-------
Fundamentals in Combustion Calculations
H
(specific fuel) =
H.V.
(Fig. 3)
HA
H (specific fuel) = — —
« ti. V .
(Fig. 3)XH.V_ (specific fuel)
H (Pitt, natural gas) =
HA /NaturalX /Pitt.X
— - gas in }X H.V._ (natural)
'V-G \Fig. V C Vgas/
/Pitt.X
HA (naturalj =
\gas/
x
29J
/
X1129 BTU per cubic foot
The available heat (HA) for Pittsburgh
natural gas is 915 BTU per cubic foot.
The available heat for the boiler at 500°F
and theoretical combustion equals
9, 150,000 BTU per hour.
If 20 percent excess combustion air was
used, the available heat at 500°F would
be decreased to about 79 percent of the
gross heating value for natural gas
(calculated from Figure 4).
REFERENCES
1 Anon. North American Combustion Hand-
book, 1st Ed., Copywrite 1952 by
. North American Manufacturing Company,
Cleveland, Ohio.
2 Hougen, O.A. Chemical Process Prin-
ciples Part I, 2nd Ed. , Copywrite 1954
by John Wiley and Sons, Inc.
-------
Section 2
BURNING OF FOSSIL FUELS
Facts About Fuels
Natural Gas Burning
Gas Burning Equipment
Natural Gas Fired Installations-Design
Considerations
Fuel Oil Burning
Oil Burning Equipment
Fuel Oil Burning-Design Parameters
Fuel Oil Burning-Good Operation Practices
Coal Burning
Coal Burning Equipment
Coal Burning-Design Parameters
Coal Burning-Good Operation Practices
Selected Publications
Underfeed Stokers
Spreader Stokers
Another Look at the Traveling Grate Stoker
Corroision and Deposits from Combustion Gases
-------
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 (C?Hp) 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
-------
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 subt racting 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.
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.
-------
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 coal' 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.
-------
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 like 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
Grindability. 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.
-------
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, passinga4 3/8-in. retained on
3 1/4 in.; egg, 3 1/14 to 2 7/16; stove,
2 7/16 tol 5/8; chestnut, 15/8 to 13/16;
pea. 13/16to9/16; No. 1 buckwheat, 9/16
to 5/16; No. 2 buckwheat (barley), 3/16 to
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.
-------
Facts About Fuels
If heat liberated by oxidation is confined
to a small area, temperature rises,
increasing reaction rate. This cycle of
rising temperature and faster oxidation
continues until "hot spots" form and
spontaneous combustion occurs.
To guard against such troubles: (1)
Remember that small sizes pack tighter
and present more surface, making them
likelier to heat. (2) Avoid piling coal
in hot weather or in a heated space.
( 3) Don't crush before piling, and watch
pile closely during first three months
since fresh surfaces oxidize more
readily. (4) Avoid segregation of sizes
by building the pile up in layers, leveling
off and compacting each. (5) Check pile
regularly, especially 5 to 8 ft below the
surface of the flanks - temperature
over 140-150 F means danger point is
reached at which coal must be withdrawn.
For storage details, see POWER, Sept.
1942, p 643.
Sampling. Coal composition varies with-
in a given seam or mine and even
between points several feet apart on the
face. Although shipped from one point,
coal composition varies from car to car
and from one part of a car to another.
Understanding the nature of all these
variations makes it possible to use
laboratory tests intelligently.
To begin with, a laboratory analysis,
according to approved standards, re-
presents within an extremely small
margin of error characteristics of the
sample on which it is made. How well
the analysis represents the lot of coal
involved depends on sampling methods.
Until recently, size of gross sample
was thought to be of major importance
for accurate sampling.
Recent research shows accuracy of
sample depends on number and size of
increments composing it rather than on
its weight. Proof of this point makes
possible use of much smaller samples
and simplifies reduction of gross sample
to laboratory dimensions.
E Sampling Procedure
New ASTM standard distinguishes between
"commercial" and "special-purpose"
sampling and bases sample size and
number of increments on coal size and
expected ash content. Note that increment
refers to quantity of coal obtained by a
single sweep of the sampling instrument;
where possible coal should be sampled
while in motion.
The standard provides for mechanical
sample preparation and subdivision by
large and small riffle samplers like those
used in the laboratory. Commercial
procedure is designed so 95% of test
results fall within plus or minus 10% of
ash content of coal sampled. Correct
determination of ash value indicates
accuracy of other results.
Knowing how closely a given analysis
represents a given sample and lot of coal,
we need also to know how reliable one
test may be in predicting the average
for a series of shipments, or, if average
quality is known, what variation might
be expected in individual shipments.
Recent research shows that for bituminous
coals of less than 9% ash, one-half of
ash determinations depart from the
average by no more than 0. 5%; for coals
of more than 10% ash, deviation is about
twice as much.
Common sense indicates that one test
from one sample from one shipment is a
poor guide. Statistical studies show that
an average of ten shipments is three times
as accurate as a single test while an
average of 20 tests is 4. 5 times as
accurate. Beyond 20 tests, gain in
accuracy is small.
-------
GAS BURNING EQUIPMENT
On the face of it burning gas is simple, be-
cause the fuel is ready for combustion and
requires no preparation in the strict sense
of the word. Nevertheless, the remaining
parts of the job - proportioning, mixing and
burning - can be handled in a variety of ways
and their characteristics need to be known
for sound selection of equipment and success-
ful operation.
I ATMOSPHERIC BURNERS
Gas burners differ mainly in the way air and
fuel mix. Perhaps most familiar is the so-
called atmospheric burner. One form appears
quite generally in the ordinary house-hold gas
range. In it the momentum of the incoming
low-pressure gas stream is used to draw in,
or aspirate, part of the air needed for com-
bustion. A shutter or similar device regulates
amount of air so induced. Gas and air together
pass through a tube leading to the burner ports,
mixing in the process. The mixture burns at
the ports of openings in the burner head (with
a blue, nonluminous flame. Secondary air
is drawn into the flame from the surrounding
atmosphere. Larger counterparts of this
general burner type, having ring or sectional
burner heads with many ports, are used to
fire small boilers and industrial equipment.
A single-port atmospheric burner is shown in
Figure 1. Needle valve controls gas flow
through the spud; air is drawn in around the
shutter at the end. The resulting mixture
passes through the tube and burns at its end.
Single-port burners may be grouped, several
banks high and wide, to serve larger furnaces.
Although physically simple, such a burner
must be proportioned with considerable skill
to conserve the relatively small amount of
energy in the low-pressure gas stream. It
is this energy which entrains the primary
air. How well this is done depends on
primary-air percentage, gas-orifice size,
ratio of mixer throat to burner port area and,
in boilers especially, furnace draft.
II PREMIX PERCENTAGE
With burner-port size and shape fixed, nature
of burning depends largely on amount of pri-
mary air, or premix. With premix low, flame
is long and pale blue. It may have a yellow
tip, indicating some cracking and presence of
free carbon. Increasing primary air shortens
the flame as burning becomes more rapid,
and greenish inner cone appears. When
speed of burning, or flame propagation, ex-
ceeds that of gas issuing from the port, flame
flashes back into mixing tube.
Operation is generally satisfactory with 30 to
70% premix; in some special designs 100%
primary air is used. This premix range gives
a turn down, or capacity range, of about 4 to
1. Usually premix and capacity ranges are
somewhat narrower.
Secondary air is usually drawn in around the
burner and the amount thus depends on the
area of the opening and the draft. Control
may be effected by varying draft or, some-
times, by adjusting opening area by shutters.
The so-called atmospheric burner is one ex-
ample of a general class, in which the energy
of one fluid is used to aspirate the other and
in which part or all primary air mixes with
the fuel in the burner body. The "high-
pressure" burner uses gas at about 20 to 30
psig and air at atmospheric pressure. An-
other type uses compressed air, and the gas
is at atmospheric pressure. The burner of
Figure 6 expands high-pressure gas through
two venturi-sections in series to obtain
thorough mixing in a short distance.
Ill REFRACTORY BURNERS
For boiler firing, a somewhat different type
of burner finds wide use. It depends on natural
or fan draft to draw in all air required for
combustion; hence draft conditions are most
important. Design of Figure 2 employs
*Based on the publication by: Rowley, L. N., McCabe, J. C., and Skrotzki, B.C. A.
Firing. Power, pp 84-85. December 1948.
Fuels and
PA.C.ce.25.9.66
-------
Gas Burning Equipment
Primary or uppt,
,Gos supply
IAimoipharfc got bum»r« pull In th*lr primary
air far combustion by tho action of a stream
of low-prei»uro got expanding through an orlflc*
O Premising of fuol gat and *lr noodod A Vanot placed In th« path of Incom- j Oot lituos from • numbor of tpuds con-
* for combustion takot piac* In a mix- ^ Ing air to thli tunnel burnor act ' noctlng to vortical and horizontal manl-
mg chambor outtldo tho furnaco propor to Impart swirling motion to stroam fold*. Primary air ontori around mo ipodi
I Two-»tago bvrnor »p«r«t*f on hlgh-pro*»uro 901;
" patios Iff through two vontMrl ••ctloni In i«rl«i.
Primary air onffori ihuttor, at Uft, undor Induction
-» Hlgh-proisuro gas htuo* from |ott (n tho >pld«r
' and roactlan vplni tho tpldor to rototo tho fan.
ft*tutting turbulonco glvot prompt, thorough mixing
r So callod low-»r«nur» gat-bvrnor tyitvini work with air undor prefiur*
•* and gai at atmo«ph*rlc condltlant. An Inspirator govornor, loft abovo,
dollvort gat-air ml«twr« at proper proi»wra to burnor blocks, rtghf abovo
-------
Gas Burning Equipment
multiple gas jets, which discharge into the
air stream in such a way that violent agita-
tion results in a short mixing tube or tunnel
of refractory. In the burner of Figure 3,
turbulence vanes impart a swirling motion
to the air entering the tunnel. Each of the
small jets of gas issuing from the multiple-
jet orifice entrains with the air and impinges
it outward against the tunnel walls. This
action gives turbulent, thorough mixing.
In the burner shown completely assembled,
Figure 4, vertical manifolds connect horizon-
tal tubes, which contain individual gas orifices
for the 15 tunnel blocks forming the complete
burner (3 high, 5 wide). Louvers in front of
the burner assembly control air admission.
Each orifice discharges into a refractory
mixing tube or tunnel.
In burners of this type the refractory tunnel
aids in heating the mixture for ignition and
protects metal burner parts from high tem-
perature. The flame can be made relatively
luminous, for high radiant-heat transfer.
Large steam-generating units often employ a
high-pressure (2 to 25 psi) gas burner of the
gas-ring, Figure 8, center-diffusion tube,
or turbulent. Figure 7, design. The gas-ring,
Figure 8, has an annular manifold located
between air register and furnace wall surround-
ing burner opening. Orifices drilled in this
ring spray gas angularly across an incoming
air stream controlled in quantity, velocity
and rotation by the registers.
IV FAN-MIX BURNER
In the burner of Figure 7, gas issues from
jets drilled at an angle in a rotating spider.
Resulting reaction spins the spider and with
it the connected fan. A shutter controls air
drawn in, to maintain desired fuel-air ratio.
Thorough mixing of gas and air result from
the turbulent interaction of jets and air stream;
combustion is completed close to the burner.
Thus far designs in which fuel and air mix in
or at the individual burner have been dis-
cussed. Higher burner head pressure to
overcome variable furnace draft, high over-
load capacity, uniform air-gas mix at all
loads, and single-valve control may be had
in a system in which mixture is made at one
point and supplied to several burners. Such
a system is shown in Figure 5. This is the
low-pressure type; gas is at atmospheric
pressure while air is at 1 to 2 psi.
