as a background, only the
diffused light of the sky during the
day. The observer takes a position
at a distance from the chart (usually
about 50-feet). where the black and
white areas appear to merge into
varying shades of grey. The shade
of the plume is then visually compared
with the shades of grey indicated by
the chart; and Ringelmann number
identified according to the Ringelmann
shade the plume mostly resembles.
Variables which affect the reading
and must be taken into consideration
include the thickness of the plume,
cloud and wind conditions, position
of the sun relative to the observer,
the human element in judging shade,
the need to re-focus the eyes from
the plume to the chart, and the effect
of transmitted light from the plume
and reflected light from the chart.
b Use for certification of observers.
An observer may be trained to
judge the Ringelmann shade pre-
sented by a plume without having
the chart before him as an actual
reference. To accomplish this,
the observer is trained with smoke-
generating equipment that produces
a plume of any desired Ringelmann
shade. By repeated reference to the
chart during the training period, the
shades of the Ringelmann scale
become fixed in the observer's
memory. Those that pass the train-
ing course are certified as observers,
and, their observations are accepted
as evidence in courts of law.
c Use as a reference for special
field measuring devices
In its official form as a sheet of
printed paper, the Ringelmann
Chart is not conveniently adaptable
to routine field use. To overcome
this objection, a number of special
measuring devices, all based on the
Ringelmann scale of shades of grey,
have been devised. Among these
are the Smoke Tintometer, the
Umbrascope, the Smokescope, the
Smoke Guide, and the Powers Micro-
Ringelmann Chart. ^« 3)
4 Ringelmann Shade Ordinance Provisions
a Limiting shades
Taking into consideration the un-
economical expenditure to remove
particulate pollutants from an ef-
fluent so that an invisible plume
will result, regulations usually
allow the emission of a light haze.
Most American air pollution control
legislations permit Ringelmann No. 1
at all times. A lesser number allow
Ringelmann No. 2 or No. 3 at all
times (Table 1). (as of 1969)
b Private homes
Early regulatory applications of the
Ringelmann scale exclude private
homes. However, present tendency
is to apply opacity criteria to all
visible emissions regardless of
source. The most recent approach
is to apply the most stringent opacity
standards in residential areas where
air must be the cleanest. '^'
c Other than private homes
For other than private homes, regula-
tory statements commonly express
not only a limiting Ringelmann shade,
but also an exception to the limit.
In general, the exception to the limit
B-96
-------
Standards for Participate Emissions
prohibits "a Ringelmann shade
darker than A for more than B
minutes in any period of C minutes. "
(Table 2)
The concept of a time B within
time-period C is historical, and
has as its basis, time allowances
for smoke released when starting
coal-fired boilers, the necessity
for blowing flues, and the inherent
operating peculiarities of steam
locomotives. Although equipment
modernization may erase the need
for a concept so based, once the
concept is embedded in legislation
it is difficult to revise.. For present-
day legislation, time B for con-
tinuously fed fuel-burning equipment
is merely an allowance for operating
emergencies (e. g., E of Table 2).
The short time-period C in regula-
tory statements concerning a mobile
source permits evaluation of the
plume shade before the source passes
out of the observer's view. For
modern stationary continuously fed
fuel-burning sources, a long time-
period C is used and strict regula-
tion placed over period B.
Advantages of Ringelmann Shade
Ordinances
a Ease of enforcement
Since the Ringelmann opacity stand-
ards are specific with reference to
allowable shades of the plume and
time-period for their existence,
they are simply and directly
enforced.
b Ease of inspection
An inspector needs only to observe
a plume darker than that permitted
for a specific interval of time in
order to cite a violator.
c Reduction of particulate pollutant
concentration in effluents
As the concentration of particulate
pollutant in the plume increases,
the transmission of light through
the plume decreases exponentially.
Hence, in order to have the plume
appear a lighter grey, one attack
would be to decrease the concentra-
tion of particulate pollutant in the
effluent. Enforcement of the
Ringelmann standard, therefore,
may aid considerably in accomplish-
ing gross reduction of atmospheric
pollutants in a community by forcing
the application of adequate control
methods to sources of emission.
C The Equivalent Ringelmann Opacity Concept
No chart or guide is presently available
for measuring opacity of plumes other than
grey. However, California courts of law
have ruled that an observer certified to
mentally distinguish gradations of grey
can mentally translate an equivalent scale
of gradations of colors other than grey.' '
Hence, the "equivalent opacity" concept
has been used by the Los Angeles County
Air Pollution Control District, California
and the Bay Area Air Pollution Control
District, California with legal success.
(4)
D Judging Wet or Detached Plumes
The observer is unable to determine the
opacity of "wet" or "steam" plumes, and
of detached plumes, due to particulate
pollutant. The following examples show
the need for further research in these
areas.
If a wet collector is to control the concen-
tration of particulate matter in an effluent,
the plume is likely to be highly opaque;
most of the opacity being caused by water
droplets which are not considered atmos-
pheric pollutants. Hence, if a "wet";
plume is judged strictly upon its equivalent
Ringelmann opacity, it may violate the
opacity limitation, particularly when the
weather is cold and humid. Mere applica-
tion of equivalent Ringelmann opacity to
B-97
-------
Standards for Particulate Emissions
the "wet" plume provides no adequate
proof that the presence of water droplets
is, op is not, the only reason the observed
opacity exists.
A somewhat similar situation may exist for
the effluent from a phosphoric acid plant.
The opacity of the plume depends upon
the size of droplets suspended therein,
and the size of the droplets is dependent
upon ambient humidity. Here, too, mere
application of the equivalent Ringelmann
concept does not identify the opacity due
to P2Oej alone.
A plume with high SO^ or 303 resulting
from the combustion of fuel with high
sulfur content may have a transparent
portion immediately above the stack for a
short distance downwind, and then an
opaque stream from thereon (detached
plume). Thus, argument concerning
violation of an opacity-based rule may
arise here, also.
Relative Cost of Compliance to Opacity
Regulations
Fine particulates between 0. 1 to 1-micron
scatter more light per unit mass than
these larger or smaller. '*' Therefore,
if compliance to opacity regulations re-
quire efficient removalof particulates in
this size range, more expensive collectors
are usually demanded than those necessary
to comply with concentration-based rules.
Ill GRAVIMETRIC EMISSION STANDARDS
A Forms of Gravimetric Emission Standards
Gravimetric emission standards may be«
based on (1) the weight concentration of
particulate matter in the effluent (weight of
pollutant per unit volume or unit weight of
effluent), or (2) the weight rate of emission
of particulate matter to the atmosphere.
B Concentration-Based Regulations
1 Application
a Combustion sources
Concentration-based regulations
apply to sources of combustion
where it is possible to correct the
concentration to some standard
condition such as a certain percent
excess air, CO2» or 03, in the
effluent, so as to account for deliber-
ate dilution with air.
b Non-combustion sources
Concentration-based regulations are
also applied to effluents other than
those originating from combustion
sources. These limits may, or may
not, be integrated with process
weight-based regulations depending
upon the probability of deliberate
dilution of the effluent with air to
reduce concentration. (Tables 3
and 4).
Examples of concentration-based
emission regulations
a Coal-fired steam power plant
emissions
1) Traditional regulations
The following regulation had its
beginning in the "Model Smoke
Ordinances" of the American
Society of Mechanical Engi-
neers and was a compromise
representing what could be
achieved using economical
dust collectors on small plants
built between 1900 and about
1940.
The limiting concentration rec-
commended in this publication
is 0. 85 pounds of particulate
matter per 1000 pounds of flue
gas adjusted to 50% excess air,
or to 12% CO2. (Fifty percent
excess air is nearly equivalent
to 12% CO2 for bituminous coal.)
Translated into other units,
this concentration is equivalent
B-98
-------
Standard for Particulate Emissions
to 0. 25 grains of particulate
matter per cubic foot of flue
gas referred to 30 in. Hg. and
500°F. or to 0. 45 grains of
particulate matter per cubic
foot referred to 30 in. Hg. and
60°F. A further restriction is
sometimes imposed, for ex-
ample, the specification that
not more than 0. 21 grains per
cubic foot (30 in. Hg. 60°F)
shall be larger than 44-microns
or that 0. 2 pounds per 1000
pounds of flue gas be not larger
than 325 mesh United States
standard sieve.
2) Modern regulations
Even when the standard of 0. 85
pounds of flyash per 1000
pounds of flue gas was being
developed, it did not repre-
sent the best practice in new
plants then being constructed.
Flyash regulations adopted
during the past fifteen years
require lower emission rates.
An example of present regula-
tions converted to a BTU
basis is shown in Figure 1.
b Oil-fired steam power plant
emissions
Los Angeles County Air Pollution
Control District limits particulates
in emissions from oil-fired
steam power plants to 0. 30 grain
per cubic foot (30 in. Hg. 60°F)
reduced to 12% CO2-
C Rate of Emission Regulations
1 Current concepts
There are three current concepts under-
lying the regulation of rate of emission
of pollutants to the atmosphere. One
concept relates allowable rate of pol-
lutant emission to process weight rate;
another relates allowable rate of pol-
lutant emission to potential rate of
pollutant emission; and the third relates
allowable rate of emission to subsequent
ground-level concentrations at distances
downwind.
2 Application
In theory, for non-combustion sources,
it would be possible to easily by-pass'
regulations by merely diluting the
effluent with air, thereby lowering the
concentration. (Increased air handling
cost, however, may make such a
practice uneconomical). Therefore,
corrections to standard conditions
(e. g., % excess air, CO2. or 0% in the
effluent) are impractical for such
sources, making weight concentration
of particulate matter in the effluent a
poor measure of particulate pollutant
emission. Thus, concentration-based
regulations are supplemented by rate of
pollutant emission regulations to control
non-combustion sources of such nature.
3 Examples of the process weight rate
concept
Figure 2 shows the relationships
between permissible emission rate of
particulate pollutant and weight rate
of materials processed for various
air pollution control organizations.
(The process weight is the total weight
of all materials used in the process
excluding air, gas, and oil, but in-
cluding solid fuels.) Additional pro-
visions may be made. For example.
Bay Area Air Pollution Control District
provides that compliance with the
process weight regulation need not
require the effluent to be cleaner than
set forth in Table 3; Los Angeles County
Air Pollution Control District limits
emission concentrations to 0. 4 grains
per cubic foot at 30 in. Hg. , 60°F.
Such regulations are tailored to the
peculiarities of the manufacturing
operations in the area to which they
are to apply, and are designed to
permit maximum collection of particu-
late pollutant with control equipment
that is available and within economic
reach.
B-99
-------
Standard for Particulate Emissions
REFERENCES
1 Air Pollution Control Field Operations
Manual. Los Angeles County Air
Pollution Control District. Public
Health Service. Publication No. 937.
1962.
2 Ringelmann Smoke Chart. U. S. Bureau
of Mines Information Circular 7718.
1955.
3 Stern. A.C. Air Pollution. Vol. H.
Academic Press. New York. 1962.
4 Yocom, J. E. Air Pollution Regulations -
Their Growing Impact on Engineering
Decisions. Chemical Engineering.
July 23, 1962.
5 Current Guides for Prevention of New Air
Pollution. New York State Air Pollution
Control Board. Albany, New York.
1962.
6 Atmospheric Contamination and Purifica-
tion. Reprinted from Ind. and Eng.
Chem. November, 1949.
B-100
-------
Standards for Particulate Emissions
Table 1. ' U.S. CITIES ALLOWING RINGELMANN NO. 2 and NO. 3
Ringelmann Number Allowed
No. 2 for short periods
only
No. 2 at all times
No. 3 at all times
Scale varies with installa-
tion
No. scale
Number of Cities
63
30
1
5
3
102
Percent
62
29
1
5
3
100
Table
SMOKE ORDINANCE PROVISIONS (Poughkeepsie, N.Y.)
Type of Installation
Limiting Density, Shade of Smoke
Domestic installations, primarily for
heating and hot water, in one and two
family dwellings.
Installations, primarily for heating
and hot water in apartment houses,
office buildings, schools, hotels,
loft buildings, hospitals and other
installations of similar character.
All other stationary installations
except those included in Paragraph E.
D Railroad locomotives
E*For installations using a fuel in-
put in excess of 25,000,000 BTU/hr.,
the primary purposes of which are
to provide standby and emergency
facilities for maintaining essential
public utility services.
Not darker than Shade
Not darker than Shade Itl except
that smoke not darker than Shade 03
is permitted for not more than a
total of 4-minutes in any period of
30-minutes.
Not darker than Shade //2 except that
smoke not darker than Shade #3 is per-
mitted for not more than a total of
4-minutes in any period of 3-minutes.
Not darker than Shade #2 except that
smoke not darker than Shade #3 is
permitted for not more than 1/2-minute
in any period of 3-minutes.
Not darker than Shade #2 except that
smoke not darker than Shade #3 is
permitted for not more than a total
of 10-minutes in any period of 30-
minutes .
*This is a special purpose provision
to meet a situation unique to this
community. Special purpose provisions
of this type are not uncommon.
B-101
-------
Standards for Particulate Emissions
I
o
u
u>
3
T3
O
a
1
o
2.0
10 100 1000 10,000
Input - Million BTU/HR
*Based on 13,000 BTU, 10% ash Coal and 85% of ash fired entering collector.
Figure l.(3)
10 20 30 40 50 60 70 80 90
PROCESS WEIGHT, TONS/HR.
1. Los Angeles County, Calif.
2. Orange County, Calif.
3. Riverside, Calif.
4. Sarasota County, Fla.
5. Riverside County, Calif.
Figure 2.
(4)
6. Bay Area, Calif.
7. Vancouver, B.C.
8. Seattle, Wash.
9. San Bernardino, Calif.
B-102
-------
METEOROLOGIC FUNDAMENTALS
D. B. Turner*
RADIATION
The energy expended in the atmospheric
processes originally was derived from the
sun. This transfer of energy from the sun
to the earth and its atmosphere is by radi-
ation of heat by electromagnetic waves.
The'radiation from the sun has its peak of
energy transmission in the visible range
(0. 4 to 0. 7 microns) of the electromagnetic
spectrum but releases considerable energy
in the ultraviolet and infrared regions as
well. The greatest part of the sun's energy
is emitted at wave lengths between 0. 1
and 30 microns. Some of this radiation is
reflected from the tops of clouds and from
the land and water surfaces of the earth.
The general reflectivity is the albedo and
for the earth and atmosphere as a whole is
36 per cent, for mean conditions of cloud-
iness over the earth. This reflectivity is
greatest in the visible range of wavelengths.
When light (or radiation) passes through a
volume containing particles whose diameter
is smaller than the wavelength of the light,
scattering of a portion of this light takes
place. Shorter wavelengths scatter most
easily which is the reason the scattered MO
light from the sky appears blue. Sunlight,
near sunrise and sunset, when passing
through a greater path-length of the atmos- "°
phere appears more red due to the in-
creased scattering of shorter wave lengths. m
Absorption of solar radiation by some of
the gases in the atmosphere (notably water
vapor) also takes place. Water vapor, al- KAOIATON 300
though comprising only 3 per cent of the /LANGUYS \
atmosphere, on the average absorbs about °AY
six times as much solar radiation as all 20°
other gases combined. The amount of
radiation received at the earth's surface is m
considerably less than that received outside
the atmosphere.
The earth reradiates energy in proportion
to its temperature according to Planck's
law. Because of the earth's temperature,
the maximum emission is about 10 microns,
which is in the infrared region of the spectrum.
The gases of the atmosphere absorb some
wave length regions of this radiation. Water
* Meteorologist, Air Resources Cincinnati
Laboratory ESSA, NAPCA, Cincinnati,
Ohio.
PA. ME. el. 5a. 12. 62
vapor absorbs strongly between 5. 5 and 7
microns and at greater than 27 microns but
is essentially transparent from 8 to 13
microns. Carbon dioxide absorbs strongly
between 13 and 17.5 microns. Because of
the absorption of much more of the terres-
trial radiation by the atmosphere than of
the solar radiation, some of the heat energy
of the earth is conserved. This is the
"greenhouse" effect.
Figure 1 shows as a function of latitude the
amount of solar radiation absorbed by the
earth and atmosphere compared to the long
wave radiation leaving the atmosphere. The
sine of the latitude is used as abscissa to
represent area. It can be seen that if there
were no transfer of heat poleward, the
equitorial regions would continue to heat
up and the polar regions continue to cool.
Since the temperatures remain nearly the
same for various areas of the earth, such
a transfer does take place. The required
transfer of heat across various latitudes is
given in Table 1.
20 » 40 » M 70
SINE Of LATITUDE
* SOLA! RADIATION AtSOIIED >Y CAITH AND ATMOSPHERE
I LONG WAVE RADIATION LEAVING THE ATMOSPHERE
FIGURE 1
B-103
-------
ftfeteorologic Fundamentals
Table 1. Required Flux of Heat
Toward the Poles Across Latitudes
(1019 calories per day)
From Houghton
Latitude
0
10
20
30
40
50
60
70
80
90
Flux
0
4.05
7.68
10.46
11.12
9.61
6.68
3.41
0.94
0
(along meridions i. e. between poles and
equator) circulation is broken into three
cells shown in Figure 2 according to
Palmen's model. nf considerable impor-
tance is the fact that the jet stream does
not remain long in one position but meanders
and is constantly changing position. This
causes changes in the location of the polar
front and perturbations along the front. The
migrating cyclones and anticyclones re-
sulting, play an important part in the heat
exchange, transferring heat northward both
as a sensible heat and also latent heat. Also
a small amount of heat is transferred pole-
ward by the ocean currents.
THE GENERAL CIRCULATION
The previous section has indicated the
necessity of transfer of heat from the
warm equatorial regions to the cold polar
regions in order to maintain the heat
balance of the atmosphere. This thermal
driving force is the main cause of atmos-
pheric motion on the earth. The rotation
of the earth modifies this motion but does
not cause it since the atmosphere essen-
tially rotates with the earth. The portion
of the earth near the equator acts as a
heat source and the polar regions as a
heat sink. The atmosphere functions as
a heat engine transforming the potential
energy of heat difference between tropics
and poles to kinetic energy of motion which
transports heat poleward from source to
sink.
If the earth did not rotate, rising air above
the equator would move poleward aloft
where in giving up some of its heat would
sink and return toward the equator as a
surface current. Since the earth does
rotate, the Coriolis force (to be discussed
in the section on wind) deflects winds in
the northern hemisphere to the right.
Therefore flow from the tropics toward
the poles become more westerly and flow
from the poles toward the equator tends to
become easterly. The result is that most
of the motion is around the earth (zonal)
with less than one-tenth of the motion be-
tween poles and equator. The meridional
POLAR TROPOPAUSE
POLAR FRONT JET
TROPICAL
TROPOPAUSE
GENERAL CIRCULATION MODEL
(AFTER PALMEN)
FIGURE 2
TEMPERATURE
Variation with Height
In'the lower region, of the atmosphere ex-
tending from the surface to about 2 km.,
the temperature distribution varies consid-
erably depending upon the character of the
underlying surface and upon the radiation
at the surface. The temperature may de-
crease with height or it may actually in-
crease with height (inversion). This region
is the lower troposphere and is the region
of most interest in air pollution meteorology.
The remainder of the troposphere has a
decrease of temperature with height on the
B-104
-------
Me teor ologicF undamentals
order of 4 to 8°C per km. The stratosphere
is a region with isothermal or slight inver-
sion lapse rates. The layer of transition
between the troposphere and stratosphere
is called the tropopause. The tropopause
varies in height from about 8 to 20 km. and
is highest near the equator, lowest near the
poles. Figures 3 and 4 indicate typical
temperature variations with height for two
latitudes for summer and winter in the
troposphere and lower stratosphere.
HEIGHT
(K H.. i 10
-40 -40 -10 0
TEMPEtATUftE (°C)
VARIATION Of TEMPEIATME WITH HEIGHT AT 30" NOITH LATITUOC
FIGURE 3
(KM.)
VACATION OF TEMPHATinE WITH HEIGHT AT
-------
Meteorologic Fundamentals
Adiabatic Lapse Rate
Due to the decrease of pressure with height,
a parcel of air lifted to a higher altitude will
encounter decreased pressure and will
expand and in undergoing this expansion will
cool. If this expansion takes place without
loss or gain of heat to the parcel, the change
is adiabatic. Similarly a parcel of air forced
downward in the atmosphere will encounter
higher pressures, will contract and will be-
come warmer. This rate of cooling with
lifting or heating with descent is the dry
adiabatic process lapse rate and is 5.4°F
per 1000 feet or approximately 1° C per 100
meters. This process lapse rate is the rate
of heating or cooling of any descending or
rising parcel of air in the atmosphere and
should not be confused with the existing
temperature variation with height at any one
time, the environmental lapse rate.
Environmental or Prevailing Lapse Rate
The manner in which temperature changes
with height at any one time is the prevailing
lapse rate. This is principally a function of
the temperature of the air and of the surface
over which it is moving and the rate of exchange
of heat between the two. For example, dur-
ing clear days in midsummer the ground
will be rapidly heated by solar radiation
resulting in rapid heating of the layers of
the atmosphere nearest the surface, but
further aloft the atmosphere will remain
relatively unchanged. At night radiation
from the earth's surface cools the ground
and the air adjacent to it, resulting in only
slight decrease of temperature with height or
if surface cooling is great enough, temper-
ature will increase with height.
If the temperature decreases more rapidly
with height than the dry adiabatic lapse
rate, the air has a super-adiabatic or strong
lapse rate and the air is unstable. If a
parcel of air is forced upwards it will cool
at the adiabatic lapse rate, but will still
be warmer than the environmental air. Thus
it will continue to rise. Similarly, a parcel
which is forced downward will heat dry
adiabatically but will remain cooler than the
environment and will continue to sink.
For environmental lapse rates that decrease
with height at a rate less than the dry adia-
batic lapse rate (sub-adiabatic or weak lapse)
a lifted parcel will be cooler than the envir-
onment and will sink; a descending parcel
will be warmer than the environment and
will rise. Figure 6 shows the relative
relation between the environmental lapse
rates of super-adiabatic (strong lapse), sub-
adiabatic (weak lapse), isothermal, and
inversion with the dry adiabatic process
lapse rate as dashed lines.
\
SUPER-ADIABATIC
\
\\ \
\\SUB-ADIABATIC
\
\ \\ \
z
-------
Meteorologic Fundamentals
outgoing radiation was shown. The temper-
ature of the atmosphere is below the boiling
point of water, yet water is volatile enough
to evaporate (change from liquid to gas) or
sublimate (change from solid to gas) at
atmospheric temperatures and pressures.
Condensation or crystallization of water
vapor in the atmosphere as clouds and on
the ground as dew or frost is common-
place. Certainly, water in the form of
clouds, fog, and precipitation are familiar
elements of weather and the latter one
necessary for agriculture and supplies
of ground water.
One measure of the amount of moisture in
the air is the dew point which is the
temperature at which saturation is reached
if the air is cooled at a constant pressure
without addition or loss of moisture. In
the atmosphere, saturation frequently
occurs due to the adiabatic cooling of
lifted air parcels until the dew point for
the lower pressure is reached. Further
cooling will condense water vapor releas-
ing the heat of condensation and because
of this release of heat, cooling of ascending
saturated air does not occur at the dry
adiabatic lapse rate but at the pseudo-
adiabatic lapse rate which is a smaller
temperature decrease with height.
WINDS
Wind is nothing more than air in motion and
although it is a motion in three dimensions,
usually only the horizontal component is
considered in terms of direction and speed.
In the free atmosphere (above the effects
of the earth's friction) two forces are
important, the first, the Coriolis force, is
due to the tendency for the air to move in
a straight path while the earth rotates
underneath. The Coriolis force is at right
angles to the wind velocity, to the right
in the northern hemisphere and to the left
in the southern hemisphere, is proportional
to the wind velocity, and decreases with
latitude. The other force is the pressure
gradient force, with direction from high
to low pressure. Above the friction layer,
in regions where the lines of constant
pressure (isobars) are straight and the
latitude is greater than 20°, the two forces
are in balance (See Figure 7) and the wind
blows parallel to the isobars with low
pressure to the left. For curved isobars
the forces are not in balance, their resul-
tant producing a centripetal acceleration.
In the lowest portion of the atmosphere
frictional drag (not due to molecular fric-
tion but to eddy viscosity) slows down the
wind speed and since the Coriolis force is
proportional to the wind speed reduces the
Coriolis force. The balance of forces
under Frictional flow is shown in Figure 8.
It will be noted that under frictional flow
the wind has a component across the isobars
toward lower pressure.
PRESSURE
GRADIENT FORCE
COR
FO
GEOSTROPHIC
WIND
OLIS
RCE
FIGURE 7
LOW
PRESSURE
GRADIENT FORCE
t - 1
P - 1
FRICTION
FORCE Tj CORIOLIS
FRICTION « »« FORCE
CORIOLIS FORCE
P +
FIGURE 8
ANTICYCLONES AND CYCLONES
Migrating areas of high pressure (anticyclones)
and low pressure (cyclones) and the fronts
associated with the latter are responsible
for the day to day changes in weather that
occur over most of the mid-latitude regions
of the earth. The low pressure systems
in the atmospheric circulation are related
to perturbations along the jet stream (the
region of strongest horizontal temperature
gradient in the upper troposphere and con-
B-107.
-------
IVbteorologic Fundamentals
sequehtly the region of strongest winds)
and form along frontal surfaces separating
masses of air having different temperature
and moisture characteristics. The forma-
tion of a low pressure system is accompan-
ied by the formation of a wave on the front
consisting of a warm front and a cold
front both moving around the low in a
counterclockwise sense. The life cycle
of a typical cyclone is shown in Figure 9.
The cold front is a transition zone between
warm and cold air where the cold air is
moving in over the area previously occupied
by warm air. Cold fronts generally have
slopes from 1/50 to 1/150. Warm fronts
separate advancing warm air from retreating
cold air and have slopes on the order of 1/100
to 1/300 due to the effects of friction on the
trailing edge of the front. Figure 10
illustrates a vertical cross section though
both a warm and a cold front.
CROSS SECTION THROUGH A COLO FRONT
AND A WARM FRONT
FIGURE 10
AIR MASSES
Air masses are frequently divided by frontal
systems and are usually classified according
to the source region of their recent history.
Air masses are classified as maritime or
continental according to origin over the
ocean or land, and arctic, polar, or tropical
depending principally on the latitude of
origin. Air masses are modified by vertical
motions and by the effects of radiation upon
the surfaces over which they move.