V INSPIRATOR GOVERNOR
Heart of the system is the inspirator gover-
nor, left, Figure 5. Air passes through the
venturi tube at high velocity to create a low-
pressure region at the end of the straight run
where gas ports are located. This pulls
atmospheric-pressure gas through the ports
into the throat and produces mixing. As
the mixture expands through the inspirator
body its velocity is converted to pressure.
Gas enters the governor under pressure and
flows through the governor valve. A passage
through the governor valve keeps pressure at
governor outlet and on the under side of the
diaphragm the same. With atmospheric
pressure on the other side of the diaphragm,
governor delivers gas at atmospheric
pressure.
The mixture leaving the inspirator governor
contains all air needed for combustion. An
air valve controls the burning rate. The
complete gas-air mixture goes from the
inspirator-governor to a number of individual
burners, usually the tunnel type shown at the
right in Figure 5. This principle of supplying
a complete mixture to a number of burner units
is also found in systems operating with high-
pressure gas and atmospheric air.
Figure 8. Center-Diffusion Tube Gas Burner
Design. Combination gal and oil burnir »>•!
•lth«r fw«l er bath together; iam«
r*gltff«r r«gulaf«* primary air tvpplUd
-------
NATURAL GAS
DESIGN
FIRED INSTALLATIONS-
CONSIDERATIONS
Kurt S. Jaeger*
I INTRODUCTION
The following will consider the major design
parameters for natural gas fired heat
generating installations and the fundamental
requirements for proper operation of the
combustion equipment which is normal to
such installations.
The two major factors which control all other
system design considerations are:
1 The heat exchanger or vessel which is
to be fired;
2 The characteristics and conditions of
the gas to be burned.
A third factor which must be considered with
these two is:
3 The exhaust system for handling the
products of combustion.
While this factor is usually dependent upon
Factor 1, it in turn will have an ultimate
effect on equipment selection and performance.
Let us represent in block form these three
factors from which all other design considera-
tions will arise (Figure 1). This diagram
will provide the basis for looking into each
factor separately and observing how their
individual characteristics correlate and
interlock to provide design information for
the entire installation.
We will enlarge on this basic diagram one
factor at a time, and as we go we will
clarify terms and assign meaningful values
to some of these terms.
Gas
Supply
Heat
Exchanger
Exhaust
System
FIGURE 1
*Chief Burner Engineer, Forney Engineering Company,
Dallas, Texas.
PA. C. ce. 35. 1.67
-------
Natural Gas Fired Installations - - Design Considerations
II Factor 1. THE HEAT EXCHANGER
Gas
Supply
Operational
Requirements
Overall Design
and Efficiency
Combustion
Chamber
Size and Shape
Heat Exchange
Surface Area
Heat
Exchanger
Exhaust
System
FIGURE 2
-------
Natural Gas Fired Installations - - Design Considerations
Here we see the characteristics of the heat
exchanger which constitute its parameters:
A The total surface area of the heat ex-
changer (which is exposed on one side of
its surface to hot gases and on the other
side to the medium to be heated) is a
major design consideration in that this
is what basically determines the heat
input required.
In commercial or industrial boiler
installations, boilers are rated based on
their square feet of heating surface.
Packaged boilers today are commonly
rated on the basis that 5 sq. ft. of heating
surface will produce 1 boiler horsepower,
or 33, 500 btu of useful heat, and some
claim even less surface required per
BHP.
This, then, is our first consideration -
size.
B At the same time we are considering size
and determining heat input requirements,
we must know something of the overall
design of the unit and thereby its overall
efficiency. A heat exchanger with only
one pass of the combustion products
through it may not be nearly as efficient
as one in which the hot gases make
several passes; or, a boiler with large
diameter flue tubes may not be as
efficient as one with smaller tubes; so,
design largely determines heat transfer
efficiency and must be considered. This
information is usually available from the
manufacturer, and, generally speaking,
will be in the neighborhood of 80% overall
efficiency.
Our second consideration then is -
efficiency.
C While we are looking at overall design
we must closely examine the size and
shape of the combustion chamber because,
as we will see shortly, this characteristic
will not only affect burner selection, but
will also establish what our heat release
in the combustion chamber will be, which
in turn determines furnace temperatures.
Normally, heat releases range from
30, 000 to 70, 000 btu per hour per cubic
foot of combustion space, and furnace
temperatures may range from 1300°F to
1900°F.
So, we are thirdly concerned about and
governed by - combustion chamber size
and shape.
D Last but not least, we must know what
medium we are heating, and its end use,
so we can determine the true heat input
requirements, and properly select controls.
Ill Factor 2 - THE GAS FUEL
Figure 3 adds to our second major parameter
the details which must be known in order to
continue with our system analysis.
A The chemical analysis of the gas is the
basis from which we determine how much
air will be necessary for complete
combustion, what we can expect in the
way of combustion products, what the
flame characteristics will be, etc. We
can also determine if the gas contains
any significant amount of troublesome
elements (such as sulfur) which might
require special attention.
Natural gas constituents normally include
methane (CH4), ethane (C2Hg) in widely
varying proportions, and lesser amounts
of nitrogen (N2> and carbon dioxide (CO2>.
-------
Natural Gas Fired Installations - - Design Considerations
Gas Pressure
Available
Operational
Requirements
Specific
Gravity
Overall Design
and Efficiency
Heat Content
Combustion
Chamber
Size and Shape
Chemical
Composition
Heat Exchange
Surface Area
Gas
Supply
Heat
Exchanger
Exhaust
System
FIGURE 3
B
From the gas analysis, the heat content
and the specific gravity of the gas can be
calculated.
Generally speaking we can assign the
following approximate values to these
characteristics of natural gas:
Heat content- 1000 btu/cu. ft.
Specific gravity - 0. 65
Air required for combustion - 10 cu.
ft. /cu. ft. gas (this does not allow for
any excess air).
The pressure at which the gas will be
delivered at the installation is most im-
portant, and the point of delivery must
be defined. All too often it is discovered
too late that the pressure actually avail-
able in the boiler room is much lower
than had been expected, simply because
this point had not be clarified. Burner
sizing is a function of available gas
pressure, so a burner which is selected
to provide a given input at a specified
pressure will be too small at some lower
pressure.
While these designations vary from one
area to another, we normally specify
gas pressure ranges as follows:
"LOW PRESSURE"
"MEDIUM PRESSURE"
"HIGH PRESSURE"
up to 8 osi
(1/2 psig)
8 osi to 3.0 psig
3. 0 psig and up
-------
Natural Gas Fired Installations - - Design Consideration
Before we develop Factor 3, and while
we have Factor's 1 and 2 in mind, let us
see what design considerations can be
derived from the parameters we have
established thus far {Figure 4).
Gas Pressure
Available
Heat Output
Required
Specific
Gravity
Heat Input
Gas Flow
Heat Content
Selection
Burner
Controls
Chemical
Composition
Operational
Requirements
Overall Design
and Efficiency
Combustion
Chamber
Size and Shape
Gas
Supply
Heat Exchange
Surface Area
Heat
Exchanger
Exhaust
System
FIGURE 4
-------
Natural Gas Fired Installations - - Design Considerations
D
IV
Heat output - this really is a basic para-
meter which controls the size of the heat
exchanger itself, but quite often we have
the heat exchanger to start with, and our
problem is to determine its heat output.
This is a function of heat exchange area
and the limits to which we can fire it.
Knowing the heat output required, and the
overall efficiency of the unit, we can
determine heat input required and can
check the feasibility of this required input
against the combustion chamber size. If
heat release per unit of combustion
volume is too high, we must limit the in-
put to a more reasonable value; this in
turn reduces our available heat output.
Having determined heat input, the volume
of gas required to furnish that input can
readily be determined by dividing the total
input requirement (btu per hour) by the
heat content of the gas (btu per cubic foot),
with the quotient being expressed in cubic
feet per hour.
We now have gathered sufficient informa-
tion from which to size and select the
appropriate burner and control equipment;
this selection involves not only considera-
tion of all of the sub-parameters we have
developed, but also some judgement re-
garding the several possible selections
which will present themselves. So that
you may appreciate this, we will review
here various burner classifications in
some detail.
BURNER CLASSIFICATION AND
SELECTION
The two broad and general classifications
into which all burners fall are "atmospheric"
and "mechanical draft", which terms are
descriptive of the means by which the
burner obtains the air which it will mix with
the gas preparatory to the combustion
process.
The atmospheric burner depends entirely
on the negative pressure within the furnace
to draw combustion air through the burner
assembly; or, it could be said that the
difference between atmospheric pressure and
furnace pressure results in air flow through
the burner, hence the term "atmospheric".
In contrast, the mechanical draft burner
includes as one of its components a blower
which supplies all the combustion air to the
burner, and therefore is not dependent on
furnace pressure. The term "forced draft"
is often applied to such burners, though it
is usually restricted to burners which are
designed to work against positive furnace
pressures.
It would be well to note here that there are
some burner designs which may be used
either as atmospheric burners or forced
draft burners. For instance. Figure 4a
shows a burner which has been enclosed in
a plenum, or windbox containing combustion
air under a pressure higher than the furnace
pressure. This same burner could have
been used without the windbox if the negative
pressure in the furnace had been sufficient
to overcome the draft loss of the burner
register. The point here is that the manner
in which the burner is finally applied deter-
mines how it is classified in that particular
instance.
Within these two broad classifications of
atmospheric and mechanical draft, gas
burners can be further subdivided into type
and styles which can be defined as follows:
-------
Natural Gas Fired Installations - - Design Considerations
AIR REGISTER
GUIDE PLATE
BURNER GUIDE TUBE
OUR
GAS GUN -EJ
HIGH ALLOY DEFLECTOR
GUN NOZZLE
REFRACTORY BURNER TILE
BOILER CASING PLATE
SPIDER GUIDE PLATE
WALL SLEEVE
FIGURE
A Premix - some or all combustion air
is mixed with the fuel prior to reaching
the burner nozzle; in atmospheric
burners, this is usually accomplished
with venturi shaped mixing tubes, and
is limited to mixing primary air only.
Secondary air flows around the venturi
tubes and mixes beyond the burner nozzle
(Figure 4b).
Some mechanical draft burner designs
can also be classed as premix burners,
but most are not. Premix burners are
subject to "flash-back" - the burning of
the fuel/air mixture within the venturi
or mixing chamber.
Atmospheric premix burners can be
arranged to fire either horizontally
(inshot) or vertically (upshot) and are
commonly used in conversion of existing
boilers to gas, where chimney heights
are sufficient to provide the proper
draft. These burners are designed to
operate on low and/or intermediate gas
pres sures.
B The post-mix or non premix burner has
no facility for fuel/air mixing prior to
the burner nozzle; this mixing takes
place in the burner throat and is rapid
enough to permit ignition in the burner
throat. Post-mix burners are not subject
to flash-back, but quite often show signs
of instability if the fuel/air ratio is upset.
These burners are usually mechanical
draft because the turbulence required to
obtain good and rapid mixing must be achieved
by air pressures higher than are normally
-------
c
o
•H
u
2
-------
Natural Gas Fired Installations - - Design Considerations
available from negative furnace pressures.
Post-mix burners are used in low, inter-
mediate and high gas pressure ranges.
Gun type burners and ring burners are
two popular examples of post-mix burners,
and are usually fired horizontally.
Post-mix burners usually offer a fairly
wide turndown range (the ratio of maxi-
mum input to minimum input) because
they are not subject to flash-back, though,
as mentioned earlier, they may become
unstable at one end of the range or the
other.
The subject of turn-down is one which has
often been debated, abused and the term
mis-used. When we speak of turn-down as
it applies to gas burners, we are talking
about volume or burner capacity limits.