CONDENSATION, CLOUDS, AND PRECIPI-
TATION
Condensation of water vapor upon suitable
condensation nuclei in the atmosphere causes
clouds. Large hygroscopic nuclei will con-
dense water vapor upon them even before
saturation is reached. Table 2 indicates
the relative sizes of different particles. At
below freezing temperatures supercooled
water frequently exists for few nuclei act
as crystallization nuclei. Of course, only
a small proport: in of all clouds produce rain.
It is necessary tnat the droplets increase in
B-108
-------
Meteorologic Fundamentals
size both so that they will have appreciable
fall velocity and also so that complete evap-
oration of the drop will not occur before it
reaches the ground. Table 3 indicates the
distance of fall for different size drops
before evaporation occurs. Growth of con-
densation drops into drops large enough to
fall is thought to originate with the large
condensation nuclei which grow larger as
they drop through the cloud. The presence
of an electric field in clouds generally helps
the growth into raindrops.
TABLE 2
Sizes of Particles
Particles
Small ions
Medium ions
Large ions
Aitken nuclei
Smoke, haze, dust
Size (microns)
-3
less than 10
ID'3 to 5 X ID'2
5 X 10-2 to 2 X 10"1
5 X 10-2 to 2 X 10"1
10'1to 2
Large condensation nuclei 2 X 10"* to 10
Giant condensation nuclei 1 0 to 30
Cloud or fog droplets
Drizzle drops
Raindrops
1 to 100
100 to 500
500 to 4000
TABLE 3
Distance of Fall Before Evaporation (from
Findeisen)
REFERENCES
1 Blair, T.A. and Fite, R. C. Weather
Elements, Prentice-Hall, Englewood
Cliffs, N. J. 5th ed., 1965.
2 Byers, H. R. General Meteorology, Mc-
Graw-Hill, New York, 3rd ed.,
1959.
3 Findeisen, W., Meteorol. Z., 56, 453,
1939.
4 Hewson, E. W. ; and Longley, R. W.
Meteorology, Theoretical and Applied,
Wiley, New York, 1944.
5 Houghton, H. G. "On the Annual Heat
Balance of the Northern Hemisphere, "
J. Meteorol:, J_l, 1, 1-9. Feb. 1954.
6 Palmen, E., Quart. J. Roy. Meteorol.
Soc., 77, 337. 1951.
7 Petterssen, S. Introduction to Meteoro-
logy. McGraw-Hill, New York, 2nd
ed., 1958.
8 Shulman, M. D. Climates of the United
States. Seminar on Human Biometeo-
rology. Public Health Service Pub. No.
999-AP-25. 1967.
Radius (microns)
1
10
100
1000
2500
Distance of Fall
3.3 10'4
3. 3 cm.
150 m.
42 km.
280 km.
cm.
B-109 and B-110
-------
EFFECTS OF METEOROLOGIC PARAMETERS ON TRANSPORT AND DIFFUSION
D. B. Turner*
The air pollution cycle can be considered to
consist of three phases: the release of air
pollutants at the source, the transport and
diffusion in the atmosphere, and the recep-
tion of air pollutants in reduced concen-
trations by people, plants, animals, or
inanimate objects. The influence of
meteorology is to the greatest extent during
the diffusion and transport phase. The
motions of the atmosphere which may be
highly variable in four dimensions are
responsible for the transport and diffusion
of air pollutants.
Although the distribution with time of a
cloud of pollutant material will depend on
the summation of all motions of all siz'es
and periods acting upon the cloud, it is
convenient to first consider some mean
atmospheric motions over periods on the
order of an hour.
WIND DIRECTION
Wnat effect will the mean wind direction
have on an air pollutant? If the wind direc-
tion is representative of the height at which
the pollutant is released, the mean direction
will be indicative of the direction of travel
of the pollutants. In meteorology it is
conventional to consider the wind direction
as the direction from which the wind blows,
therefore a north-west wind will move
pollutants to the south-east of the source.
WIND SPEED
The effect of wind speed is two-fold. The
wind speed will determine the travel time
from a source to a given receptor, e. g.
if a receptor is located 1000 meters down-
wind from a source and the windspeed is 5
meters /second, it will take 260 seconds
for the pollutants to travel from the source
to the receptor. The other effect of wind
speed is a dilution in the downwind direction.
If a continuous source is emitting a certain
pollutant at the rate of 10 grams/second
and the wind speed is 1 meter/second then
in a downwind length of the plume of 1 meter
will be contained 10 grams of pollutant
since 1 meter of air moves past the source
each, second. Next, consider that the
conditions of emission are the same but
the wind speed is 5 meters/second. In
this case since 5 meters of air moves
past the source each second, each meter
of plume length contains 2 grams of pollu-
tant. Therefore it can be seen that the
dilution of air pollutants released from a
source is proportional to the wind speed.
This may be restated in another form: The
concentration of air pollutants is inversely
proportional to wind speed.
VARIABILITY OF THE WIND
In the preceding paragraphs consideration
of only the mean speed and direction of
wind has been.made. Of course, there are
deviations from this mean velocity. There
are velocity components in all directions so
that there are vertical motions as well as
horizontal ones. These random motions
of widely different scales and periods are
essentially responsible for the movement
and diffusion of pollutants about the mean
downwind path. These motions can be
considered atmospheric turbulence. If
the scale of a turbulent motion i.e. the
size of an eddy, is larger than the size of
the pollutant plume in its vicinity, the eddy
will move that portion of the plume. If an
eddy is smaller than the plume its effect
will be to diffuse or spread out the plume.
This diffusion caused by the eddy motion is
widely variable in the atmosphere but even
when this diffusion is least, it is on the
order of three orders of magnitude greater
than the diffusion by molecular action alone.
MECHANICAL TURBULENCE
Mechanical turbulence is the induced eddy
structure of the atmosphere due tp the
roughness of the surface over which the air
is passing. Therefore the existance of trees,
shrubs, buildings, and terrain features will
Meteorologist, Air Resources Cincinnati
Laboratory ESSA, NAPCA, Cincinnati,
Ohio
PA. ME. mm. 14. 6. 67
B-lll
-------
Effects of Meteorologic Parameters on Transport and Diffusion
cause mechanical turbulence. The height
and spacing of the elements causing the
roughness will affect the turbulence. In
general, tho higher the roughness elements
the greater the mechanical turbulence. In
addition the mechanical turbulence increases
as wind speed increases.
THERMAL TURBULENCE
Thermal turbulence is that induced by
the stability of the atmosphere. When
the earth's surface is heated by the sun's
radiation, the lower layer of the atmos-
phere becomes unstable and thermal tur-
bulence becomes greater, expecially under
c onditions of light wind. On clear nights
with light winds, heat is radiated from the
earth's surface resulting in cooling of the
ground and air adjacent to it. This results
in extreme stability of the atmosphere near
the earth's surface. Under these con-
ditions turbulence is at a minimum.
RELATION OF TURBULENCE TO WIND
RECORDS
Attempts to relate different measures of
turbulence of the wind to atmospheric
diffusion have been made for quite some
time. Lowry (1951) related the distance
of the maximum concentration to the
standard deviation of wind direction over
.1.0 to 15 minute periods. Smith (1951) has
used a classification of wind trace types
using wind vane records as an indication
of atmospheric stability. Hay and Pasquill
(1957, 1959), Cramer (1958), and Islitzer
(1961) have all compared diffusion experi-
ment results with statistics of wind direc-
tion fluctuations in both the horizontal and
>T:rtical. Direct methods of relating wind
st-Mli.sti.es to estimates of dispersion
(Pasquill, 1961, 1962) show promise and
attempts at developing suitable instru-
mentation to yield the necessary wind
statistics directly have been made (Jones
and Pasquill, 1959).
RELATION OF TURBULENCE TO ATMOS-
PHERIC STABILITY
Relations of a more qualitative type have
been noted between atmospheric diffusion
and the stability of the atmosphere. Measure-
ment of atmospheric stability by temperature
difference measurements on a tower are
frequently utilized as an indirect measure
of turbulence, particularly where clima-
tological estimates of turbulence are desired.
Under strong lapse or super-adiabatic
conditions of temperature change with
height, strong vertical and horizontal
mixing takes place in the atmosphere con-
trasted to inversion conditions with slight
horizontal mixing but extremely limited
vertical mixing. (See the section on The
Influence of Vertical Temperature Structure
Upon'Stack Effluents)
VARIATIONS OF WIND SPEED AND DIREC-
TION WITH HEIGHT
Wind speed is generally found to increase
with height above the ground and wind diui-ec-
tion to veer (turn clockwise) with height (in
the northern hemisphere at extratropical
latitudes) due to the effects of fir- tion with
the earth's surface. The amount of these
increases in speed and veering in direction
are widely variable and to a great degree
related to the roughness of the surface and
the stability of the atmosphere.
EFFECT OF SURFACE ROUGHNESS
Consider the surface wind as measured at 10
meters compared to the wind above the in-
fluence of the earth's friction, for example
about 1000 meters. Over smooth terrain
such as the great plains or over the ocean
the speed at the surface is on the order of
0. 9 the upper wind and the degree of veering
with height on the order of 10°. (See Figure l).
Over average terrain with small changes in
elevation and with some trees and shrubs,
the surface speed is more like 4/5 of the upper
wind and the amount of veering with height
about 15° to 20°. Over rough terrain, quite
hilly or mountaneous or with numerous
buildings and vegetation, the surface speed
may be only half the speed of the upper wind
and the amount of veering with height as much
as 40° to 45°.
B-112
-------
Effects of Meteorologic Parameters on Transport and Diffusion
SMOOTH
TEIIAIN
10 METEI 1
WIND
1000 METEI
WIND
order of 1/4 to 1/3 that of the 1000 meter
wind) and the amount of veering with
height may be on the order of 40° to 45°.
Figure 2 shows the diurnal variation of
wind speed at two different levels on a
meteorological tower (Singer and Raynor,
1957).
AVEIAGE
TEIIAIN
1000 METED
WIND
10 METE*1
WIND
iOUGH
TEIIAIN
1000 METEI
WIND
10 METE*
WIND
EFFECT OF IOUGHNESS ON
VAIIATION Of WIN3 WITH HEIGHT
FIGURE 1
DIURNAL VARIATION
During the daytime, solar heating causes
turbulence to be at a maximum and ver-
tical motions to be strongest. This causes
the maximum amount of momentum ex-
change between various levels in the at-
mosphere. Because of this, the variation
of wind speed with height is least during
the daytime. Also the amount of veering
with height is least (on the order of 15° to
2QO over average terrain). The thickness
of the friction layer will also be greatest
during the day due to the vertical exchange.
At night the vertical motions are least and
the effect of friction is not felt through as
deep as a layer as during the day. The
surface speed over average terrain is much
less than the free atmosphere wind (on the
WIND
SPEED
(M/SEQ
SUNRISE MIDDAY SUNSET MIDNIGHT SUNRISE
DIURNAL VARIATION OF WIND SPEED
Data from Meteorological Tower
Breokhovcn National laboratory
April 1930-Morch 1952
FIGURE 2
FRONTAL TRAPPING
Since frontal systems are accompanied by
inversions, trapping of air pollution beneath
these inversions can occur. These may allow
relatively high concentrations. Frontal
trapping may occur with either warm fronts
or cold fronts. Since warm fronts are usually
slower moving and also the frontal surface
slopes more gradually than that of a cold
front, trapping will generally be more im-
portant with warm fronts. In addition the
low level and surface wind speeds ahead of
a warm front - within the trapped sector -
will usually be lower than the wind speeds
behind a cold front. Because of the orienta-
tion of frontal systems with respect to low
pressure systems in the Northern hemisphere,
most surface winds associated with cold
fronts are from the quadrant west through-
north and winds associated with warm fronts
are from the east through south quadrant.
Therefore most warm frontal trapping will
occur to the west through north from a given
source and cold frontal trapping to the east
through south of the source.
B-113
-------
Effects of Meteorologic Parameters on Transport and Diffusion
REFERENCES
Cramer, H. E.; Record, F. A.; and Vaughan,
H. C. "The Study of the Diffusion of
Gases or Aerosols in the Lower Atmos-
phere", Final Report, Contract No.
AF 19(604)-1053, 1.5 May 58, Mass.
Inst. of Tech., Dept. of Meteorol.
Hay, J. S.; and Pasquill, F. "Diffusion
from a Fixed Source at a Height of a Few
Hundred Feet in the Atmosphere", J. of
Fluid Mech., 2, 3, 299-310, May, 1957.
Hay, J. S.; and Pasquill, F. "Diffusion
from a Continuous Source in Relation
to the Spectrum and Scale of Turbulence",
in Atmospheric Diffusion arid Air Pollu-
tion, Frenkiel, F. N.; and Sheppard, P. A.,
editors, Academic Pross, London, 1959.
Islitzer, Norman.F. "Short-Range Atmos-
pheric Dispersion Measurements from
an Elevated Source", J. Meteorol., 18.
4, 443-450, August 1961.
Jones, J. I. P.; and Pasquill, F. "An
Experimental System for Directly Re-
cording Statistics of the Intensity of
Atmospheric Turbulence", Quar. J.
of the Roy. Meteorol. Soc., 85, 225-236,
1959.
Lowry, P. H. "Microclimate Factors in
Smoke Pollution From Tail Stacks ",
in: On Atmospheric Pollution, Meteorol.
Mono. 1, 4, 24-29, Nov. 1951.
Pasquill, F. "The Estimation of the Dis-
persion of Windborne Material, " The
Meteorol. Mag., 90, 1063, 33-49,
Feb. 1961.
Pasquill, F. Atmospheric Diffusion. Van
Nostrand, London, 1962.
Singer, I. A.; and Raynor, G. S. "Analysis
of Meteorological Tower Data, April
1950 - March 1952, Brookhaven National
Laboratory", AFCRC TR-57-220,
Brookhaven National Laboratory,
June 1957.
Smith, M. E. 'The Forecasting of Micro-
meteorological Variables", in: On
Atmospheric Pollution, Meteorol. Mono.,
1. 4, 50-55, Nov. 1951.
B-114
-------
POLLUTANT CONCENTRATION VARIATION
D. B. Turner*
THE INFLUENCE OF VERTICAL TEMPER-
ATURE STRUCTURE UPON STACK EFFLU-
ENTS
The manner in which stack effluents diffuse
is primarily a function of the stability of
the atmosphere. Church (1949) has typed
the behavior of smoke plumes into five classes.
Hewson (1960) has added a sixth class taking
into account inversions aloft.
LOOPING
Looping occurs with a superadlabatic lapse
rate. Large thermal eddies are developed
in the unstable air and high concentrations
may be brought to the ground for short time
intervals. Diffusion is good however when
considering longer time periods. The
superadiabatic conditions causing looping
occurs only with light winds and strong solar
heating. Cloudiness or high winds will
prevent such unstable conditions from forming.
CONING
With vertical temperature gradient between
dry adiabatic and isothermal, slight instability
occurs with both horizontal and vertical
mixing but not as intense as in the looping
situation. The plume tends to be cone shaped
hence the name. The plume reaches the
ground at greater distances than with looping.
Coning is prevalent on cloudy or windy days
or nights. Diffusion equations are more
successful in calculating concentrations for
this type of plume than for any other.
FANNING
If the temperature increases upward the air is
stable and vertical turbulence is suppressed.
Horizontal mixing is not as great as in coning
but still occurs. The plume will therefore
spread horizontally but little if any vertically.
Since the winds are usually light the plume
will also meander in the horizontal. Plume
concentrations are high but little effluent from
elevated sources reaches the ground with this
situation except when the inversion is broken
due to surface heating, or terrain at the
elevation of the plume is encountered.
Clear skies with light winds during the
night are favorable conditions for fanning.
LOFTING
Lofting occurs when there is a superadia-
batic layer above a surface inversion.
Under this condition diffusion is rapid up-
ward but downward diffusion does not
penetrate the inversion and so is damped
out. With these conditions gases will not
reach the surface but particles with
appreciable settling velocities will drop
through the inversion. Near sunset on a
clear evening in open country is most favor-
able for lofting. Lofting is generally a
transition situation and as the inversion
deepens is replaced by fanning.
FUMIGATION
As solar heating increases the lower layers
are heated and a super-adiabatic lapse rate
occurs through a deeper and deeper layer.
When the layer is deep enough to reach
the fanning plume, thermal turbulence will
bring high concentrations to the ground
along the full length of the plume. This
is favored by clear skies and light winds and
is apt to occur more frequently in summer
due to increased heating.
Another type of fumigation may occur in the
early evening over cities. Heat sources
and mechanical turbulence due to surface
roughness causes a lapse condition in the
lower layers of the stable air moving into
the city from non-urban areas where
radiation inversions are already forming.
This causes a fumigation until the city loses
enough heat so that the lapse condition can
no longer be maintained.
TRAPPING
When an inversion occurs aloft such as a
frontal or subsidence inversion a plume
released beneath the inversion will be trapped
beneath it. Even if the diffusion is good
beneath the inversion such as a coning plume.
Meteorologist, Air Resources Cincinnati
Laboratory ESSA, NAPCA, Cincinnati,
Ohio
PA. ME. sd. 30a. 8. 62
B-115
-------
Pollutant Concentration Variation
the limit to upward diffusion will increase
concentration in the plume and at ground
level.
The six plume classes are diagrammed in
the accompanying figure.
t
c
o
O
c
o
u
I I I I I _ I _ I _ I 1 I I
00 02 04 U Ot 10 II 14 It IS 20 12 M
tEMKlATUU DISTANCE DOWNWIND
', Mt ADIADATIC 1AKC HATE
VARIATION OF POLLUTANT CONCENTRA-
TIONS DUE TO METEOROLOGIC VARIATIONS
An example of the diurnal variation of
pollutant concentrations is given in this
figure. These are the concentrations
some distance down-wind from a contin-
uous elevated urban source on a day when
stability reaches extremes, i. e. , on a
clear day with light winds. This shows
only the variations on the order of an
hour's duration rather than the rapid vari-
ations which may occur a few minutes
duration.
The primary maximum around 10 AM is
due to fumigation. The rapid decrease in
concentration following this is due to the
heating of a progressively deeper layer
and mixing of pollutants through this layer.
Diurnal Variations of Ground-Level Concen
trations from Elevated Urban Sources
The increase of concentrations during the
late afternoon are due to the slight increase
in stability after the period of maximum
heating. During this period the lapse
rate is generally changing from strong
lapse to weak lapse.
The secondary maximum that occurs in
the evening is a phenomena observed only
in the urban area. During the late afternoon
and ear'y evening a radiation inversion
begins to form at the earth's surface in the
non-urban areas, i. e., tha surrounding
countryside. The air over the city, how-
ever, does not have a radiation inversion
in the lower layers due to release of heat
from the buildings and pavings of the city.
However, later in the evening, an inversion
above the weak lapse layer forms above the
city and a mixing of the pollutants in thia
layer produces the higher concentrations.
This has been described by Munu and K.'atz
(1959). Hewson (I960) refers to this as a
"Type II Fumigation".
When the base of this inversion aloft lowers
enough so that the elevated emissions are
into the inversion layer the concentrations
decrease and continue to decrease until
after sunrise. Then surface heating is
sufficient to produce mixing beneath the
inversion and pollution previously.in the
inversion layer is mixed through the layer
of super-adiabatic lapse rate beneath the
remaining upper portion of the inversion
resulting in high ground level concentrations.
B-116
-------
Pollutant Concentration Variation
REFERENCES
1. Church, P. E. ; "Dilution of Waste Stack
Gases in the Atmosphere", Ind. Eng.
Chem. 41, 12, 2753-2756, Dec. 1949
2. Hewson, E. W. ; "Meteorological Measuring
Techniques and Methods for Air Pollution
Studies" in Industrial Hygiene an Toxi-
Cology, Vol. 3. L. Silverman (Ed. )
New York, Interscience
3. Munn, R. E. and Katz, M. "Daily and
Seasonal Pollution Cycles in the Detroit
Windsor Area". Int. J. Air Poll.,2.1.
51-76, July 1959.
B-117 and B-118
-------
LEGAL ASPECTS OF AIR POLLUTION
H. C. Crowe*
I INTRODUCTION
Man has always required a mechanism to
regulate his actions with his fellowman.
This regulation has resulted in the formation
of laws. A law is simply defined as a rule
of human conduct that will be enforced by
the State through its public tribunals or
officers. In this respect, air pollution re-
quires regulation much like every other
action of man. The development of air pollu-
tion law is in its infancy and as the need for
Air Pollution legislation grows, the enact-
ment of specific legislation to abate and
control air pollution is slowly evolving
across the nation. The Air tyiality Act
Act of 1967 has given the necessary impetus
to the drafting of more specific legislation
and as the state of the art grows, there will
be many more stringent laws to abate air
pollution problems.
II LEGAL ASPECTS
The legal aspects of air pollution may be
categorized under the three headings of
apprehension, trial and penalty.
A Apprehension
Involves not only the citing of a source
owner for violation of an air pollution
law, but examines the origin and content
of the law under which the source owner
was cited.
The enacting legislative body may have
lacked constitutional authority, at the
Federal or State level, to have passed
the legislation; hence the law will not
stand. The law may have been written
in an unrealistic, capricious or arbitrary
manner, again the law will not stand.
The citing officer may not have been
duly authorized to issue the citation,
again the case would be removed from court.
B Trial
The trial, whether it is before the hearing
board of an administrative agency or a
court of law, is that part of the legal
process that allows both parties, the de-
fendant and prosecutor, to plead their
case. Each party has the right to intro-
duce such evidence that will help his
case. The loser of the case has the right
to appeal the decision to a higher court.
The introduction of evidence and initiation
of an appeal must follow certain well
defined procedures. In any event the
case is decided upon the facts in an im-
partial manner, according to established
legal doctrines.
C Penalty
The penalty imposed should be one that
will abate air pollution in the most effec-
tive manner. The penalty could be based
upon:
1 Nuisance
2 Criminal code
3 Civil injunction
4 Combination of criminal code and
civil injunction
III THE ORIGIN OF LAW
Law may be divided into two categories,
the common law or stare decisis and the
statute law. Since most of our law has
evolved from the English Common Law, we
see that this law has evolved through the
growth of the British Empire and reflects
the attempt of the early English Kings to secure
monetary payment for wrongs done against
the royalty of the early English courts. This
common law is based upon fitting the facts
at hand into previous cases and deciding the
PA.A.le.l3a.9.69
* Chief, Special Training Branch,
Training Institute, U. S. Department
of Health, Education, and Welfare
Environmental Control Administration,
Cincinnati, Ohio
B-119
-------
Legal Aspects of Air Pollution
current case on a basis of previous decisions.
Statute law is legislation enacted by an
authorized body to facilitate the bringing to
trial of various offenders instead of reviewing
the previous history on cases of this type.
Violation of a statute is prima facie evidence
of the commission of a wrongful act. This
method of trial usually results in swifter
court action and the decision is often more
equitable to both parties. The statute law
is based upon the common law but in the
event that statute law does not directly fit the
facts at hand, the common law is relied upon
to secure justice.
A Sources of. Law
The United States Constitution guarantees
that the rights of the individual states
shall be supreme and all rights assigned
to these states are to be enforced by the
states. Certain rights are granted to the
Federal Government. Those rights
going to the Federal Government involve
either interstate, international problems,
or those problems that pertain to the wel-
fare of all of the peoples of the United
States. State rights are applied to any
individual action that affects the people
within this state. The state, in its
supreme position, can grant the Federal
Government certain powers. The state
may also grant the local governments,
city or county, certain powers. The
state governments however retain the
right to discharge or cancel powers which
they grant. This is the basis by which a
state may enact enabling legislation to
create an administrative agency to abate
air pollution.
IV APPLICATIONS OF LAWS
The applications of law to the field of air
pollution originates basically with the State
Health Department code. From this point,
the enabling legislation is enacted by the
State Legislature so that local governments
may have the ability to enact air pollution
legislation either in the local health depart-
ment or in a separate agency. The problem
then becomes what criteria will be used to
determine whether to establish a separate
air pollution agency or to maintain an air
pollution section in the local health depart-
ment. If the air pollution problem for a given
geographical area is severe, the public
is sufficiently aroused and the local courts
are receptive, then the establishing of an
air pollution control agency appears to be
the answer. Where the air pollution prob-
lem is not so severe and the public is not
aware of the problem, and the courts are
not receptive, then the establishing of an air
pollution section in the health department
seems to be the answer. The problem is
always defining whether the problem is
severe and whether the public is aware of the
problem, and whether the courts are recep-
tive to the people that are administering the
program. In any event, an air pollution
officer is appointed. In the administrative
agency, hearing boards are established for
the trying of cases. These hearing boards
function as a court and the functions of
administrative law are used as a basis for
deciding the cases. The decisions of these
boards may be appealed to an appellate court
of law and if these original decisions are
found to be unrealistic, capricious, or
arbitrary, they may be reserved by the
appellate court.
The air pollution section in the health
department operates in much the same
fashion except the case originates in a court
of law. The decision of these courts may be
referred to an appellate court and again if
they have been found to be unrealistic, cap-
ricious, or arbitrary, the decisions of the
lower court may be overturned.
A The local agency must determine whether
it wishes to abate or control air pollution.
The penalty it envokes is a direct function
of that which it wishes to accomplish
abatement, or control. There are four
bases for achieving this abatement of
air pollution:
1 Nuisance
2 Criminal code
3 Civil injunction
B-120
-------
Legal Aspects of Air Pollution
4 A combination of criminal code and
civil injunction
Penalty under a nuisance law is usually
payment of a monetary fine, a holdover
from the early English Common Law.
This involves paying a fine after the act
has been committed. Under the criminal
code, the action is declared a misdemeanor
and may be either satisfied by a monetary
fine or imprisonment for a given length
of time. The civil injunctive proceeding
allows the courts to declare an act against
public policy and prohibits the source
owner from continuing with that activity.
The weakness of the nuisance law is that
monetary damages, after an act has been
done, will not abate air pollution nor
does paying a monetary fine under the
criminal code or possible imprisonment
stop a source owner from continuing with
his illegal practice. It is possible for
the violator to set aside a certain amount
of budget for the necessary fines or assign
one man to spend sufficient time in jail
to satisfy the imprisonment penalty. The
civil injunction appears to be a better way
to abate air pollution. A problem resulting
is that a small manufacturing source can-
not allow itself to be closed down for even
a short period of time. Therefore, the
penalty becomes unrealistic with re.spect
to the act that was committed. It requires
extensive time and legal manipulations
to secure an injunction against a source
owner but once secured, can be used
effectively against a large source owner.