Since a burner behaves essentially as an
orifice, its input varies directly as the
square root of the pressure applied to the
burner manifold; therefore, if the pressure
is increased 4 times, the input will increase
the square root of 4, or 2 times. People
have been known to describe burner turn-
down ratios in terms of pressure rather
than volume, and you can see how misleading
this can be; the table below shows several
pressure versus capacity relationships:
if pressure is
increased
by a factor of
2.00
4.00
9.00
16.00
25.00
100.00
burner capacity
increases by a
factor of
1. 414
2.00
3.00
4.00
5.00
10.00
It is also well to remember that burner
turn-down characteristics are only as im-
portant as the need for that turn-down exists.
Some jobs run at reasonably constant loads,
and do not require wide turn-down burners.
Other jobs have widely varying loads and
need burners which can match these loads
and still maintain stable, efficient fires.
If we had for example, a load which went
from its peak down to 1/4 its peak, we
would like to have a burner which could
give us a turn-down ratio of 4 to 1, but
note that this means a pressure variation
of 16 to 1. If our burner provided peak
capacity at a manifold pressure of, say 1. 0
psig, then at low fire the manifold pressure
would be only 1/16 psig or 1 ounce. The
question we need to satisfy ourselves on is
"Can this burner operate in a stable and
efficient manner at these two extremes?"
Burner selection also involves deciding on
how many burners, as well as selecting the
type. Some heat exchangers are designed
with combustion chamber shapes which
cannot be properly satisfied with only one
burner; heat distribution is important to
good heat transfer. A very wide furnace,
for instance, could not be properly fired
with one larger burner; or a very short
furnace may require several small burners
to prevent flame from impinging on the
rear wall. These things are more a matter
of judgement than they are a matter of hard
and fast rules.
The final major consideration in burner
selection has to do with the furnace pressure
against which the burner must operate. In
the case of the atmospheric burner, we must
compare the draft loss of the burner selected
against the available furnace draft; failure
to do this often leads to inadequate burner
input capability. Forced draft burners, on
the other hand must have blowers which
have both the capacity and static capability
required to overcome the draft loss thru
the boiler and breeching. The information
regarding these burner characteristics
should be available from the burner manu-
facturer, and should be checked against
the system requirements.
V Factor 3 - THE EXHAUST SYSTEM
The exhaust system is the third parameter
of our system, and we have already seen
that its characteristics can affect burner
selection.
-------
Gas Pressure
Available
Specific
Gravity
Heat Content
Chemical
Composition
Gas
Supply
Heat Output
Required
Heat Input
Gas Flow
Selection
Burner,
Controls
Operational
•Requirements
Overall Design
and Efficiency
Combustion
Chamber
Size and Shape
Heat Exchange
Surface Area
Heat
Exchanger
Architectural
Consideration
FIGURE 5
-------
Natural Gas Fired Installations — Design Considerations
While the exhaust system is purely the
means by which the products of combustion
are removed from the heat exchanger, the
design of it is as important to system opera-
tion as any other factor.
In considering the design of a new installa-
tion, such factors as architectural consider-
ations, economics of installation and
operation, and the type of boiler being con-
sidered all combine to dictate whether natural
draft or mechanical draft is most desirable.
If, for instance, we have a low profile, one
story building and a pressure fired boiler
(with forced draft burner equipment included),
a short "stub" stack may be all that is
needed to vent the system. On the other
hand, if we have an existing stack which
will deliver the necessary draft under all
operating conditions, we could eliminate
the initial cost and operating expense of
mechanical draft fans, and consider the use
of atmospheric burner equipment.
In between these two extremes we find
cases where we can use an induced draft
fan to provide negative furnace pressures,
and still meet architectural requirements
for low profiles. It is not uncommon to find
installations on which both forced and induced
draft fans are used.
Modern practices have been forcing the
industry more and more toward mechanical
draft equipment in order to satisfy the re-
quirements for packaging, single responsi-
bility, purging, and to provide more
positive control over air flow characteristics.
Since natural draft available from a stack
depends on temperature differences inside
and outside the stack, it is difficult to specify
a definite purge period which would always
meet with approval body requirements,
because stack conditions can vary so widely.
With mechanical draft equipment, you always
have a known amount of air flow for purging,
so you can assign a definite purge period.
A Stack draft determination
When considering natural draft stacks
and their draft capabilities, we have
found that the following approach provides
satisfactory results:
Theoretical draft
(inch, we at sea level)
- 7 6
' 7'6
-------
Natural Gas Fired Installations - - Design Considerations
be adequately braced internally or extern-
ally so as to prevent "drumming" of wide
metal panels. Breechings should also be
insulated to minimize overheating of the
boiler room area and to keep stack
temperatures up, particularly if natural
draft is involved.
The terminating elevation of natural draft
stacks is usually sufficient to preclude
objectionable discharges in the vicinity
of occupied space. Stub stack arid induced
draft fan vent outlets, because they are
so short, often terminate at or below
window or air intake levels and can pose
a problem. Due consideration should be
given to the consequences of such
termination elevations, keeping in mind
that the possibility of control
mal-adjustment could cause noxious
products to issue from the stack.
The normal products of combustion of
a natural gas fired appliance are not
objectionable products and therefore do
not constitute pollutants. This is not to
say that natural gas fired installations
are incanable of contributing to air
pollution, but rather that so long as these
installations are properly controlled and
adequately checked by reliable instru-
mentation, they do not present an air
pollution problem.
B Control and instruments
Finally, then, let us consider what
constitues normal and adequate control
and instrumentation.
Time does not permit discussion of the
safety control aspects of installations
such as we are concerned with, and since
we are centering our attention on the
control of combustion products, suffice
it to say that safety controls are a major
consideration, and that the requirements
for them are well documented by approval
body agencies such as Factory Mutual,
Factory Insurance Association, etc.
VI PROPER OPERATION
The proper operation of a gas fired installa-
tion will include:
A Keeping the fuel supply in proper relation
to the demand;
B Keeping the air supply in proper relation
to the fuel supply.
This can be done either by a man who watches
gauges and flame appearance and adjusts
valves manually according to judgement, or
it can be done automatically; in either case,
the things which must be done are:
1
Regulate incoming gas supply to pro-
vide a constant gas pressure ahead of
the control valve. It is good practice
to use a regulator for each boiler so
that the gas flow to one boiler is not
disturbed as the other one turns on
or off.
Control the gas flow to the burner
through a gas control valve which re-
ceives information regarding the out-
put of the heat exchanger, and adjusts
in direct proportion to that output. On
small installations, say under 100 HP,
this is often done with just an on-off
valve; on larger installations a control
system with a modulating valve is
usually economically justifiable.
Control of the combustion air flow is
accomplished by the manipulation of
dampers either at the outlet of the heat
exchanger, or at the inlet of the burner,
or at both points. On small, on-off
installations this may be accomplished
simply by linking the on-off valve lever
to the burner louver, in conjunction
with a barometric damper in the flue
outlet, or a draft controller which
measures furnace draft and positions
the boiler uptake damper to control the
draft.
12
-------
Natural Gas Fired Installations — Design Considerations
The more elaborate systems, such as
are found on installations of 500 HP and
up, actually meter the fuel flow and
air flow and adjust automatically to
compensate for flow changes.
Failure to maintain proper air/fuel
ratios can lead to or be detected by
the following:
a High excess air - evidences of
which are:
1) Flame extremely blue and "hard"
(lean)
2) Excessive combustion roar
3) Burner vibration, pulsation or
flash back
4) Sharp, acrid odor of "aldehydes"
5) High stack temperatures (normal
boiler temperatures will run
about 125-150°F above steam
temperatures, or from 350° to
550°F).
6) Flame front blowing off burner
nozzle
7) Flame extinction
8) Excessive gas consumption
b Insufficient air - evidences of
which are:
1) Flame extremely rich; will have
orange-red appearance and seem
to roll in furnace.
2) Smoke issuing from stack
3) Soot deposits on heat exchanger
surfaces
4) Burner pulsation
5) Production of carbon monoxide
(toxic and odorless) - incomplete
combustion
6) Flame front leaving burner
nozzle
7) Excessive gas consumption
This is an appropriate point to men-
tion one of the most common causes
of insufficient combustion air, and the
one most often and easily overlooked -
inadequate fresh air openings into the
boiler room. It is not enough simply
to have the boiler room door open to
another room, or to count on windows
being open to the outside. There must
be some permanent provision to assure
that fresh air will always be supplied
to the combustion equipment.
One of the first indications of inadequate
air supply is a hot, stuffy feeling in
the boiler room. It must also be kept
in mind that combustion air flow
through an opening into the boiler room
requires a difference in pressure
across the opening, so the draft system
must be able to overcome this pressure
drop as well as the drops through the
rest of the system. For instance,
openings which provide 0. 50 square
feet for each million btu/hr. of gas
burned will result in a pressure drop
across the opening of approximately
0. 012 in. we; less opening per unit
input will increase pressure drop by
the square of the reduction ratio.
Some of the above effects are recog-
nized by the senses of sight, hearing
and/or smell, while others are best
determined by instrumentation.
Flue gas quality is measured by a
chemical or electrical analyzer which
periodically pulls a sample of flue
products into an analyzing chamber
and measures its characteristics in
terms of CO2, O2 and CO.
Normal flue gas products will contain
from 9% to 11% CO2, and 6% to 3%
O2 and no CO; normally, the higher
the CO2, the lower the O2 content in
a flue gas sample. It is possible.
13
-------
Natural Gas Fired Installations - Design Considerations
however, to be misled by taking a sample of
C02 only; referring to Figure 5a, it can be
seen that the % C02 in a flue gas is at its
peak, or "ultimate C02" when the % excess air
is zero. Therefore, with either an increase
or decrease of combustion air, the % C02 will
go down. Note how it is possible, for instance
to have, say, 8% C02 and still have an air
deficiency. If you had an instrument which
would record % C02 only, you could easily
determine which side of the peak you are on
by taking a second reading after having in-
creased the air; you then know your first
reading was on the wrong side of the peak.
Associated with flue gas analysis is the
stack temperature reading; using the C02
reading, you can determine approximate com-
bustion efficiency, or "flue loss". The
higher the stack temperature for a given C02,
the lower the combustion efficiency. Figure
5b provides a nomograph which can be quite
useful in approximating combustion quality.
Particularly in the case of atmospheric
equipment, another very useful instrument
is a furnace draft gauge, which will indi-
cate the pressure within the combustion
chamber. This reading can be helpful in
avoiding accidental positive furnace press-
ures and can give us forewarning wh°.i some
unknown occurrence has affected our avail-
able draft.
There are other instruments to be sure, but
these plus visual observation are sufficient
to help keep any installation in balance.
VII CONCLUSION
This has been a rather broad coverage of de-
sign parameters for industrial gas burning
installations, with little detail in any one
area. Looking again at the completed block
diagram, Figure 6, we realize that the heat
exchanger and its characteristics, the gas
supply and its peculiarities, the exhaust
system and the control system are all inter-
related and must be considered concurrently
in evaluating the overall installation. With
this observation, we shall have gained an in-
sight that seems to have escaped many engi-
neers for many years.
Ultimate CO-,
% of Flue
Gas Sample
"Perfect"
Combustion
Fuel/Air Ratio
Figure 5A
-------
Natural Gas Fired Installations - Design Considerations
600 _
500 _:
o
o
400— v
300—
250-
in
Oi
OJ
3
200 —
150-
OJ
o
Ol
i-
s_
O)
a.
FLUE HEAT LOSSES - NATURAL GAS
% Flue
Heat Loss
50--
\
V-
15--
Flue Gases
Excess % C02 Air
600—
500-
400—
300-
200-
-1.5
-2
100 —
50-
100—I
Example - Heat loss for flue gases at 400°F
temperature difference above room and 10% 0—
C02 is 19%. Combustion efficiency is 81%
Note - Average dewpoint for flue gas products of
natural gas combustion is 178°F.