The combination of the criminal code and
civil injunctive proceedings offers a more
equitable approach to the abatement of
air pollution for the small source owner
and for the large source owner. A fine
under the criminal code may be sufficient
to bring the small operator into line with
the air pollution law and the threat of
plant shutdown may be all that is necessary
to bring the large source owner into com-
pliance with the local air pollution laws.
The choice of penalty mechanism is de-
pendent upon the extent of the problem in
that'specific geographic area. The ability
of the local agency to enforce the laws
and the receptivity of the courts or the
hearing boards, in the case of an admin-
istrative agency, also determines the
correct penalty mechanism that will
effectively achieve the goal of "clean air".
V SUMMARY
The effectiveness of an air pollution control
agency's program is dependent upon the type
of law that the agency employs. Common
law may be sufficient for a small agency
with a minor air pollution problem, but
statute law may be required for an agency
that has a large abatement problem.
Any law that is enacted must be constitu-
tional. Any air pollution law cannot
be contrary to the Federal Constitution or
the State Constitution, and any governing
body enacting air pollution legislation must
have the constitutional requirements for
enacting such legislation. In any event,
the law that is employed must be specifically
tailored for the problems of the area. In-
telligent administration and enforcement
of the local air pollution law becomes a
major factor in the abating of the air pollu-
tion problem.
REFERENCES
1 Prosser, W. C. Law of Torts, 3rd Edi-
tion 1964, West Publishing Co., St.
Pau], Minn., pp 592-633.
2 Pluckwett, T. F. A Concise History
of the Common Law. Layers Co-
Operative Publishing Co.
3 Kennedy, H. W. Fifty Years of Air
Pollution Law. JAPCA Vol. 7,
pp 125-139, August 1957.
4 Kennedy, H. W. Legal Aspects of Air
Pollution Control. Public Health Re-
ports. Vol. 19, pp 689-95, August
1964.
5 Grad, F. P. Public Health Law Manual.
American Public Health Association,
1965.
6 Juergensmeyer, J.C., "Control of Air
Pollution Through Assertion of
Private Rights", Duke Law Journal,
December 1969, p. 1126.
B-121 and B-122
-------
TECHNIQUES FOR VISUAL DETERMINATION
D. P. Holzschuh*
I Introduction
Visible devices are used to measure the in-
tensity of black smoke from a single source
by comparison to shades of gray. They are
not meant for use in the measurement of
smoke of any other color. These devices
were designed along practical lines rather
than theoretical concepts.
II Ringelmann System
A A device whereby graduated shades of gray,
varying by five equal steps between white
and black, may be accurately reproduced.
A rectangular grill containing black lines
of definite width and spacing on a white
background is used.
B Specifications for the reproduction of the
chart are as follows:
Card 0 - all white (100% of light trans-
mitted)
Card 1 - black lines 1 mm thick, 10 mm
apart, leaving white spaces 9 mm
square (80% transmission)
Card 2 - lines 2.3 mm thick, spaces 6.3 mm
square (60% transmission)
Card 3 - lines 3.7 mm thick, spaces 6.3 mm
square (40% transmission)
Card It - lines 5.5 mm thick, spaces 4.5 mm
square (20% transmission)
Card 5 - all black (0% transmission)
This chart, as distributed by the U. S.
Bureau of Mines, provides the shades of
Cards 1, 2, 3, and 4 on a single sheet,
which are known as Ringelmann No. 1, 2, 3
and 4 respectively.
C Use of the Chart
1 It is supported at eye level, at such
a distance from the observer that the
lines on the chart merge into shades
of gray. The observer should- be a
distance of between 100 feet and 1/4
mile from the source.
*Physical Science Technician, NAPCA
PA.FA.pm.45a.10.69
The observer notes the intensity of
smoke issuing from the source, and
records the chart number corresponding
to the shade of intensity, and also
records the time of observation.
Observations are repeated at one-quarter
or one-half minute intervals. The read-
ings are then reduced to the total equiv-
alent of No. 1 smoke as a standard. Be-
cause No. 1 smoke is 20% dense, the
percentage density of the smoke for the
entire period of observations is obtained
by this formula:
Equivalent units of No. 1 smoke * 20%
Number of observations
percentage smoke density.
4 Example
Between the hours of 10:00 and 11:00 A.M.,
the following readings were taken at one-
quarter minute intervals.
No. of
Readings
7
7
27
34
52
113
Ringelmann
No.
5
4
3
2
1
0
Equivalent
No. /units
35
28
81
68
52
0
240
264
Smoke Density
264 * 20
240
22%
D Experienced observers find it unnecessary
to continue to refer to the chart.
E This method seems likely to remain in
practice because Its use is specified in
most legal codes.
B-123
-------
Techniques For Visual Determination
F The following factors may effect the read-
ing obtained by the Ringelmann method:
1 Diameter of the stack
2 Cloud and wind conditions
3 Position of the sun relative to the
observer
4 Human element in judging shades of gray
5 The need to refocus the eyes from the
stack plume to the chart.
6 The purpose of the Ringelmann system
is not to find violators but to lessen
smoke emissions and to obtain better
cooperation in establishing a cleaner
community. It is a reasonable and
economical method of obtaining compli-
ance for industry.
H .The Ringelmann system, at this time, pro-
vides no means for correlating its number
to total particulate or grain loading which
is applicable to all sources.
Ill Smokescope
A The smokescope was developed by the Mine
Safety Appliance Company. It was designed
to overcome some of the disadvantages of
the Ringelmann chart.
B Principle of Operation
1 The observer views tlie stack through the
instrument, aiming it so that smoke
fills the field of vision through aper-
tures C, D, and G. Light from an area
adjacent to the stack is transmitted
through the reference disc, H, in
barrel, B, to the surface of mirror E.
From this mirror, an image of the re-
ference disc is projected through
lens, F, onto the image mirror where it
may be compared with the smoke seen
through the apertures.
2 The reference film is located exactly
at the focal point of the lens so that
light rays reaching the eye from the
film are parallel, making the apparent
focal distance of the virtual image in-
finity. Thus, the image can be com-
pared with the observed smoke without
refocusing the eye.
One-half of the density disc is equiv-
alent to No. 2 Ringelmann and the other
half is equivalent to No. 3 Ringelmann.
The smokescope was designed to overcome the
following disadvantages of the Ringelmann
chart.
Glass ( image mirror )
Opaque disk
Mirror
Smoke plume
Image seen in Smokescope
Figure 1. SCHEMATIC DIAGRAM OF SMOKESCOPE
B-124
-------
Techniques For Visual Determination
1 Errors in reading due to:
a Variations in the background against
which the smoke is viewed.
b Variations in the ambient light
which illuminates the charts and
which may be considerably different
from the light in the area of the
stack.
The limitations of the human eye to
refocus in glancing from the smoke
to the charts.
The main disadvantage of the smoke-
scope is its limiting the observer
to only two readings on the Ringel-
mann scale.
REFERENCES
1 Air Pollution Handbook. McGraw-Hill Book
Co., New York, 1956.
2 Encyclopedia of Industrial Hygiene,
University of Michigan Institute of
Industrial Health, Ann Arbor, Michigan.
3 Kudlich, Rudolf, Ringelmann Smoke Chart,
Bureau of Mines Information Circular
7718, U. S. Dept. of the Interior.
August, 1955.
4 Marks, L. S. "Inadequacy of the Ringelmann
Chart," Mech. Engr. 59:681-685, 1937.
5 Revised Bureau of Mines Circular 8333,
Ringelmann Smoke Chart. 'U. S. Depart-
ment of the Interior, May, 1967.
B-125 and B-126
-------
READING VISIBLE EMISSION
Jerome J. Rom*
I. THE RINGELMANN CHART AND
EQUIVALENT OPACITY
Introduction
One of the first aids devised to measure emis-
sions to the atmosphere was the Ringelmann
ChartC' (Figure 1). This was developed by
Maximilian Ringelmann in the late 1800's and has
been a useful tool ever since, at least in control-
ling visible emissions, which constitutes the
nuisance form of air pollution.
Use of Chart
Many municipal, state, and federal regulations
prescribe smoke-density limits based on the
Ringelmann Smoke Chart, as published by the
Bureau of Mines. Although the chart was not
originally designed for regulatory purposes, it is
presently used for this purpose in many juris-
dictions where the results obtained are accepted
as legal evidence.
Equivalent Opacity
Although the Ringelmann Chart is only useful in
evaluating black or gray emissions, a principle
of equivalent opacity was developed later which
makes possible the application of the Ringelmann
principle to other colors of smoke. Ordinances
limiting equivalent opacity merely limit the visi-
ble emission of such opacity as to obscure an
observer's view to a degree equal to or greater
than the equivalent Ringelmann number. Opacity
simply means the degree to which transmitted
light is obscured.
Below is the relationship between Ringelmann
number and opacity:
Opacity %
20
40
60
80
100
Ringelmann No.
1
2
3
4
5
Smoke Readings Aids
Although a number of smoke readings aids have
been developed to assist in measuring the
Ringelmann number of gray or black smoke,
none have the versatility of a trained inspector
under varying conditions. Some of these devices,
however, are very useful in the initial training
of an inspector. Devices designed to aid in
smoke reading include the smokescope, smoke
tintometer, umbrascope, and various charts and
film strips. The smokescope uses a film disc
for comparison, while the smoke tintometer and
umbrascope use tinted glass. The various smoke
charts developed work on the Ringelmann princi-
ple, comparing shades of gray with the source
emission. A film strip comprising four densi-
ties of film of 80, 60, 40, and 20% transmission
for comparison with the source emission has been
developed by the Public Health Service and identi-
fied as a Smoke Inspection Guide' '. The inspec-
tor simply views the source through the film strip
and matches it as closely as possible with one of
the densities on the guide.
Many permanently installed devices are com-
mercially available to continuously monitor and
record the emissions. Some are designed to set
off an alarm when the emissions reach a preset
level and to warn operating personnel. Most of
these devices use the light source-photocell com-
bination to measure the transmission of light
through the plume or remove a sample of the
plume and measure the transmission of light
through this sample.
The main problem with most of these devices is
in trying to periodically zero the photocell, at
least in a continuous operation where the emis-
sion must be stopped to obtain a true zero. Emis-
sion build-up on the light source and photocell
also poses a problem. Some of these devices
draw a portion of the emission from the source
for measurement. With these it is difficult to
obtain a truly representative sample from the
source, especially if conditions vary. However,
the problems of zeroing the instrument is elimi-
nated by this method.
Use of Visible Plume
Evaluation Techniques
Many laws governing air pollution now contain
restrictions as to the Ringelmann number a
source may emit, and most of the latest laws are
incorporating the limits in terms of equivalent
opacity also, so as to cover every type of visible
emission. An example of such a law is that
written by the Air Pollution Control District,
County of Los Angeles and quoted below:
Rule 50. Ringelmann Chart. A person shall not
discharge into the atmosphere from any single
source of emission whatsoever any air contami-
nant for a period or periods aggregating more
than three minutes in any.one hour which is:
*Office of Air Programs, EPA
B-127
-------
Ringelmann Chart and Equivalent Opacity
1. Equivalent to 20 percent black.
2. Equivalent to 40 percent black.
3. Equivalent to 60 percent black.
4. Equivalent to 80 percent black.
Figure 1.
RINGELMANN'S SCALE FOR GRADING THE DENSITY OF SMOKE
B-128
-------
'Ringelmann Chart and Equivalent Opacity
(a) As dark or darker as that designated
as No. 2 on the Ringelmann Chart, as
published by the United States Bureau
of Mines, or
(b) Of such opacity as to obscure an
observer's view to a degree equal to
or greater than does smoke described
in subsection (a) of this rule'^).
Enforcement of this type regulation is simple and
straightforward. All that is needed is a trained
inspector's observation record (Figure 2) that
the plume exceeded the cut-off point and time
interval allowed, and the violator may be cited
for excessive smoke. With these laws, and
trained personnel, much can be accomplished in
the area of abating and controlling air pollution.
It follows that if visible emissions are reduced,
the contamination of the air is also going to be
reduced.
Costs
The use of the Ringelmann Chart and equivalent
opacity principle is within the means available
to state and municipal health and air pollution
agencies, since the cost is normally only that of
training existing personnel. Afte r the initial
intensive training of 24-32 hours, only about
24 hours per year are necessary to test and
refresh personnel in the techniques of evaluating
plumes. An efficient portable smoke generator
can be built or purchased commercially for about
$3500 and the operation of it is very inexpensive,
about $1. 50 per hour. Besides this, many
smoke reading courses are now being offered
throughout the country by various municipal,
state, and federal agencies. Most of these
courses are open to enforcement personnel at a
very nominal charge or no charge whatsoever.
Once trained and qualified, one inspector can
make many observations in one day. A particu-
late source test takes a minimum of one day for
testing plus the time needed for laboratory analy-
sis and report writing at a minimum cost of
$1,000 per source. While it is not feasible, be-
cause of cost and time, to test every available
source, it is possible to evaluate each source
many times by visible observation. An inspec-
tor can normally choose a vantage point where
he can view more than one source at one time.
Also these sources can be evaluated under vary-
ing operating conditions, while a source test is
only valid for the conditions in force at the time
of sampling.