;-s
-7
-8
1-9
f-10
-11
-12
Figure 5B
15
-------
Gas Pressure
Available
Specific
Gravity
Heat Output
Required
Heat Content
Heat Input
Gas Flow
Selection
Burner,
Controls
Operational
Requirements
Overall Design
and Efficiency
Combustion
Chamber
Size and Shape
Chemical
Composition
Heat Exchange
Surface Area
Heat
Exchanger
Control
and
Instrumentation
Architectural
Consideration
Induced
e
n
[U.
Q
P
en
5*
01
o
3
en
Q
n
o
3
O
3
FIGURE 6
-------
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 Tacking 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.
jgxternal 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:
J. C. and Skrotzki, B.C. A.,
pp 85-88 (December, 1948).
PA.C.ce.26. 9.66
Rowley, L.N. , McCabe,
'Fuels and Firing", Power,
-------
Oil Burning Equipment
STEAM OR AIR ATOMIZING OIL BURNERS
1
Iteom-e-temlilng burner of external-mixing type, above, bring!
•II end atemlilng medium, steam, together at tha burner tip.
Register, below, hot damper vanos ta rogulate the air supplied
la typical design of Internal-mixing
tomlilng burner, changing tip
|O af capocltl** handled
Oil or far
o III rhlt external-mix all burner
• ileom |et hits th> emerging all
at right angle* at tha all leaves tha
burner; gives turbulent mixing action
4 lew-preuure air larval al
•temlllng medium for thli
burner, meeting ell at tha tip
and breaking It up. Air aloml-
lallen finds relatively little
use because cast 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,
2
-------
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 Jtlochowlcol-oromliing burner rocalvos th« oil vmlmr
prOMOro, ob««r 2)3 !• 3OO p«l, «nd of on optln
vUcoslty *f «b.ot 190 ..« Ortflco •i.mlr.i rh.
g With flmod orifice
•lie, b»«f atoml-
»tl«n occuri in narrow
flow rang*. D.ilgn at
right obtains wld« ca-
pacity rang* by supply-
ing all fa bwrn.r tip
of * constant rat* In
OXCOSl of demand. OH
burned vorlri with fho
lood, r«st If r«nirn«d
7 *•»•»*• control rod, contor, through a rogulatlng
r**"- VOrUl tho aro* of tangential slot! In iprayer
ploto and volumo of oil passing through ortflco, right.
With oil kopt at 300 psi ond 700 «s«, rango Is 10 to 1
Q WMo-rango burn*
Or above operate*
on conitant-dlfforontlal
•yttoms
-------
Oil Burning Equipment
Figure 9. How One Wide-Range
Mechanical Atomizing
Oil Burner System Operates
lua
• «»gvlo ilon of • mpu t frwn tli*
whet* atomising ond whlrltaf «nd
th*wi obov*, can com* fromolthor
c««itant-dlff*r«rttl«l v«lv« »r a
fOflltcitt.dlft.f •ittlal pvmp I. h,U
.tr... mpplr ond i *****
Rotary-Cup Burners. Third major class
of oil burners, the horizontal rotary cup,
atomizes fuel oil by literally tearing it
into tiny droplets. A conical or cylin-
drical cup rotates at high speed (usually
about 3500 rpm if motor-driven). Oil
moving along this cup reaches the rim
where centrifugal force flings it into an
air stream. Fig. 10.
This system of atomizing requires no
oil pressure beyond that needed to bring
oil to the cup, and proves attractive in
installations where only low-pressure
steam is available. High oil preheat
temperatures must be avoided since
gasification may develop. The rotary
cup can satisfactorily atomize oils of
high viscosity (300 ssu), however, and
has a wide range, about 16 to 1.
Fig. 11 shows a burner with a built-in
driving motor, while Fig. 12 shows one
with a belt drive. It also indicates
provision for swinging the burner out of
the furnace.
Gas and oil burners are often combined.
Designs of such combinations vary widely,
both in nature of oil unit and gas unit.
Their ability to handle either of the two
fuels, or both at once, proves desirable
in locations where both are available.
Burner Maintenance. Properly main-
tained, modern oil burner give highly
satisfactory service. For peak perform-
ance, make sure that the burner gets
uniformly free-flowing oil, clear of sedi-
ment that clogs burner nozzles. This
means avoiding sludge build-up in storage
tanks and keeping strainers in good con-
dition. Preheat temperature must be
right for fuel and burner type, and must
be uniform.
Keep burners in good condition by watch-
ing for wear caused by abrasion of ash in
fuel, and for carbon buildup. In rotary-
cup burners, worn rims cause poor atom-
ization. If cups are not properly protected
after being turned off, carbon forms on
the rim. When burner is shut down al-
ways take out the cup and insert a flame
shield. Worn or carbonized mechanical -
atomizing nozzles play hob; replace worn
nozzles and keep them clean.
-------
Oil Burning Equipment
oil swirls
counter clockwise
ROTARY CUP ATOMIZING OIL BURNING
air
oil
10 Cup revolving counterclockwise
breaks up all film at rim by
centrifugal force and discharges
into a clockwise air stream
air
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
-------
FUEL OIL BURNING-DESIGN PARAMETERS
J. Percival*
I. INTRODUCTION
A. Pollutant Information
1. Potential pollutants
Table 1. Potential Pollutants
Emitted Regardless.
of Design
so2
Ash
Reduced
Ry Design
NO
X
so3
Eliminated
by Design
CO
Smoke
Soot
2. Pollutant Emission Rates
For 20,000 Ibs steam/hour (1500
Ibs oil/hour) the pollutant emis-
sion rates are listed in Table 2.
3. Local Nuisance
Acid smuts caused by condensation
of soot plus 803 may cause local
nuisance.
B. Design Parameters l—
1. Overall Purpose
The overall purpose is to generate
hot combustion gases by:
a. Burning fuel completely.
b. Using minimum quantity of air.
c. Discarding flue gas at low
temperature.
2. Requirements for Complete Combustion
a. Fine atomization.
b. Good mixing with air - high
turbulence.
c. Source of continuous ignition.
d. Room to burn - time to burn.
e. No quenching until combustion
complete.
Table 2. Pollutant Emission Rates
Ib/hr
ppm (vol.)
grains/ft3
Pollutants
SO. Ash NO SO. CO Smoke Soot
2 x 3
60 1 10 0.3 0.1 - 0.5-6
1300 - 400 35 50 -
.023 - .01-. H
*ESSO Research and Engineering Company
Linden, New Jersey, February 17-21, 1969
PA.C.ce.43.1.70
-------
Fuel Oil Burning - Design Parameters
II. FUEL OIL HANDLING
A. Fuel Oil Storage
1. Bunkering
Things can happen in the tank
which may affect combustion.
Burners may become plugged by
sludge. Keep sludge suspended in
fuel by CONTROLLED BUNKERING.
Controlled bunkering is the pro-
cess of keeping the stored oil in
suspension as illustrated in
Figure 1. The incoming fill scours
the floor and resuspends the sludge.
Pour Point
Pour point can be important, but
the smaller installations will
always use 60°F pour fuel. Pour
point is the lowest temperature
at which an oil flows under stand-
ard conditions.
110° f Pour
OUTLET
RETURN
STEAM COIL
FILL
off
tS°f 110" F
Temperature
Figure 1. Controlled Bunkering
2. Heating
Stored fuel should be heated to
pumpable viscosity.
Easily Pumpable
5000 SU*
Just Pumpable
25,000 SU*
*6 Oil 90-100°F 70-80°F
#5 Oil 60-70°F 50°F
*Saybolt Universal - Viscosity as measured
by a standard orifice
Figure 2. Pour points of two oils of same grade,
B. Pumping and Heating
1. Pumps
Two pumps may be required if:
a. distance from tank to burner
is over 100 feet,
b. several burners are fed by
common line.
2. Heaters
a. Steam or hot water heat
exchangers.
b. Electrical heaters for final
heating.
T = transfer pump
B = burner pump ( often an
integral component of
the burner )
S = strainer
HT0
Figure 3. Pumping and Heating Systems
-------
Fuel Oil Burning - Design Parameters
100 190 200 250 300 330 400-
A = steam atomizing
B = pressure-jet atomizing
C = rotary cup atomizing
Figure 4. Atomizing characteristics of
different burners - distribution
of droplet size
III. BURNERS
A. Atomization
Fuel oil must be vaporized to burn.
Idea is to provide a large surface.
Size of droplet is function of vis-
cosity, fuel oil rate and energy in-
put, e.g., a formula applying to pres-
sure atomizing burners is:
SMD = 160
where: SMD
M'16V22
.42
Sauter mean diameter,
micron
Micron = 0.001 mm.
M = fuel rate, Ib/hr.
V = viscosity, SUS (Saybolt
Universal Seconds).
P = gauge pressure, psig.
Viscosity is controlled by preheat.
Energy input may come from oil pres-
sure, a second fluid moving at high
velocity, or a centrifugal force.
Distillates
O
o
Residual fuels
O o o 00
Figure 5. Mode of Combustion of fuel
oil droplets
1. Smoke
Submicron particles of graphitic
carbon formed from the gas phase
and preserved either:
a. By overall lack of oxygen.
b. By premature chilling of flue
gas.
2. Soot
a. Originates as carbonaceous
cenospheres, ash plus carbon.
b. Will burn out to ash given
time and temperature.
c. Size 10-40 microns plus some
much larger if atomization is
poor.
B. Burners - Atomizers
1. oil inlet
Figure 6. Simple pressure-jet atomizer
1. oil inlet
2. spill return
Figure 7. Spill pressure-jet atomizer
1. Pressure Atomized Gun Burners
a. Atomizing energy comes from
pump pressure.
b. Output increases with square
of pressure (simple type).
-------
Fuel Oil Burning - Design Parameters
tangential
slots
swirl orifice
chamber
low fire
high fire
450 Ibt
250 Ibt
450 Ibs
445 Ibs
Figure 8. Piping arrangement for spill-back pressure atomizer
of back pressure (spill type).
ity - increased viscosity
causes increased throughput
until the air core chokes.
•
fi=S
Y Jet &&
^3^2.
n
— c
~»
^
^f
g
3
•
_
<
•
^
V
•i
Lr-
je
E
&•
-u_
fa
^~ 2
<«- 1
a. Large turn-down without sacri-
fice of atomization.
b. Only moderate pump pressure
required on oil.
c. Less vulnerable to dirt in oil
than other types.
d. Good atomizers on clean fuel
use only 0.1 Ibs of steam/lb
of oil but consumption may
rise to 1 Ibs/lb if poorly
adjusted.
e. Steam used at burners repre-
sents heat lost.
f. Steam effects a final preheat
within the burner.
1. steam inlet
2. oil inlet
or air
Figure 9. Steam atomizers
-------
Fuel Oil Burning - Design Parameters
3. Air Atomized Burners
Similar in principle to steam
atomizers but a large volume of
low pressure 0.5-2.0 psig air is
used.
oil -*
mounting hinge
motor
Figure 11. Rotary cup burner
Figure 10. Air atomizer
The amount of air used for atom-
izing is only a fraction of the
total air required for combustion,
e.g.,
Total Air Air to
To Burn 1 Gallon Atomize 1 Gallon
1700 SCF
80 SCF
Nevertheless, combustion begins
sooner and finishes more rapidly
than with any other type of
burner - shorter flame.
4. Rotary Cup Burners - Centrifugal Burners
a. Cup revolves at 3600 rpm. Throws
a sheet of oil from its periphery
which is shaped into a cone by the
primary air nozzle.
b. Sizes range from 3 gph - 300 gph.
c. Oil flow controlled by metering rate.
d. Principle fault from air poll-
ution point of view concerns
vulnerability of edee^f cup to
accidental notching. Compare
with action of a weir. Local
high flow at the notch produces
some very course droplets.
Table 3. Comparison of Operating Conditions
Burner Type
Pressure Atomizing
Steam Atomizing
Air Atomizing
Viscosity at Burner
SU
150
180
to
400
80
°F for No. 6
210
200
to
170
240
Pressure PSIG
Oil
200
to
1000
10
to
150
30
Steam
40
to
175
-
Air
_
1.5
-------
Fuel Oil Burning - Design Parameters
oil
air or steam*-
oil
Figure 12. Sonic Atomizer
sonic waves
chop oil
5. Sonic Atomizers
a. Sound frequency 10-20,000 cps.
b. Sizes range from 10 gph - 1000
b. Natural Draft or induced draft:
AP - P (Atmosphere) - P ( furnace)
2. High pressure drops are used with
narrow throats. Low pressura drops
are used with wide throats.
3. Design maximizes relative velocity
of ait and fuel - potential energy
of AP is converted to swirl and
turbulent flow. High mixing energy
results in a short flame and saves
size of combustion space, but
costs fan power.
4. At low firing rate the velocity
of the air will be reduced in pro-
portion with the fuel rate. Mix-
ing is optimum at high fire. At
low fire it is usual to compensate
by using more excess air.
c. Almost any gas can be used to
drive the sound generator -
air, steam, oxygen, propane, etc.
d. About 1 pound of air will atom-
ize 5 pounds of oil.
e. Burner is self -cleaning.
IV. AIR/FUEL MIXING
A. Mixing Air with Atomized Oil
1. Energy for mixing comes from the
pressure drop across the burner
register.
a. Forced Draft: AP - P (Windbox)-
P (furnace)
adjustable
registers
oil-*1
wind
air -*\box
air
def1ectors
B. FUEL/AIR RATIO CONTROL
The purpose of fuel to air ratio con-
trol is to insure sufficient combus-
tion air at all imput rates of fuel.
1. Continuously Modulating (e.g.,
"Steam Flow/Air Flow")
a. Change in steam flow signals
for corresponding change in air
flow. Fan louvers adjust or
fans change speed.
b. Change in steam pressure which
accompanies the change in flow
actuates change in fuel input .
Weakness of this system is that
oil change is accomplished
faster than air change.
(1) . On a falling load a period
of high air and low fuel in-
put occurs.
(2) . On a rising load a period of
high fuel input and low air
rate occurs.
The system must be adjusted not to
smoke during the latter (2) mode. In
general, this calls for more air than
is necessary at the steady mode.
A better system (but more expensive)
is one which signals and controls fuel
flow and air flow together, with an
overriding control on the fuel signal-
-------
Fuel Oil Burning - Design Parameters
- VE
NATURAL
DRAFT
- VE
ID
INDUCED
DRAFT
FD:O
windbox
VE
FD
FORCED
DRAFT
( PRESSURIZED
ZERO
ID
BALANCED
DRAFT
windbox
Figure 13. Air handling systems
led by a continuous oxygen analyser.
A fast system of flue gas sampling
and analysis (by paramagnetic oxygen
meter) is required with this system.
Most oxygen meter systems have a slow
response rate.
2. STEPWISE MODULATION
Stepwise modulation is more common
on commercial burners - e.g., apart-
ment houses, small boilers, etc.
Oil input is controlled by pressure
which can assume any of tvo or three
preset levels. Air shutter is
positively connected to the oil
control and assumes corresponding
positions instantly.
Overall master signal may origin-
ate from thermostats, steam pres-
sure signals, etc. Start up se-
quence will move automatically
through low fire, medium fire and
high fire positions. The preset
modulation is set up on:
a. A clean burner of given
throughput.
b. A given grade of oil at
a given preheat.
c. A clean set of air shutters.
These conditions must be maintained
for satisfactory operation. Major
changes (e.g. of oil type) call for
readjustmenti
C. AIR HANDLING SYSTEMS
V. IGNITION
High intensity flames would blow off the
burner if a source of continuous ignition
were not present.' Three principal sources
of continuous ignition are: (1) hot re-
fractory burner block, (2) "diffuser"
bluff body creates stagnant pockets of hot
gas near point of atomization, and (3) re-
turn flow of hot gas. See Figures 14 and
15.
VI. HEAT EXCHANGE
In the larger power station boilers about
half the heat in the fuel is given up in
the RADIANT section; the other half in the
CONVENTION section.
A. FURNACE AND SUPERHEATER
The temperature to the inlet of the
furnace is the theoretical flame tem-
perature, which is never attained in
-------
Fuel Oil Burning - Design Parameters
Figure 14. Dish stabilizer
Convection
Figure 15. Swirl flow stabilizer
flue gas to stack
-------
Fuel Oil Burning - Design Parameters
Table 4. Temperatures in Boilers
Section
Furnace (Radiant Section)
Superheater
Economizer
Air Heater
>
(Convection
Section)
Temp . In Temp . Out AT
3600°F 2000°F
2000°F
900°F 600°F
600°F 350°F
1600
> 1650
fact for two reasons: (1) the flame
begins to radiate heat away to the
furnace walls before combustion is
complete and (2) combustion will not
go to completion at very high tempera-
tures because of dissociation,
2CO,
2CO + 0,
In general, the smaller boilers have
proportionately less radiant section
and more convection. For this rea-
son the temperature of combustion gases
leaving the furnace of a smaller
boiler may be considerably higher than
2000°F.
Furnace temperatures are also a func-
tion of the amount of excess air em-
ployed, the rate of firing, the pro-
portion of the furnace wall which is
covered by water tubes as shown in
Figure 17 which applies to a marine
boiler.
In a boiler making superheated steam,
furnace exit temperatures must be
known accurately in order to design
the convection section. The combina-
tion of flue gas temperature available
and steam temperature required governs
the selection of tube materials for the
superheater.
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output ft absorbing surface per hour of full output
0
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Figure 17. General effect of excess air (diagram a), ratio of heat absorbing to refractory surface
(diagram b), and firing rate (diagram c) on furnace heat absorption and temperature.
Based on 18,500 BTU fuel oil.
-------
Fuel Oil Burning - Design Parameters
GAS I INLET
__ AIR
OUTLET
GAS OUTLET
GAS DOWN-FLOW
AW AND GAS COUNTER-FLOW,
SINGLE-PASS
AIR INLET
GAS UP-ROW
AIR COUNTER-FLOW. THREE-PASS
GAS UP AND DOWN-FLOW
AIR COUNTER-FLOW. SINGLE PASS
GAS INLET
INUT
GAS
GAS UP AND DOWN-FLOW
AIR COUNTER-FLOW, SINGLE-PASS
GAS UP-FLOW
AIR COUNTER-FLOW. THREE-PASS
GAS OUTLET
GAS DOWN.HOW
AIR PARALLEL-FtOW. THREE-PASS
Figure 18. Some arrangements of tubular air heaters to suit various directions of gas and air flow
A knowledge of furnace temperature is
less important in boilers which make
saturated steam in which all of the
heat exchanger surface is backed by
water or water/steam emulsion.
B. ECONOMIZERS AND AIR HEATERS
In low pressure boilers with an econo-
mical amount of heat transfer surface,
flue gas can be cooled to 400°F or
less as it makes its final pass over
the steam generating surface.
In high pressure boilers, particularly
when the steam is superheated, the
temperature of the flue gas is still
high when it leaves the last bank of
•steam generating or superheating tubes.
It is usually economical to build
additional heat absorbing surfaces to
take out some of this heat by using:
(1) economizers to heat up boiler
feed water and (2) air heaters to heat
air which is routed to the windbox by
a F.D. fan. Either or both can be
used to extract heat from the final
flue gas.
Major point of concern with these
pieces of Cold' End Equipment is the
potential problem of sulfuric acid
condensation on surfaces cooler than
the Acid Dew Point. This causes (1)
corrosion and (2) accumulation of soot
and ash particles. Available heat in
flue gas is less at low loads. Some
air may have to bypass the air heater
to avoid chilling the metal below the
dew point.
»*l
e
>10
to
" •
"QJ
£*
s<
u
fea
o.
0
1
Figure
i*
/
S
s
s
s^
/
s^
^
10 200 300 400 300 MO
L combustion air temperature, F
19. Order of improvement in efficiency
when heated combustion air is used
in boiler units
10
-------
Fuel Oil Burning - Design Parameters
light wind
strong wind
effect of buildings
Figure 20. Plume rise
VII. OTHER CONSIDERATIONS
A. Breeching and Stack
Problems with final ductwork and stacks
are similar to those encountered in air
heaters. They are all connected with
the potential deposition of sulfuric
acid and its corrosive and "fly-paper"
properties. Ideal design requires that
(1) the temperature of all inner sur-
faces of the ducts be above the acid
dew point at all loads. (2) the exit
velocity be sufficiently high to pro-
mote plume rise in all winds, and
(3) the height be sufficient to dis-
perse the flue gases efficiently,
particularly that it be high enough
to avoid downdrafts caused by neigh-
boring buildings.
Modern design exit velocities are of
the order 40-60'/sec. at full firing
rate.
A good rule of thumb for stacks in
the vicinity of buildings is that
they should be 2-^ times as high as
the buildings. Several mathematical
formulae have been developed to pre-
dict what height of stack is required
to guarantee a safe maximum concen-
tration of S02 at ground level. Some
of these are compared in Figure 22
which relates to 3% sulfur in fuel and
a required maximum ground level con-
centration (GLC) of 0.2 ppm S02-
HIGH FLUE GAS DISCHARGE VELOCITIES ARE
NECESSARY TO AVOID DOWNWASH
50 -
30
bj
020
ZONE OF ZERO DOWN WASH
AND OF DOWNWASH LESS THAN
ONE CHIMNEY DIAMETER BELOW
TOP OF CHIMNEY
ZONE OF
DOWNWASH
APPROX ONE
DIAMETER
BELOW TOP
OF CHIMNE
ZONE t F DOWNWASH
XCEEDING ONE CHIMNEY DIAMETER
BELOW TOP OF CHIMNEY
(MECHANICAL ENGINEERING, JUNE 1940)
10 15 20 25 30
WIND VELOCITY. MILES PER HOUR
High flue gas discharge velocities are
necessary to avoid downwash
Figure 21.
11
-------
Fuel Oil Burning - Design Parameters
i
* 30 50 100 300 500 10 O
Flue gas output Nm3/sec
Figure 22. Predicted stack height requirements
Once a plant is built, fairly major
changes are required to alter either
the gas velocity or the gas tempera-
ture in the ductwork and stack.
B. MATERIALS OF CONSTRUCTION
1. Firebox Refractory. High alumina
firebox to withstand attack from
oil ash.
2. Steam Generating Tubes. Usually
low carbon or medium carbon steel.
3. Superheater Tubes. Stainless.
Chromium alloys or nickel chrome
depending upon temperature.
4. Economizer. Originally cast iron
to resist conversion from 0. in
boiler water. Now low carbon
steel with de-aeration of feed-
water.
5. Air Heaters. Mostly low carbon
steel but low temperature parts
may be stainless; ceramic and even
glass has been employed.
6. Stacks. Masonry lined with acid
res-istant brick and mortar, masonry
liner supported within a concrete
outer stack with a heat insulating
cavity between, steel liner welded
and supported within a concrete
outer stack (recommended for stacks
which are under positive pressure).
C. INSTRUMENTATION REQUIREMENTS
1. Draft controls.
2. Low water cut off.
3. Light up sequence controls.
a. purge with air
b. light and prove pilot
c. light and prove burner
4. Flame failure control.
5. Air/fuel ratio controls.
6. Steam temperature control.
7. Oxygen analyser. (Sometimes CO/H
analyser).
8. Smoke recorder. (Only instrument
which is connected directly with
air pollution control).