LEGAL FOUNDATION FOR RINGELMANN
CHARTS AND EQUIVALENT OPACITY
REGULATION
General Discussion of Legal Principles
Involved
With proper training under varying conditions, an
inspector can evaluate plumes within an average
deviation of not more than 10% and generally
closer to 5%. In light of this capability the courts
have upheld the Ringelmann and Opacity principles
when used by qualified personnel with good judg-
ment. To fulfill the requirements for court
testimony, it is necessary to have accurate
records of the inspector's readings on the smoke
generator to offer as evidence of his qualifica-
tions. Also, it is necessary to have an accurate
and complete record of his readings at the source
of complaint, as well as supportive data on sky
conditions, wind speed and direction, and general
meteorological conditions (Figure 2) during the
time the source was observed.
Actual Court Cases
1. People versus Plywood Manufacturers
of California'4'
2. People versus International Steel
Corporation^-''
Both of the above cases challenged the constitu-
tionality of Section 24242 of the California Health
and Safety C°de and the reliability of the Ringel-
mann number and equivalent opacity principle.
The court decided the following:
1. The Code is constitutional.
2. Opacity is neither "mystic nor incom-
prehensible. " In simple terms, it con-
demns smoke or any other contaminant
that is at least as dark or darker than
Ringelmann No. 2.
3. Even though the ordinary person cannot
tell whether his smoke is in violation,
this is no reason for the unconstitution-
ality of the law.
4. The scientific facts of the above code
are commonly recognized and well
established.
5. It is permissible for a statute to refer
to and adopt, for description of a pro-
hibited act, an official publication of any
United States board or bureau estab-
lished by law.
B-129
-------
Figure 2
NATIONAL CENTER FOR AIR POLLUTION CONTROL
PLUME OBSERVATION RECORD FORM
Date
Observer
Checked by
Start Time 9:00 AM
Observation point
Stack-distance from tit.
Wind-speed Direct.
Sky condition
Type of Installation
Fuel
Observ. Ended 10:00 AM
Smoke Density Tabulation
No. Units X Equlv. No. 1
Units
113 Units No. 0 0
Units No. 1/2
52 Units No. 1 52
Units No. 1-1/2
34 Units No. 2 68
Units No. 2-1/2
27 Units No. 3 81
Units No. 3-1/2
7 Units No. 4 28
Units No. 4-1/2
7 Units No. 5 35
140 Total Units
Total Equiv. No. 1 Units
264
Aver. Smoke Density «
Equiv. No. 1 Units X 20%
Total Units
. 22%
Remarks:
\Sec.
Min7\
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
Source location
Address
0
--
_.
--
1
1
2
2
3
2
1
--
--
--
--
._
--
_.
2
2
2
3
3
4
5
4
3
2
1
15
--
___
_.
1
1
2
3
3
2
1
--
--
--
--
--
--
--
--
2
2
2
3
4
5
5
4
3
2
1
30
>.
_.
-.
1
1
2
3
3
1
--
--
--
--
--
--
--
2
2
2
3
4
5
5
3
3
1
1
45
..
__
--
1
1
2
3
3
1
--
--
--
~-
_.
--
2
2
2
3
4
5
5
3
3
1
1
^Sec.
Mi>^
30
31
32
3.3
34
35
36
37
38
39
40
41
32
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
0
1
1
--
--
--
1
1
1
1
--
--
--
1
2
3
3
2
2
2
1
1
--
--
--
--
15
1
1
__
-
-.
1
1
1
1
--
'--
--
--
1
2
3
3
2
2
1
1
1 ,
--
--
--
--
30
1
1
__
--
__
1
1
1
--
--
--
__
...
2
3
3
4
2
2
1
1
1
--
--
--
--
--
45
1
1
__
__
__
1
1
1
--
--
--
--
--
--
2
3
3
3
2
2
1
1
--
--
--
--
--
--
B-130
-------
Ringelmann Chart and Equivalent Opacity
6. The drawing of a line between per-
mission and prohibition is a matter of
legislative discretion which will not be
reversed by the courts unless abused.
7. An inspector need not have a Ringel-
mann Chart in his possession while
observing plumes.
8. If the plume, fairly viewed from any
position, exceeds the limit, it is in
violation.
III. FLUME EVALUATION SCHOOL
A typical example of the contents and conduction
of a plume evaluation school is given below.
Training Personnel
1. Discussion of Theory
Explanation of the Ringclmann Chart and
Equivalent Opacity principle introduces an
inspector to a plume evaluation course.
After a thorough understanding of the
theory involved, lectures are presented on
the principles of combustion, burning of
various types of fuel, legal aspects of
visible emission evaluation, and smoke
reading and recording techniques.
2. Smoke Reading Form (Figure 3)
Numbers 1 through 4 are self explantory.
Number 5 - Observer's Position - in
relation to the sun, smoke generator,
and plume.
Number 6 - Instructor's or examiner's
name.
Run Number - The run number with the
suffix "B" for black smoke of "W" for
white smoke.
Observer Reading - entered by the ob-
server when the horn sounds.
Transmissomctcr Reading - True reading
from transmissometcr.
+ Deviation If the observer's reading is
greater than the transmissometer reading.
- Deviation - If the observer's reading is
less than the transmissometer reading.
Number 7 - Enter run number.
Number 8 - Enter number correct.
Number 9 - Enter number of plus
deviations.
Number 10 - Enter number of minus
deviations.
Number 1 1 - Total of plus deviations
divided by the number of plus deviations.
Example from Figure 3. = 10 = 6. 7
Number 12 - Total of minus deviations
divided by the number of minus deviations.
Example from Figure 3. = 1 0 -6.4
Number 13 - Total of plus deviations plus
the absolute value of minus deviations
divided by the total number of readings.
10 + 150
Example from Figure 3.
25
=6.4
= 3.6
Number 14' - Total number of readings
20% deviation and over. Enter all devia-
tions as percents.
Construction and Operation
of Smoke Generator
1. General Construction Features
In order to train personnel to read smoke,
it is necessary to have a unit which will
produce both black and white smoke and an
instrument to measure the transmission of
light through this smoke. For this purpose
the smoke generator was developed. The
unit currently in use for training personnel
is now. available commercially. This
generator is mounted on a boat trailer for
portability.
a. Black Smoke System (Figure 4)
Black Smoke is created by burning
benzene in a refractory-lined,
twelve cubic foot steel combustion
chamber. Incomplete combustion is
accomplished by introducing suf-
ficient excess air. Density of the
smoke is varied by adjusting the
fuel injection rate. A secondary
chamber is provided for further gas
cooling. An induced-draft fan pro-
vides adequate plume exit velocity.
This system is capable of produc-
ing black smoke from zero to num-
ber five Ringelmann'"'.
B-131
-------
Figure 3
NATIONAL CENTER FOR AIR POLLUTION CONTROL
Durham, North Carolina
SMOKE SCHOOL TRAINING FORM
1. Name of Observer.
2. Affilltation.
3. Date
Time.
4. Wind Speed.
Direction.
Sky Condition.
5. Observers Position.
6. Corrected By
(Record Black of Gray Smoke in Ringelmann No. - 1/4 Unit Smallest Division)
(Record All Other Smoke in % Opacity - 5% Smallest Division)
RUN NO. 1 B
d
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Ot
c
D
a
1
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2
2 2 1/2
3
4
5
6
7
8
9
10
11
12
T
1
I1
3
3 1/2
4
1 3/4 2
1/2
1/4
1
2
3
3 1/4
4
4 3/4
1
1/2
1 1/2
2 1/2
3
3 1/2
4
5
c
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4
c
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IT
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1
20
20
20
5
10
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10
10
5
5
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a;
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'
-------
Figure 4
TRANSMISSOMETER
COMBUSTION CHAMBER
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V.
OILUTK
DAMPER
STACK
BLACK SMOKE GENERATING EQUIPMENT
BENZENE STORAGE
d
TRANSMISSOMETER
FUEL OIL
STORAGE
GASOLINE ENGINE
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b
EXHAUST MANIFOLD I>0> FAN
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DAMPER
WHITE SMOKE GENERATING EQUIPMENT
LIGHT SOURCE
SMOKE STOPS
FAN
b
STACK
SMOKE STOPS
PHOTOCELL
U
b
FAN'
TRANSMISSOMETER
B-133
-------
Ringelmann Chart and Equivalent Opacity
b. White Smoke System (Figure 4)
White smoke is created by vaporiz-
ing number two fuel oil in the ex-
haust manifold of a gasoline engine.
Smoke density is varied again by
adjusting the fuel rate. This sys-
tem is capable of producing from
zero to one hundred percent
equivalent opacity'"'.
c. Transmissomcter System
(Figure 4)
The transmissometcr is a simple
light source and photocell combina-
tion, used to measure the light
transmission permitted by the
particular smoke being produced.
The percent transmission is read
off a inicroammeter calibrated
from zero to number five Ringel-
mann and zero to one hundred per-
cent equivalent opacity. The light
to photo-cell path is approximately
four feet in length, but only one
foot of length is exposed to the
smoke. The remaining three feet
are continually flushed with ambi-
ent air to prevent smoke buildup.
The apparatus is calibrated using
several grades of neutral filters.
2. Conduct of School
Training on the smoke generator begins
with the familiarization of the personnel
with known densities of black and white
smoke. Upon the sound of the horn, the
instructor calls out the reading from the
meter. After the familiarization period of
about 1 hour duration, the personnel are
ready for testing for record. Readings are
taken at the sound of the horn and after
each set of 25 readings, the transmissom-
etcr readings arc entered and the devia-
tions calculated (Figure 3). Approximately
16 sets of readings are taken for record
in the course of a smoke school.
An inspector can qualify as an expert
smoke reader by the County of Los Angeles
Air Pollution Control District Standards
when his average deviation (Figure 3) is
not more than 10 percent and no reading
varies by 1 Ringelmann or 20% opacity or
more for a set of 50 consecutive readings.
Consistency must be shown in all his read-
ings under all conditions of light. Addi-
tional training is necessary if an inspector
does not meet all of the above standards.
B-134
IV. FIELD EVALUATION OF PLUMES
A. After his training in a smoke school and
qualifying on the smoke generator, the in-
spector is ready to apply what he has learned
in the field. Although there are general rules
or guidelines which should be followed as
closely as possible, they cannot be held as
hard and fast rules and often the inspector is
called upon to use his good judgment. In
general the rules are as follows:
1. Gray and black smoke is read in densities
and recorded in Ringelmann numbers.
2. Any other colored emissions are read in
opacities and recorded in percentages.
3. If possible, the sun should be at the
observer's back during daylight hours.
4. The light source should be behind the
plume during hours of darkness.
5. If possible, readings should be taken at
right angles to the wind direction and
from any distance necessary to obtain a
clear view of the stack and background.
6. Readings should be made through the
densest part of the plume and'where the
plume is no wider than the diameter of
the stack.
7. An inspector should not study the plume
as this will soon produce fatigue and
cause erroneous readings. Instead, he
should glance at the plume and record his
observation immediately, looking away
from the plume between readings.
Recording Visible Emissions
The rules listed below are generally those used
by the County of Los Angeles Air Pollution Con-
trol District. These are just meant to be a guide-
line and may vary entirely with the wording of the
law.
1. All information should be recorded in the
appropriate space on the form (Figure 2).
2. Readings should be taken at 15 second
intervals and entered on the form.
3. -Any changes in the color of the plume
should be noted under remarks on the
form.
4. A Notice of Violation should not be.issued
unless the source exceeded the Ringel-
mann number or opacity rule for at least
one minute in any one hour beyond the
time allowed by the rule.
-------
Ringlemann Chart and Equivalent Opacity
5. Any hour means any consecutive sixty
minute period.
6. Photographs should be taken before or
after but not during visual
determinations.
7. The same general rules apply to reading
emissions from moving sources.
Flumes Containing Steam
Accuracy in reading is naturally affected when
plumes contain a large amount of steam. Steam
is not often considered to be an air contaminant,
yet it docs retard the transmission of light
through the plume. It is noted, however, that
the steam dissipates a short distance from the
source. Opacity readings may be taken im-
mediately beyond this point, if steam is to be
discounted, although this gives the source a
decided advantage. If the source still appears
to be in violation, it may be necessary to wait
for a hot, dry day, when the steam dissipates
upon entering the atmosphere, to record a series
of readings.
Night Readings
To read at night it is necessary to choose a
viewing site where a source of light is behind
the plume and evaluate the transmission of this
light through the plume. If night readings are
anticipated, they should be included as part of
the training.
6. Kowalczyk, John F. , Purpose and Operation
of a Smoke School - National Center for Air
Pollution Control, Cincinnati, Ohio, Control
Development Program, Engineering Control
Section - Presented at the APCA National
Conference, Cleveland, Ohio, June 1967.
7. Sholtes, R. S. , Ph. D. , Operation of the
Mark II, Smoke Observers Training Unit,
1967.
8. Department of Health, Education and Welfare,
Air Pollution Control Field Operation Manual,
Washington, D. C. 1962.
9. Yocum, John E., Air Pollution Regulations -
Their Growing Impact on Engineering
Decisions. Chemical Engineering, Vol. 69;
103-114, July 23, 1962.
REFERENCES
1. Kudlich, Rudolf, R in gclmann Smoke Chart,
United States Department of the Interior,
Bureau of Mines Information Circular
No. 8333, Revised by Staff, May 1967.
2. L. E. Burncy, Title 42 - Public Health,
Chapter 1 - Public Health Service, Depart-
ment of Health, Education, and Welfare.
Subchapter F - Quarantine, Inspection,
Licensing. Part 75 - Smoke Inspection
Guides, February 26, I960.