D. INFLUENCE OF FUEL OIL TYPE ON DESIGN
PARAMETERS
1. Distillate Fuels
a. Require somewhat less combus-
tion space to burn completely
than do residuals.
b. May be burned at small burners
down to 0.5 gallons/hour.
c. Generally need no preheat.
2. Low Sulfur Fuels
a. Permit design of lower cold
end temperatures.
b. May permit some savings on
superheater materials.
3. Low Ash Fuels
a. Permit closer spacing of tubes
in convection section.
12
-------
Fuel Oil Burning - Design Parameters
Table 5. Safe Maximum Temperatures (Oxidation Resistance Basis)
Material
Carbon steel
Carbon-Moly.
Croloy 1/2
Croloy 1 1/4
Croloy 2
Croloy 2 1/4
Croloy 3M
Croloy 9M
Croloy 18-8 Ti
Croloy 18-8 Cb
* Of surface in contact with
** Temperature limit may be
and other circumstances.
ASME
Specification
SA-210
SA-209 grade Tla
SA-213
SA-213 grade Til
SA-213 grade T14
SA-213 grade T22
SA-213 grade T21
SA-213 grade T9
SA-213 grade TP321
SA-213 grade TP347
flue gases.
modified depending on character
It can be 100 to 200F higher in
pressure process steam superheaters fired with low sulfur
*
Maximum
Metal
Ter.p F
950
975
975
1050
1080
1100
1125
1200
**
1400
**
1400
of fuel
low
fuel.
13
-------
PAGE NOT
AVAILABLE
DIGITALLY
-------
FUEL OIL BURNING
GOOD OPERATION PRACTICES
J. Percival *
I. INTRODUCTION
Ideal operation occurs when (1) all carbon
in the fuel is burned to CO.. (2) a minimum
quantity of the sulfur in the fuel is burned
to SO-, and temperatures are arranged so that
only a minimum amount of sulfuric acid is
deposited in the cold end, and (3) a minimum
quantity of nitric oxide is formed. All of
these are affected by the amount of combustion
air employed.
Production of SQj and NO are reduced at
low excess air. Smoke is generally reduced
by using higher excess air. Soot is com-
plicated but there is usually an optimum
amount of excess air for minimum soot.
II. OPTIMUM COMBUSTION AIR
The theoretical quantity of air needed to
convert fuel oil to CO. and H.O is given by
the following:
Total theoretical air requirsment of such an
oil is:
Ibs Air/lb Fuel
11.52 x wt. fraction
carbon
+ 34.56 x wt. fraction
hydrogen
+ 4.30 x wt. fraction
sulfur
Alternatively:
% H£ • 26 - 15 x specific gravity, and
% C - 100 - & hydrogen +% sulfur +
water + sediment).
A common type of //6 fuel oil has the following
analysis:
% Carbon
% H.
2
% S
% Water
% Sediment
86.4
11.3
2.0
0.2
0.1
ESSO Research and Engineering Company
Linden, New Jersey, February 17 - 21, 1969
11.52 x .864
34.56 x .113
9.95
3.90
4.30 x .020 = .09
13.94
13.94 Ibs air/lb oil.
s
12.6
12.4
12.2
12.0
11.8
as 11.6
+J 11.4
4-1 11.0
£ 10.8
0 10.6
U
c 10.4
111
C" 10.2
o
-a 10.0
^ 9.8
9.6
9.4
9.2
9.0
8.8
8.6
8.4
8.2
8.0
Figure 1. S
i
pec. gravity @ 60 F (15.6 C)
1.07 1.05 1,03 1.01 .99 .97 .95 .93
f
/
/
1
I
J
f
f
f
I
I
t
/
I
/
/
\
/
/
(
1
2 4 6 8 10 12 14 It 18 20
API gravity
lows the % hydrogen in fuel oil
f the API gravity is known
PA.C.ce.44.1.70
-------
Fuel Oil Burning, Good Operating Practices
If, in fact, 17 Ibs of air is employed in a
real combustion process, the amount of excess
air la:
17-13.94 • 22X
13.94
There is, of course, no need to measure rates
of air flow to know how much excess air is
being used.
An analysis of the flue gas for either
CO. or 0. can be correlated with the excess
air.
Thus, for the type of fuel oil under
discussion:
Flue Gas Analysis
co2z
o2%
16.2
15.7
15.3
14.7
13.5
10.7
7.8
0.0
0.0
0.6
1.0
2.2
3.7
7.2
10.7
21.0
Excess Air
0.0
3.0
5.0
10.0
20.0
50.0
100.0
Infinite
III. SMOKE
A. Formation of Smoke
Smoke consists of sub-micron particles
of carbon formed by:
1. An overall lack of oxygen - e.g.
by using less than the theoretical
requirement of air.
2. Insufficient mixing of air and
fuel even though the air is
theoretically sufficient.
3. Prematurely chilling a partially
burned mixture.
4. Burning with too much air.
Notes (2), (3) and (4) are respective-
ly examples of insufficient turbulence,
time and temperature.
B. Smoke Measuring Instrument
Standard Instrument for measuring
smoke is Bacharach Smoke Tester.
O lodioroch Initruminl Co.
PilHburgh, P.. Ii2J«
Figure 2. Bacharach Oil Burner Smoke Scale
air shutter
^"1A(
air cone
Figure 3. Small furnace burning distillate
fuel
2
-------
Fuel Oil Burning, Good Operating Practices
Table 1. Typical smoke/C02 correlation for a domestic burner
CO,, % Excess Air
14 10
11 40
10 50
9 60
6 140
Smoke No.
9 +
6
2
0
Yellow
Stack Appearance
Smoke Visible
Not Visible
Not Visible
Not Visible
Thin Vapor Visible
Flame Appearance
Long and Dark
Long and Dark
Long and Clear
Shorter
Very Short and Noisy
Table 2. Some typical excess air levels in various types of
equipment (at zero or minimum smoke)
Type
/&_
Home Heat
Apartment House Boiler
Ship's Boiler
60 MW Power Station
Heat Input to Furnace
-,168 Btu/hr
0.18
2.2
80
600
Excess Air %
40
27
15
3
C0,%
11
13
14
15.7
L.-
Table 3. Volumetric heat release rates
Tape
Home
Apartment
Ship
Power Station
Volumetric heat release rates BTU
input/ft combustion space/hour
340,000
100,000
70,000
20,000 to 40,000
Residence time
seconds
0.13
0.50
0.80
2.2 to 1.1
C. Smoke Control in a Small Furnace
Burning Distillate Fuel
A domestic burner may have smoke and CO.
readings shown in Table 1.
The performance of such, a burner might be
improved by using a smaller air cone which would
employ the available fan pressure to promote
better mixing.
Since these burners are practically
unattended and since lint accumulation can
build up on the air shutter ports in the
course of a season, they should not be set
for maximum thermal efficiency.
Some give-away of C02 must be allowed.
The formation of SO. and NO is quite small
regardless of excess air level.
D. Smoke Control in Larger Units
Some typical excess air levels in various
type of equipment at minimum smoke are given
in Table 2.
It would seem that the larger the unit the
less excess air is needed. Compare the
volumetric heat release rates of the different
types of units (see) Table 3.)
Note that the residence time (the time avail-
able for combustion within the high temperature
-------
Fuel Oil Burning, Good Operating Practices
environment) is longer when the heat input
rate/ft3/hr is smaller.
Why are the larger units designed to
have more residence time (large volume/unit
of fuel rate)?
e.
1. Possible to accomodate a second fuel,
g. pulverized coal.
2. Directionally because heat input is
limited by the ability of the combustion
chamber walls (steam generating tubes) to
absorb heat. Usual rate is 50-100,000 Btu/sq.
f t/hr
For similar shapes, large furnaces have pro-
portionately less wall area per unit volume.
Some designers place curtain walls between
columns of burners to get increased area.
IV. LOW EXCESS AIR
A.
Resume of Factors Affecting Ability
to Operate at Low Excess Air
In general the fuel/air mixture must he
fully combusted before It leaves the
furnace zone, because once it leaves
that zone its composition is virtually
frozen. For the same reason, the
flame must not impinge on the furnace
walls.
Thus the optimum conditions are those
which fill the furnace with flame at
high fire, so that the tips of the flame
extinguish Just short of the exit (screen
tubes). If this condition cannot be met,
one or more of the following steps must
be taken:
means narrowing the throat or intro-
ducing a swirl impeller).
(1) and (2) above are available to the
operator within the limits of design and
the demands on the unit. (3) and (4)
represent minor changes of design which
should only be tried in consultation with
the boiler supplier, (j) represents a
major upgrading of the design which must
be accompanied by suitable modification
of the air register to convert the press-
ure energy to mixing energy.
1.
2.
3.
4.
5.
Increasing excess air shortens the
flame.
Lowering the firing rate shortens
the flame.
Adjusting the position of the burner
within the throat of the air register
may shorten the flame but beware of
impingement on the burner block.
Changing to a wider angle nozzle
may shorten the flame, but again be-
ware of impingement.
Increasing the wlndbox/furnace
differential pressure shortens the
flame if the increased energy can
be converted into turbulence. (This
enlarged view of
perforated disc
1. atomizer
2. primary air
3. perforated disc, limiting
primary air velocity
4. secondary air
Figure 4. Oil burner with steam atomizer
Based on 7.46 Ib theoretical air
plus 16% excess air (total 8.65
Ib of air) per 10,000 BTU of oil
as fired
tar burner tKrooi diom«<*r o< thown
1200 1600 2000
Figure 5.
Ib of oil per burner per hour
Air resistance for typical marine
oil burners
-------
Fuel Oil Burning, Good Operating Practice
Effect of fuel sulfur and excess air
on acid dewpoint
200
Fuel sulfur content % wt.
- 122
Figure 6. Effect of fuel sulfur and excess air on acid dewpoint
THEORETICAL DEW POINT SOS RELATIONSHIP
ses
300
273
-------
Fuel Oil Burning, Good Operating Practice
3-0
BOILER DATA
BOILER 02 16%
LOAD 34.000LBS FUEL/HR
ATOMISING PRESSURE 400 PS.I.
4.5% SULFUR FUEL
TOTAL DEPOSIT LINE
"•y .
IN
ACID DEPOSIT
CONTAINING FREE
SULPHURIC ACID WATER
AND CARBON
LIMITING SURFACE TEMP
/BELOW WHICH ACID SMUTS
CORROSION PRODUCT
AS SULPHATE
(80 200
220 240 260 280
SURFACE TEMPERATURE, °F
300 320
Figure 8.
Surface temperature and boiler oxygen control the formation
of moist deposits
-------
Fuel Oil Burning, Good Operating Practice
J£.\J
300
280
260
„- 240
UJ*
Of.
3
£220
Q.
S
UJ
t—
o 200
<
u.
Of
•ft
180
160
140
120
CONDITIONS
FOR DRY SURF/
iCES
WITH NO ACID DEPOSIT s
/
-/
A
/
A/VAA
X^
X
OEPOSI
INCREA
J- U
^ CONDITIONS FOR MOIST ACID
/. DEPOSITS
1 INCREASE
— 'A- A
/
A
/
/
/
/
A
.s*
s~
TC
SE
DEPOSIT
1.0
2.0
BOILER OXYGEN
3.0
4.0
Figure 9. Relation between surface temperature and acid deposit formation
-------
Fuel Oil Burning, Good Operating Practice
B_ Eenefita of Low Exceas. Air Operation
1. Increased thermal efficiency.
2. Lower acid dew point.
3. Lower rates of corrosion of
superheaters.
4. Less opacity of stack plume if
caused by SO-.
V. ROLE AND RATE OF SULFUR IN FUEL
Most of the sulfur burns to SO. which
exits at the stack. A small percentage
(0-3%) burns to SO^. The amount depends
on the level of sulfur in the fuel but
more upon the amount of excess air used.
The following diagrams explain the
situation (see figures 6,7,8, and 9).
Good operation requires that minimum conden-
sation of sulfuric acid occurs on any surflce
because: (1) the material will be corroded and
(2) the moist surface will act like a fly-paper
and will collect solids. The sulfuric acid
problem may be handled by (1) burning a very
low sulfur fuel (less than 0.5% S) (2) burning
with very little excess air (preferably less
than 3%). (3) keeping all critical surfaces
at a temperature above the acid dew point, (4)
neutralizing the SO^ with additives.
VI. COLD END TEMPERATURE CONTROL
A. Economizer
Minimum surface temperature is a
function of the boiler feedwater
temperature - usually above the acid
dew point in power boilers.
Proper draft
B. Air Heater
Average surface temperature is
approximately the mean between the
flue gas temperature and the air
temperature. Efficiency of heat
exchange must be sacrificed to insure
low corrosion rates and cleanliness
of the coldest parts af the exchanger:
1. Part of the cold air may be by-
passed.
2. Parallel flow may be used in place
of the more efficient counter flow.
3. A steam heater may be used to pre-
heat the air before it contacts
the air heater proper.
The last method is often acceptable
where LP steam is available from
a turbine. The loss of efficiency af
the boiler is very nearly compensated
by the increase in efficiency of the
turbine.
C. Breeching and Stack
Whatever heat remains in the flue gas
as it leaves the final heat exchange
surface should be preserved as the
gas travels to the top of the stack.
1. Insulate
2. Avoid leaks and (check C0? level
along breeching and in stack, and
search out and seal leaks if CO,
is not constant).
High draft
Figure 10. Effect of draft
-------
Fuel Oil Burning, Good Operating Practice
VII. ACID SMUTS
A. Formation of Acid Smuts
1. Checking atomization - grade of
fuel, preheat, condition of
atomizer (particularly spinning
cup).
2. Checking draft.
One of the most common faults of
boilers in high-rise apartments is
too high a draft.
High draft effectively reduces the available
combustion space, and draws the flame away
from the refractory. Check for reduction
of soot formation with sticky slide (contact
adhesive attached to steel holder) at breech-
ing or roof level.
Acid smuts are the product of soot parti-
cles which have adhered to and agglomerated on
moist acidic surfaces, and which have sub-
sequently lifted off that surface and become
airborne. The black agglomerates so formed
tend to fall to ground within a few stack
lengths. The local nuisance caused thereby is
particularly noticeable when a boiler is
started up after shut-down.
If the temperature of cold end surfaces
is above the acid dew point, smuts cannot form.
In that case the soot particles will remain
separate and will diffuse widely with the
effluent plume.
Alternatively, if the fuel is. burned
completely to ash, smuts will not form.
•:: . - y-'4
.... .:':i.
.':• '•*-
> ^. .;*
* +-*V-^
* ••.-. •*"
*:**:;;*: *^^ll*i;iili?|iil^ *; ;* ,. "* ..: ? \ \
•• " ^®^lil|illl|l::it !i'^*;Siiil
" * • » .". • •">•*•• *., .*: ..'•-" * " * * ''. ' '
representation of slide with soot
representation of a slide with smut
Figure 11. Study paper slides of soot and smut
The following actions may all help a
smut problem:
1. Insulate the stack - particularly
useful on bare steel stacks - alum-
inum shrouds have been employed.
2. Seal air leakage at the breeching.
3. Operate at very low excess air.
A. Employ an additive (such as MgO or
dolomite).
5. Improve the combustion to minimize
the production of soot particles.
6. Burn distillate fuel which makes
practically no soot.
Note that (3) and (5) may be mutually
exclusive, but not always so (see next
section).
B. Particular Case of Boilers Fired
Intermittently e.g. apartment houses
small industries
In cases where boilers are fired in-
termittently it may be quite impossible
to prevent the deposition of some
acid in the stack. Some draft re-
gulators operate by dumping cold air
to the breeching, and chimneys, which
handle intermittent firing, oscillate
in temperature above and below the dew
point. Best approach is to reduce
formation of soot particles (cenospheres)
to a minimum by:
Correcting the draft to manufacturer's
specifications usually allows operation
at lower excess air.
Table 4. Case history of a 20 gph fire tube
hot water boiler
As found
Reset to
specifi-
cations
draft
0.22"
0.06"
CO 2
10.5
13.0
Smoke #
6
2
soot
much
trace
-------
Fuel Oil Burning, Good Operating Practice
Vint lint
Diungtging tank
/tttardtr txfi
Stationary soot blowers employing straight
nozzles clean banks of in-line tubes. With
staggered tubes, the nozzles are offset for
improved penetration
DittrilHiten
Lift tint-'
Turning rents
Collating hopftr
rtoroft toft*-
Shot cleaning technique calls for cascading
metal balls on to heating surfaces. The
cycle is automatic, utilizing pneumatic lift
Retractable blower lance, driven by two motors,
traverses boiler at one speed, retracts at twice
that speed. Result: about a 25% saving in clean-
ing time and in blowing medium. Speed of lance
rotation is held throughout the cycle
Figure 12. Methods of soot blowing
VIII. SOOT REMOVAL
Large vacuum cleaners are employed to
remove soot from small boilers. This does
not get into the atmosphere.
Large equipment employs soot blowers,
usually steam operated or sometimes by com-
pressed air. Shot cleaning has been employed
in certain types of air heaters.
Solids from soot blowing operations end up
in the atmosphere. The amount is usually a
small percentage of the total solids which are
voided in the course of a day but "since it is
concentrated in a short span of time it is very
noticeable to the public".
Permitted levels of particulates emission
from stacks are becoming tighter.
Table 5 gives some examples which were
in force in 1965.
(Typical particulate loadings for large
oil fired boilers are shown in Figure
13.)
The old ASME figure Q.85/lba/lQO.O lha
of flue gas and the New York figure of Q.33
Ibs/million Btu input are compared below:
ASME
New York
% Fuel
Unburned
1.60
0.57
Grains scf
0.46
0.17
No difficulty should be experienced in meeting
these requirements with normal, well adjusted
oil fired equipment. These levels may be
exceeded for short periods of time (less than
one minute) during soot blowing.
10
-------
Fuel Oil Burning, Good Operating Practice
Table 5. Particulate emission standards in combustion flue gases
City or Organization
Pounds of particulate matter per 1,000 pounds
of flue gas (corrected to 50% excess p.ir, or
12% Carbon Dioxide)
American Society of Mechanical Engineers
(1949 Model Smoke Code)
ASME proposed draft of Nov. 1962
Sparsely settled areas
General city usage
Cities where better conditions are
feasible and required by residents
Provincial and City By-Laws
Metropolitan Toronto
Alberta
Manitoba
Chicago
Los Angeles County
New York
(a) Refuse burning equipment
(b) Fuel burning equipment
Capacity rating, BTU,
10 million or less
50 million
100 million
500 million
1,000 million
10,000 million or more
0.85
0.80
0.65
0.50
0.85
0.85
0.68
0.60
0.52
0.65 (top limit of
250 Ibs. per hr.)
Ibs./million BTU, Input
0.5
0.38
0.33
0.25
0.22
0.15
IX. OPERATION AT VERY LOW LOADS
A. Effects of operation at very low loads
In general combustion conditions are
optimum at the rated design loads, and some
deterioration of conditions has to be accepted
at lower loads when:
1. Temperature in the furnace zone is
lowered.
2. Quality of air/fuel mixing deteriorates
due to lower windbox/furnace different-
ial pressure, and consequently lower
air velocities at the throat.
3. Atomization deteriorates:
a. Especially with simple pressure
jets.
b. Less so with spill jets, steam or
air atomizers.
4. Percent excess air usually has to be
raised:
a. To compensate for poor air/fuel
mixing.
b. To maintain steam temperature
(if superheated).
5. Air in-leakage at breechings, etc.
becomes proportionately increased.
11
-------
Fuel Oil Burning, Good Operating Practices
B. Results
As a result of above factors, thermal
efficiency ia reduced and production of soot
and acid smuts (per pound of fuel consumed)
ia likely to be greater at low load. Where
there ia a choice:
1. Shut down some burners in a multi-
burner unit and fire the remainder
near full throughput.
2. Where there are several boilers to
carry a load, work two boilers at half
load rather than four at quarter
load - better still, one at full
load (but generally the operator will
require some spare capacity to be in-
stantly available).
X. CARBON MONOXIDE
Carbon monoxide in fuel gas is a sign of
Incomplete combustion, and a waste of fuel,
e.g. C + % Or* CO + 4000 Btu
C + 02*- COz + 14000 Btu
As air is reduced most units will smoke
before they produce CO. Large power station
boilers (having greater residence time) may
be capable of producing CO before the onset of
smoke. However, their operators do not allow
this to happen for fear of explosions in the
superheater zone.
XI. NITROGEN OXIDES
The facts about NO levels in boilers are
not as well known as those on S02> SO, and CO.
NO is produced from the oxygen and nitrogen in
the combustion air. Nitrogen in the fuel is
insignificant.
Studies of full scale equipment are not
far advanced. NO production is promoted by
(1) high flame temperatures and (2) high ex-
cess air. The flame temperature effect is
probably the more important.
If controls are found to be necessary
for the future, they will probably have to be
designed into the unit. Flue gas recirculation
and two stage combustion are possible routes
toward combustion at low flame temperature.
Smaller units appear to make less NOX
per pound of fuel than larger units.
Thiiiin* appro imol^ty
100 Ibs/h, flu. ga>
wild, from .act.
0 1.0 . 2D
Boibf Oj at economize outlet
Figure 13. Effect of excess air and fuel atomizing pressure on flue gas solids burden
12
-------
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.
Fi qu re
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.
I
i
:' * **.r £!*'!*%lvV.%1 V*^'* V.
''•'•"'••'''"•'TRANSVERSE SECTION * >* • '
LONGITUDINAL SECTION
Figure 2. Single-retort underfeed stoker.
MULTIPLE-RE TORT 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
-------
Coal Burning Equip me nt
COAL HOPPER
COAL RAMS
ASH-
DISCHARGE PLATE
FUEL
DISTRIBUTORS
3. Multiple-retort underfeed stoker.
COAL HOPPER
C04L GATE
SPROCKET
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 stearr. 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 -t. B 4 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.
V VIBRATING-GRATE STOKER
This unit consists of a water-cooled grate
structure on which the coal moves fro... me
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'
C04L HOPPER.
COAL GAT
OVERFIRE-AIR NOZZLES
Figure -5. Vi brat i nq-qrate stoker furnace.
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.
-------
Coal Burning Equipment
FLUE GAS
EXHAUST
-STEAM
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
1
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 stronglyinfluenced by high
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
Ai r heater
Figure -8. Pul verijed-coal-fired
uni t.
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.
-------
Coal Burning Equipment
Pulverized-fuel-fired boilers range in capacity
from 200, 000 to several million pounds of
steam per hour.
U) HORIZON TIL Fl MINI,
SECOND!«V *l R-. \ \
CVCLOHE -
(0) CYCLONE FIRING
It) OPPOSfB-IHCLIIieo UPm
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.
SCREENEO-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.
-------
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 (length3) 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
+ | 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 as 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
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.
C 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.
D 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
-------
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
-------
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
-------
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 d 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.
-------
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 stearn
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
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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
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.
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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: (l) 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, econcrr,/ 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 COAL HANDLING SYSTEM (Storage
Area to Furnace)
A Coal Thawing
The first phase of coal handling at the plant,
at least during extremely cold weather is
the thawing of the coal so that it may be un-
loaded. This is accomplished in many ways;
1 Steam may be introduced into the
pockets of the hopper coal cars by
means of a nozzle, at the partially
opened car doors. This is effective
but it does add moisture to the coal
which may cause added freezing prob-
lems if the coal is unloaded into an un-
protected bunker or silo where freezing
may reoccur.