3. Los Angeles, County of, Air Pollution Con-
trol District, APCD Rules and Regulations,
Chapter 2, Schedule 6, Regulation 4,
Prohibitions - Rule 50 - p. 17.
4. People vs Plywood Manufacturers of Cali-
fornia, 291 P. Ed. 587/1955/California.
5. People vs International Steel Corporation
226 P. Ed. 587/1951/California.
B-135 and B-136
-------
EQUIVALENT OPACITY
A Useful and Effective Concept for
Regulating Visible Air Pollutant Emissions*
I INTRODUCTION
A majority of the smoke-control programs
that evolved in this country limit visible
emissions to the atmosphere, using the
Ringelmann Chart. This chart was developed
about 1890 and has been widely applied in
controlling emissions of visible black smoke.
The Ringelmann Chart is a method of judging
the optical density or opacity of a gray or
black smoke plume by reference to a chart.
Now that many of the smoke-control programs
in urban areas are evolving in air pollution
control programs, all types of processes
have come under scrutiny and a method of
regulating visible emissions regardless of
color is not only desirable, but necessary.
Many jurisdictions have extended the use of
the Ringelmann Chart by limiting such
visible emissions not only to a shade of gray
but also to "such opacities as to obscure an
observer's view to a degree equal to or
greater than does smoke" of Ringelmann No.
2 shade. Thus, the term "equivalent opacity"
refers to the extension of the Ringelmann
Chart to judge the degree to which a visible
plume of any color obscures the view of the
observer. Experience has shown the equiva-
lent opacity concept to be an important tool
in the conduct of a vigorous air pollution
control program.
II THE NEED FOR CONTROLLING VISIBLE
EMISSIONS
The fundamental reasons for restricting
visible emissions at the source are:
1) Reduce the soiling power of a
community's air, i. e., a cleaner
community.
*Prepared for presentation to East-West Gateway
Coordinating Council Hearings on the Proposed
Interstate Air Pollution Study Recommendations
St. Louis, Missouri, September 27, 1966.
2) Improve visibility, i. e., the capability
of seeing through the atmosphere, and
3) Prevent the introduction of aerosols in-
to the atmosphere which could directly
or indirectly contribute to adverse
human health effects.
Visible man-made air pollution consists of
smoke, dust, mists, and fumes. Among the
numerous sources of visible pollution are the
burning of fossil fuels to provide heat and
power, the disposal of refuse and wastes
from human activity, industrial milling and
grinding, iron and steel processes, petroleum
refineries, the operation of motor vehicles
such as diesel buses and private automobiles.
One class of particulate emissions are large
particles of dust or soot generally greater
than 10 microns in size. (25, 000 microns =
one inch) These particles fall to earth rela-
tively fast and are responsible for a good
deal of the nuisance and soiling effects of air
pollution. Particles greater than 10 microns
in diameter are large compared to the wave
length in the visible spectrum; thus, the ob-
scuration of light is due mostly to absorption
rather than diffuse scattering. Particles of
this size are usually intercepted in the upper
respiratory system.
Another form of visible emission is the
aerosol whose size range is about 2 microns
and below. This size particle represents a
liquid or solid in a highly dispersed state
and remains suspended in the atmosphere for
long periods of time. The chances for phy-
sical or chemical interaction in the atmosphere
for these small particles are many times
greater than that for large particles due to
the greater surface area, mobility and time
of. suspension. These facts make the emission
B-137
-------
Equivalent Opacity
of small particles a very important factor,
not only in air pollution problems, but in
general climatological outlook. One well-
known manifestation of such interaction by
aerosols is their capacity for the accumula-
tion of water molecules at high relative
humidity, thereby causing fog and cloud form-
ations. Johnstone, et al, have demonstrated
the catalytic potential of certain aerosols to
oxidize SO2 to 803, thereby forming sulfuric
acid. Other research work indicates syner-
gistic intensification of certain irritants in
the presence of certain neutral aerocolloidal
matter. These small particles can enter the
lower respiratory tract and the retention may
be on the order of 25 percent. Retention is
more likely whenever condensation in the
saturated atmosphere in the lung increases
the particle size.
Studies have shown that particles in the size
range of the visible spectrum (. 2 to . 8
microns) wave lengths of light are the most
effective in scattering light. The scattered
light is the haze which hangs over many cities.
Studies have also shown that polluted atmos-
pheres reduce solar radiation by 25 to 75
percent of that received outside of the polluted
areas.
Ill HISTORICAL DEVELOPMENT OF
EQUIVALENT OPACITY
The most wide-spread control of visible
emissions is based on the Ringelmann Chart
and has been aimed at the control of black
smoke. In a great many communities some
limitation on the emission of black smoke is
the only specifically stated emission limita-
tion. As previously mentioned, the Ringel-
mann Chart was developed in about 1890 by
Maximillian Ringelmann, a professor of Agri-
cultural engineering in Paris. It was
apparently introduced into this country in about
1897 and first incorporated into law in Boston
in 1910. The Ringelmann Chart, as published
by the U.S. Bureau of Mines, consists of
four cross-hatched sections, each measuring
5-3/4" X 8-1/2". The width of the black
lines in the cross-hatching of each chart
corresponds to a certain percentage of black.
thus Ringelmann No. 1 is equivalent to 20
percent black, Ringelmann No. 2-40 percent,
etc. These charts are then displayed between
the observer and the smoke source. The lines
on the chart appear to merge into various
shades of gray and the smoke emission
is then matched with one of the cross-hatched
areas on the chart. The validity of using the
Ringelmann Chart as a standard and the read-
ing of smoke emissions without physical
reference to the Ringelmann Chart have been
well established in the courts.
Many jurisdictions have extended the use of
the Ringelmann Chart by the inclusion of the
equivalent opacity concept. The first appear-
ance of this concept may have been in air
pollution control ordinances of the County of
Los Angeles in 1945. In 1947 the Health and
Safety Code of the State of California was
amended to provide for the establishment of
county-wide air pollution control districts.
One section of this act limits visible emissions
for a given period of time, not only to
Ringelmann No. 2 shade of gray but also any
visible emission of such opacity as to obscure
and observer's view to a degree equal to or
greater than Ringelmann No. 2. Thus it is
mandatory for any air pollution control dis-
trict in California formed under this law to
use the equivalent opacity concept. The Bay
Area Air Pollution Control District (San
Francisco), formed by a different enabling
act, uses this same equivalent opacity
concept.
Until relatively recent times, the equivalent
opacity concept was not extensively used out-
side of California. The following list of
jurisdictions are known to have incorporated
the equivalent opacity concept into their air
pollution control regulations.
Municipalities
Chicago, Illinois
Cleveland, Ohio
Philadelphia, Pennsylvania
New York, New York
Washington, D. C.
East Chicago, Indiana
B-138
-------
Equivalent Opacity
Regions and Counties
Los Angeles County, California
San Francisco Bay Area, California
Riverside County, California
San Bernandino County, California
Orange County, California
Sacramento County, California
San Diego County, California
Monterey County, California
San Joaquin County, California
Cook County, Illinois
Dade County, (Miami) Florida
Sarasota, Florida
Jefferson County (Louisville,) Kentucky
Guilford County, North Carplina
Five Suburban Cities (Cincinnati, Ohio
area)
State
Colorado
In addition to the above list there are numer-
ous communities which are now proposing
control regulations which include an equiva-
lent opacity provision. This list evidences
the growing nation-wide concern about the
control of air pollution along with the reali-
zation that equivalent opacity is a necessary
and practical tool for the adequate enforce-
ment of an air pollution control program.
IV EVALUATION OF EQUIVALENT OPACITY
AS A REASONABLE AND EFFECTIVE
TOOL IN CONTROLLING AIR POLLUTION
From the standpoint of the responsible air
pollution control agency, some of the advant-
ages of the use of visible emission control
regulations, including the equivalent opacity
concept are:
1) The validity of using the Ringelmann
Chart is well established in the field
of air pollution control legislation. The
validity of the equivalent opacity con-
cept has also been established by the
courts. The statement of the court
regarding the equivalent opacity was:
"Subsection (a) (referring to the black
smoke section) only begins to solve the
problem of the discharge of contaminants
into the air; it does not touch smoke and
other substances too light in shade to
come up to Ringelmann No. 2. They
may be so substantial in material, how-
ever, that they make it impossible to
see an object on the other side. We
have all seen very white smoke that
shuts out the view completely. Again
they may obscure the view to a lesser
degree than totality" . . . "We may,
therefore, express the test of Subsec-
tion (b) (equivalent opacity section) in
simple terms: it condemns smoke or
any other contaminant that is at least
as hard to see through as is smoke
which is as dark or darker than Ringel-
mann No. 2. There is nothing mystic
or incomprehensible about such a state-
ment. "
2) Observers can be trained in a relatively
short time and it is not necessary that
observers have an extensive technical
background (see Air Pollution Control
Field Operations Manual, Chapter 10,
regarding training of air pollution in-
spectors in Los Angeles).
3) No expensive equipment is required.
4) One man can make many observations
per day.
5) Violators can be cited without resorting
to time consuming source testing.
6) Questionable emissions can be located
and the actual emissions then deter-
mined by source tests.
7) Although it is usually not possible to
quantify the reduction in total air
pollution by the control of visible'
emissions, it is reasonable to assume
that there will be a reduction in the
discharge to atmosphere of dusts,
gases, and mists.
B-139
-------
Equivalent Opacity
8) Control can be achieved for those
operations not readily suitable to regu-
lar source testing methods. Examples
are dust and other leakage from process
equipment, visible automobile exhaust,
and bulk loading or unloading of dusty
materials as grains, coal, ores, etc.
9) It would be unfair to many processes
and operations if dust concentrations
in the effluent gases were limited such
that visible emissions would be
eliminated.
The most common objections to the use of
equivalent opacity are:
1) The opacity observed is a subjective
measurement varying with the position
of the observer in relation to the sun .
and sky, size of particles in the plume,
atmospheric lighting and background
of-the plume.
This same objection has been used for
many years against the use of the
Ringelmann chart for gray smoke, but
to date no other method has been found
to be as practical and useful. It has
been shown that with adequate training,
an observer can reduce, although not
eliminate, the effects of many of these
variables. Multiple observations,
under varying atmospheric conditions,
tend to reduce some of the effects of
the background and atmospheric light-
ing. An experienced observer can
learn to weight the opacity readings
according to various conditions.
2) Opacity has not as yet been successfully
correlated in detail with other methods
of measurement.
A knowledge of the processes emitting
a visible plume permits an observer to
make a rough judgment of the normalcy
of that process or operation. Thus,
the appearance of the reddish-brown
nitrogen dioxide gas at the stack of an
ammonia oxidation unit indicates the
efficiency of the recovery system. A
rough estimate can be made of the sul-
fur content of fuel oil used in process
furnaces or boilers by the appearance
of the stack. A high sulfur fuel will
give a bluish appearance to the dis-
charge. Therefore, it is important
that the observer have a knowledge of
the process producing the visible
emission.
3) Gaseous emissions cannot be determined
by equivalent opacity.
The use of equivalent opacity does not
by itself constitute a complete and
vigorous air pollution problem. It does
not eliminate the need for qualified
technical personnel, source tests,
knowledge of air pollution emission, and
sound engineering and administrative
judgment. In fact, there is no known
law or concept that in itself can com-
pletely eliminate all forms of air pollu-
tion. It is reasonable to assume that
the elimination of visible emissions
will reduce dust and aerosol emissions
and at the same time eliminate some
gaseous pollutants.
4) Difficult to use accurately in the hours
of darkness.
Experience in Los Angeles has shown
that the use of a light source behind a
plume permits readings to be taken at
night.
5) Water droplets interfere with the equi-
valent opacity observations.
Since water is not normally considered
an air pollutant, some allowance must
be made for those visible plumes whose
opacity is derived from uncombined
water droplets. The Bay Area Air
Pollution Control District exempts
visible emissions which violate the
opacity rule because of uncombined
water. To those who administer an
equivalent opacity rule, the "wet plume"
presents a problem in a few cases, but
the problem is not an insurmountable
B-140
-------
Equivalent Opacity
one. In the absence of an objective
method for reading wet plumes, it is
necessary to make multiple observa-
tions under varying conditions of atmos-
pheric relative humidity. It is then
possible to make judgments based on the
observations and a knowledge of the
process and emissions involved. One
method used to read wet plumes is to
determine the opacity at that point in
the plume where the water vapor dis-
sipates. This admittedly is not always
an ideal solution to the problem. An
objective test using a photometer has
been proposed for determining the
opacity of wet plumes. It appears that
this approach holds some promise for
handling many cases of this type.
REFERENCES
S. Smith Griswold. Air Pollution Control
Field Operations Manual. Public Health
Service Publication No. 937. 1962.
H. F. Johnston and A. J. Molls. Forma-
tion of Sulfuric Acid in Fogs. Industrial
and Engineering Chemistry. October
1960.
V SUMMARY
The need for restricting visible air pollutant
emissions and the development of the Ringel-
mann Chart and the equivalent opacity concept
is briefly explored. The use of the equivalent
opacity type regulation started in California
and has recently spread to several other mun-
icipal and county jurisdictions. One state,
Colorado, has an equivalent opacity provision
in its air pollution control regulations. Some
of the advantages in using an "equivalent
opacity" regulation are delineated and some
objections are listed and rebutted. Although
there are valid objections to equivalent opacity,
the advantages far outweigh the objections.
Until the development of more objective
methods of plume evaluation, the equivalent
opacity regulation is recommended as a
necessary and useful tool in the operation of
a vigorous air pollution abatement program.
B-141 and B-142
-------
INDEX
D
m
X
-------
INDEX
agricultural burning, A-20
aluminum industry, A-28, A-29, B-84
analysis
proximate, A-11, B-17
screen, A-ll, B-19
ultimate, A-ll, B-17
anemometer, A-53
anticyclone, A-49, B-107
anthracite coal, A-ll, B-19
appeals of visible emissions regulations, A-55
arch, A-12
area source, A-37, B-l
ash, A-ll, A-16, B-3, B-16, B-47, B-56
ash content of fuel, A-6, A-19, B-17, B-36, B-43,
B-47, B-86
asphalt, air blowing of, A-29, A-30, B-81
asphalt batch plants, A-32, B-82
basic oxygen furnace, A-25, A-28, B-81
Beaufort Scale of wind speeds, A-53
bituminous coal, A-ll, B-19
blastfurnace, A-27, B-79, B-81
boilers, A-13, B-33, B-44
fire-box, A-13, B-33
fire-tube, A-8, A-13
sectional, A-8
water-tube, A-8, A-13, B-33
breeching, A-12, B-36, B-46, B-59, B-67
Bunker C oil, A-6
burner, oil, A-6, B-21, B-22, B-23, B-24, B-25
air atomizing, A-7, B-21
mechanical atomizing, A-7, B-22, B-23
rotary cup, A-7, B-24, B-25
steam atomizing, A-7, B-21, B-22
vaporizing, A-7, B-21
carbon in fuel, A-ll, A-14
carbon in,smoke, A-14
catalyst regenerator, A-29, A-30, B-81
cement plants, A-30, B-82
cenospheres, A-9
chlorine, A-l
circumvention, A-44
cloud, A-38
cloud cover, A-53
clouds, A-50
coal, A-ll, B-17
analysis, A-ll
anthracite, A-ll, B-19
bituminous, A-ll, B-19
lignite, A-ll, B-17, B-19
coal burning units
cyclone, A-15
pulverized-fuel, A-15
stokers, A-15
coke, A-14, B-18, B-83
coke plant, A-28, B-83, B-84
color or shade of plume, A-22, A-32, A-33, A-34,
A-38, A-60, B-71, B-95
combustion, 3 T's of, A-3, B-9, B-39, B-57
common law, A-55, B-119, B-120, B-121
coning, B-115, B-116
copper industry, A-28, A-29, B-84
cracking, A-6, B-15, B-16, B-21, B-81
crude oil, A-6
cupola furnace, A-25, B-81
cyclone (low pressure area), A-49, B-107
cyclone collector, A-10, A-17, A-33, B-48, B-81,
B-82, B-85
cyclone furnace, A-15, B-30, B-32, B-36, B-43
decomposition (cracking), A-8
density, smoke, A-40
detached plume, A-10, A-52
detergent manufacture, A-34, B-84, B-85, B-91
diesel engine, A-21, A-23, B-l37
distillate oil, A-6, A-9, B-15, B-16
downwash, A-51, A-53
draft, A-13, B-45, B-67, B-69
forced, A-8, A-13, B-33, B-46, B-60, B-67
furnace, A-13
induced, A-8, A-13, B-33, B-46, B-60, B-67
natural, A-8, A-13, B-40, B-45, B-60
driers, A-26
compartment or tray, A-26, B-91
flash, A-26
rotary, A-26, A-32, B-82, B-91
spray, A-26, A-34, A-35, B-85, B-86, B-91, B-92
dry adiabatic lapse rate, A-48
dust, A-l, A-32, B-3, B-4, B-5, B-6, B-7, B-83, B-137
economizer, A-13, A-31, B-33, B-44, B-53, B-54
eddies, A-50, A-51
effective stack height, A-48
effects of particulates, A-l
health, A-l
materials, A-l
sunlight, A-l
vegetation, A-2
visibility, A-l
electric furnaces, A-25, A-28, B-81, B-83
electrolytic reduction, A-26, A-29
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Index
electrostatic precipitator, A-10, A-17, A-30, B-48, B-81,
B-82, B-83, B-84, B-85
emission factor, A-37
emission generator, A-60, A-61
engines
diesel, A-21, A-23, B-137
gas-turbine, A-21, A-22, A-23
internal combustion, A-21
equivalent opacity, A-40, A-55, B-97, B-129, B-134,
B-137, B-138, B-139, B-140, B-141
excess air, A-3, B-10, B-50, B-54, B-55, B-60
expert witness, A-56, A-57, A-58
fabric fQters, A-30, A-34, B-48, B-81, B-82, B-83, B-86
fanning, A-48, B-115, B-116
film strip, A-42
fixed carbon, A-11, B-18
Hares, A-29, B-71, B-72, B-73
flyash, A-l, A-18, B-47, B-50, B-60, B-69, B-95
flyash reinjection, A-15, A-16, A-19, B-51
fog, A-50
foundry, gray iron, A-25, B-3, B-5, B-81
fronts, A-49, A-52, B-107, B-108
cold, A-49, B-108, B-113
occluded, A-49
stationary, A-49, A-52
warm, A-49, B-108, B-113
fuel bed, A -12
fumes, A-l, B-3, B-4, B-5, B-7, B-84, B-137
fumigation, B-115, B-116
furnaces
basic oxygen, A-25, A-28, B-81
blast, A-27, B-79, B-81
crucible, A-25
cupola, A-25, B-81
electric, A-25, A-28
open-hearth, A-25, A-28, B-81
pot, A-25
reverberatory, A-25, A-28, B-85
gas, A-l, A-22, B-4
gas turbine engine, A-21, A-22, A-23
gasoline engine, A-21
generator, smoke, A-60, A-61
greenhouse effect, A-48, B-103
haze, A-l, A-50, A-52
heat exchange equipment, A-12, A-13, B-32
heat exchanger, A-13, A-21, B-32
high pressure area, A-49, A-52, B-107
humidity, A-34, A-35, A-50, A-52, B-90
hydroxylation, A-8, B-14, B-21
ignition temperature, B-9
incinerators, A-18, A-19, A-59, B-63, B-65, B-66,
B-67, B-69, B-70
apartment house, A-18
conical (tepee), A-18, A-19
multiple chamber, A-18, B-61, B-63, B-65
municipal, A-18, B-63
rules for minimizing emissions, A-19
single chamber, A-18, B-63
internal combustion engine, A-21
inversions, A-48, A-49, A-52, B-104, B-106,
B-113, B-115
iron and steel manufacture, A-25, A-27, A-28,
B-3, B-79
isobars, A-49, A-52
jet engine, A-21, A-22, A-23
kiln, rotary, A-30, B-82, B-84
kraft pulp mills, A-30, B-82
lapse rate of temperature, A-48, A-51, B-105,
B-106, B-107, B-115, B-116
laws
nuisance, A-40, A-55, B-119, B-120, B-121
visible emissions, A-22, A-55, B-97, B-127,
B-129, B-138
lead industry, A-28, A-29, B-84
lead oxide, B-7
lidar, A-42
lignite coal, A-11, B-17, B-19
lime industry, A-30
looping, A-48, B-115, B-116
low pressure area, A-49, A-50, A-52, B-107, B-108
metallurgical processing, A-26
micron, A-l
mist, A-l, B-3, B-4, B-6, B-7, B-137
mobile sources
reading of visible emissions from, A-22, A-43
moisture content, A-11, A-19, B-17, B-43
natural gas, A-20, B-39
burners, A-21
combustion, A-20, B-15
composition of, A -20
nitric acid, A-32
nitrogen dioxide, A-l
nocturnal inversion, A-49, A-52
nuisance, A-40, A-55, B-119
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Index
oil, B-15
ash content, A-6
Bunker C, A-6
burners, A-6, B-21
crude, A-6 ,
distillate, A-6, B-15
grades, A-6
residual, A-6, A-7, B-15
sulfur content, A-6
viscosity, A-6
oil refining, A-29, A-30, B-4
opacity, A-40, A-55
open burning, A-20, A-30, B-81
open hearth furnace, A-25, A-28, B-82
overfeed beds, A-13
overfeed stoker, A-12, A-15, B-31, B-40
overfire air, A-4, A-12, A-13, A-14, B-28
oxidation zone, A-12
paint manufacture, A-32
particle size, A-14, A-19, A-22, A-23, A-28, A-29,
A-30, A-32. A-33, A-40, A-43, A-50. B-79, B-81,
B-82, B-84, B-97, B-137, B-138
particulates, A-9, A-50
petroleum refining, A-29, A-30, B-81
phosphate fertilizer manufacture, A-33
phosphoric acid manufacture, A-33, B-83
photoelectric cell, A-42, A-60, B-127, B-134
plume, A-38
detached, A-10, A-38, A-52
plume rise, A-48
point source, A-31, B-l
Portland cement, A-30, B-82
preheater, A-13, B-44, B-54
primary air, A-12, B-39, B-43, B-45, B-46, B-57, B-60
proximate analysis, A-ll, B-17
pulverized-fuel firing unit, A-15, B-29, B-30, B-32,
B-34, B-42, B-43
quenching, A-27
radiant heat absorbers, A-13
radiation, A-48, B-103
radiation inversion A-49, A-52, B-115, B-116
reduction zone, A-13
refining, metallurgical, A-26
refining, oil, A-29, A-30, B-15
refractory material, A-12, A-27, A-30, B-44, B-45
regenerator, catalyst, A-29, B-81
regulations, A-2
air quality, A-2
grain loading, A-2, A-40
opacity, A-2
regulations (Continued)
process weight, A-2
shade density, A-2
thermal input, A-2
visible emissions, A-22, A-43
weight concentration, A-2, A-40
relative humidity, A-34, A-35, A-50, A-52, B-90,
B-138
residual oil, A-6, A-7, A-9, B-15, B-16
Ringelmann Chart, A-40, A-41, A-55, B-95, B-96,
B-97, B-98, B-123, B-124, B-125, B-126, B-129,
B-134, B-137, B-138, B-139, B-140
roasting, A-26
rotary kiln, A-30, B-82, B-84
rules for smoke readers, A-45
scattering of light, A-50, A-52, B-137
secondary air, A-13, B-34, B-39, B-57, B-60
settling chamber, A-16, B-48
sintering, A-26, A-27, B-79
slagging, A-14
smelting, A-26, B-3, B-84
smoke, A-l, A-3, A-14, A-18, A-40, B-3, B-4,
B-5, B-6, B-7, B-9, B-21, B-55, B-71, B-137
smoke comparison chart, A-41, A-42
smoke generator, A-60, A-61, B-135
Smoke Inspection Guide, A-42, B-127
Smokescope, A-41, B-96, B-124, B-125, B-127
Smoke Tintometer, A-41, B-96, B-127
soap manufacture, A-34, B-84, B-85
soot, A-l, A-3, A-14, B-9, B-14, B-21, B-55, B-56,
B-71, B-95
soot blowing, A-8, A-10
source test, A-40, A-44
spreader stoker, A-15, B-27, B-28, B-31, B-34, B-41,
B-42, B-51
stability, atmospheric, A-48, A-52, A-53, B-105, B-112
statute law, A-55, B-120
stokers, A-12
overfeed, A-12, A-15, B-31, B-40
spreader, A-15, B-28, B-31, B-34, B-41, B-42, B-51
traveling grate, A-15, B-27, B-28, B-31, B-34
underfeed, A-12, A-15, B-27, B-31, B-40, B-41
vibrating grate, A-15, B-28, B-32
subsidence inversion, A-46, B-l06, B-115
sulfuric acid manufacture, A-31, B-83, B-84
sulfur content, A-6, A-ll, A-12, B-17
sulfur in coal, A-12, B-18, B-44, B-48, B-49, B-50
organic, A-12, B-18, B-48, B-49
pyritic, A-12, B-18, B-19, B-48, B-49
sulfur trioxide, A-9, A-31, B-49, B-50, B-71, B-83,
B-85, B-90, B-91. B-97
superheater, A-13, B-33, B-44, B-53
sweating, A-26
-------
Index
tar, A-14
temperature inversions, A-48, A-49, A-52, B-104,
B-106, B-113, B-115
tepee burner, A-18, A-19
three T's of combustion, A-3, A-16, B-9, B-39, B-57
transmissometer, A-60, B-131, B-134
traveling grate stokes, A-15, B-27, B-28, B-31, B-34
turbulence, A-3, A-7, A-50, A-51, B-ll, B-lll, B-112
ultimate analysis, A-11, B-17
Umbrascope, A-41, B-96, B-127
underfeed, A-12, A-13, A-15, B-27, B-31, B-40, B-41
underfire, A-12
vapor, A-l, B-3, B-4, B-55, B-6
varnish manufacture, A-32
vibrating grate stoker, A-15, B-28, B-32, B-34
viscosity, A-6, B-16
volatile matter in fuel, A-11, A-16, B-18, B-36
volatile products, A-14
water vapor plumes, A-34, A-35, A-44, A-52, B-89,
B-90, B-91, B-92, B-97, B-138
wet scrubber, A-17, A-33, A-34, A-35, B-48, B-81,
B-82, B-85, B-91
wind, B-107, B-lll
direction, A-46, A-53, B-lll, B-112, B-134
speed, A-46, A-52, A-53, B-lll, B-112, B-113
witness, expert, A-56, A-57, A-58
zinc industry, A-28, A-29, B-84
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