2 Coal cars may be heated with a "flame
thrower" type of oil burner.
3 Coal cars may be placed over oil, gas
or coal fired thawing pits.
4 Coal cars may be heated by infra-red
electric heaters.
When possible it is wise to have items
1, 3, and 4 performed in a closed or
protected shed or covering.
Some American manufacturers of this
equipment are:
a Aitken Products Company (Infra-red)
b Fostoria Corporation
c J. C. Corrigan Company
Incorporation
d Hanck Manufacturing Company
B Unloading Point
The coal may be unloaded readily from
an overhead trestle or over a track
hopper. It is well to have a grill work
covering over the hopper or over the
opening under the trestle. This steel
grill work covering should have openings
5" X 5", 6" X 6" or 7" X 7", preferably.
If the openings are smaller, they tend to
clog and slow the discharge of coal from
the car. If the openings are larger they
tend to become less safe for the work-
men and they fail to catch or hold back
foreign materials that should be kept
from the coal being handled into the
plant.
C Unloading Devices
Coal cars may be unloaded by (1) over-
head clam shell buckets (2) car shakers
or (3) car turnovers.
The first has limited application. The
third is suited primarily for consumers
of large tonnage (50 or more cars per
day). The second type of unloader is of
importance primarily to the industrial
and utility plants using two to fifty cars
per day.
Some American manufacturers of this
equipment are:
1 Allis Chalmers Manufacturing Company
2 American Engineering Company
3 Hewitt-Robins Incorporation
4 Heyl and Patterson, Incorporation
5 Industrial Brownhoist Company
6 Link Belt Company
7 National Conveyor and Supply Company
8 Silent Hoist and Crane Company
Incorporation
9 Stephens-Adamson Manufacturing
Company
10 Webster Manufacturing Company
11 McDowell-Wellman Engineering
Company
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Coal Burning - Design Parameters
D Feeder
Normally the coal flows from the track
hopper on to a short conveyor called a
feeder. There are several types of
feeders including: (1) Belt; (2) Apron;
(3) Screw; (4) Flight, and
(5) Reciprocating.
Manufacturers of this equipment will be
shown under conveyors.
E Magnetic Separation
It is well to have some sort of magnetic
device at or near the discharge end of the
feeder to remove any tramp iron or steel
material that might become a potential
hazard to further intra plant handling.
These devices may be magnetic pulleys
over which the coal passes or electro-
magnets suspended above the coal flow
on the feeder.
Some American manufacturers of this
equipment are:
1 Bauer Brothers Company
2 Cutler-Hammer, Incorporation
3 Dings Magnetic Separator Company
4 Eriez Manufacturing Company
5 Homer Manufacturing Company
6 Patterson Foundry and Machine
Company
7 Robinson Manufacturing Company
8 Stearns Magnetic Manufacturing
Company
F Crushers
If the plant uses two or more cars of coal
per day it might well have a crusher for
use when emergency conditions requires
the purchase of coal of a larger top size
than is technically proper and suitable for
the burning equipment. Such equipment
might well be placed at the discharge
point of the feeder.
Some manufacturers of this equipment
are:
1 Allis Chalmers Manufacturing Company
2 American Pulverizer and Crusher
Company
3 C. O. Bartlett and Snow Company
4 Bauer Brothers Company
5 Gruendler Crusher and Pulverizer
Company
6 T. J. Gundlach Machine Company
7 Hardinge Company Incorporation
8 Jeffrey Manufacturing Company
9 Link Belt Company
10 McNally Pittsburgh Manufacturing
Corporation
11 Pennsylvania Crusher, Div of Bath
Iron Works
12 Smith Engineering Company
13 Sprout, Waldron and Company
14 Traylor Engineering and Manufacturing
Company
G Automatic Samples
The large users of coal (industrial,
institutional and utility) should be con-
cerned with the quality of the coal shipped
to them. Periodic and regular samples
should be taken. These samples must
be representative of the coal received
or they are worse than no sample at all.
All samples should be so constructed
such that in use the sampling device cuts
the full stream of coal. Samplers are
well located after the crusher.
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Coal Burning - Design Parameters
Some American manufacturers of this
equipment are:
1 Denver Equipment Company
2 Fuller Company
3 Galigher Company
4 Hardinge Company Incorporation
5 Heyle and Patterson, Incorporation
6 Stephens-Adamson Manufacturing
Company
H Elevators
If the coal is to be elevated to an overhead
bunker, bin or a silo, elevating equipment
such as the following may be used:
1 Bucket Elevator
a Swinging bucket
b Centrifugal discharge
c Continuous discharge
d Gravity discharge
2 Bulk Flow
3 Skip Hoist
4 Pneumatic
Some American manufacturers of this
equipment are:
1 Barber Greene Company
2 C. O. Bartlett and Snow Company
3 Beaumont Birch Company
4 Fairfield Engineering Company
5 A.B. Farquhar Company
6 Gifford-Wood Company
7 Joy Manufacturing Company
8 Sauerman Brothers, Incorporation
9 Link Belt Company
10 La Del Conveyor and Manufacturing
Company
11 Many large rubber companies
I Conveyors
Lateral movement may be necessary
either before or after the elevators.
. This movement may be done by the
following conveyors:
1 Belt
2 Flight (scraper, drag)
3 Apron
4 Screw
5 Bulk flow
Some American manufacturers of this
equipment are:
1 Allis Chalmers Manufacturing
Company
2 American Hoist and Derrick Company
3 John Austin, Inc.
4 Beaumont-Birch Company
5 Blaw-Knox Company
6 Bucyrus Erie Company
7 Gifford-Wood Company
8 Heyle-Patter son, Inc.
9 Frank Hough Company
10 Link-Belt Company
11 Oliver Corporation
11
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Coal Burning - Design Parameters
12 Sauerman Brothers Inc.
13 Wellman Engineering Company
14 Goodyear Tire and Rubber Company
15 B. F. Goodrich Company
16 U.S. Rubber Company
17 International Harvester Company
18 J.I. Case Company
19 Caterpillar Tractor Company
20 Le Tourneau-Westinghouse Company
J Scales
An accurate determination of power plant
operations requires some reasonable
knowledge of the amount of coal used over
a given period of time. A number of
methods are used:
1 Car weights and stock inventory
2 Stroke counters on various using
equipment. This gives bulk or volume
flow from which the weight can be
calculated.
3 Bulk flow devices within spouts
4 Overhead weigh lorries
5 Automatic, belt flow
6 Automatic, mass trip
7 Platform scales. Where relatively
small tonnage of coal are consumed
the coal may be weighed in wheeled
vehicles or track carriers enroute
between the point of storage and the
point of use.
Some manufacturers of this equipment
are:
1 Yale and Towne Manufacturing
Company
2 Toledo Scale Company
3 Syntron Company
4 Howe Scale Company
5 Stock Equipment Company
6 Richardson Scfle Company
7 Merrick Scale Manufacturing
Company
8 Fairbanks, Morse and Company
9 Buffalo Scale Company Inc.
10 Jeffrey Manufacturing Company
K 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:
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
12
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Coal Burning - Design Parameters
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
(15) American Air Filter Corporation
L 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 finely
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
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Coal"Surning - Design Parameters
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.
M 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 (SO3), 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:
1 The concentration of the SOg present
per unit volume of the flue gas.
15
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Coal Burning - Design Parameters
( 2) The concentration of water vapor
(H^O) 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 SO3 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 SO3 to
SC>2 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 SO3 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.
N Materials of Construction
Furnace construction from the standpoint
of furnace walls may be classified as:
1 All refractory
2 All refractory - air cooled
3 Refractory - Part water wall
4 All water wall with refractory facing
5 All water walls with insulated plate
metal facing
At any earlier period in power plant
usage, refractory in the form of walls,
arches, bridge walls, baffles, etc., con-
tained and reflected the heat in order to
create very hot zones and areas. The
products of combustion were so directed
that the flow of gases was parallel to or
perpendicular to the direction of the heat
absorbing surfaces. A scrubbing action
with some turbulence of the gases at
the transfer surfaces was sought to lessen
film heat resistance and to hasten the
heat transfer. Under such conditions
most of the heat was by conduction and
convection with a relatively small amount
by direct radiation. Largely, since
World War II, the trend of design is to
accomplish a maximum of heat transfer
directly by radiant energy with a reduced
amount by conduction and convection.
With the furnace water walls (boiler and
superheater tubes) absorbing the heat
directly as cold heat with a minimum of
flue gas travel and scouring action, econo-
mizers and air preheaters must be ex-
panded in heating surface. Many
pulverized coal fired furnaces are of such
volume that the indicated heat release at
the design unit rating may be only 12, 000
to 20, 000 BTU per cubic foot per hour
with about 17, 000 BTU per cubic foot
- per hour approaching an average.
Spreader stoker fired units, generally,
average about 10, 000 BTU per cubic foot
per hour more than pulverizer units or
16
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Coal Burning - Design
average about 27, 000 BTU per cubic foot
per hour at rated operation. The great
decrease in the use of the overfeed link
grate traveling stokers and of the under-
feed stokers makes their data less
common. At an earlier time, however,
it was considered that the heat release of
these latter two types of equipment with
relatively smaller furnaces and all re-
fractory construction might show heat
releases of 35, 000 to 40, 000 BTU per
cubic foot per hour. In the cyclone units,
where the heat release approximates a
half to three quarters of a million BTU
per cubic foot per hour, it is apparent
that a great part of the heat recovery
must take place in the primary furnace.
Therefore, the materials of construction
are dependent upon the design of the unit
and the usage of the heat. Some furnaces
may require a refractory capable of with-
standing a very high temperature through-
out the whole unit while others may
require only a relatively small amount at
about the grate level. The use of water
wall recovery surfaces not only adds to
the unit efficiency and output but may be
a means of lessening furnace maintenance
for industrial power plant usage.
The following figures have been noted as
being somewhat typical of the heat transfer
in BTU per square foot of heat absorbing
surface per hour:
Water walls
Superheater
Boiler
Economizer
Air Preheater
50,000 to 140,000
7, 500 to 15,000
2,000 to 6,000
3, 000 to 4, 500
500 to 800
From the standpoint of the stokers alone
the firing rate in BTU per square foot of
grate surface per hour approximates as
a maximum:
Single retort underfeed stokers -
450, 000 to 500,000
Multiple retort underfeed stokers -
500,000 to 675,000
Traveling grate overfeed stokers -
425,000 to 550,000
The lower figure might be taken as one
where the stoker maintenance with
proper care and attention might not be
excessive. But the higher figure likely
would be cause for increased maintenance
costs.
It has been shown that the materials of
construction combined with the unit de-
sign does have a bearing upon the costs
of operation. Moreover, it is generally
agreed that the current stage of the
metallurgy of boiler construction is the
determining factor as to what can be done
in this respect.
O Instruments and Controls Requirements
As load conditions become more variable
and the power plant units become more
complex, the necessity for a constant
readiness to meet those conditions by
fuel feed, air adjustments, control of
temperatures, control of various drafts
and pressures becomes more demanding.
Man power can be used to make such
changes. But man power can become
tired and lax in attention and performance.
The modern unit cannot tolerate any lack
of instant change to meet the operating
conditions and needs. A proper instru-
mentation of gages, meters and controls
to meet the status of performance sought
should be considered and used. In effect,
then, the instruments take over the de-
tails of firing and the operator becomes
a type of supervisor. But the instruments
cannot think and the operator must be
well enough acquainted with their use and
meaning along with the fundamentals of
good combustion to know when conditions
within the unit are proper and satisfactory.
Instrumentation must be adequate but
should not be carried to an extreme be-
yond the needs. Otherwise much data
17
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Coal Burning - Design Parameters
may be collected that for all practical
purposes is rather worthless except
possibly of some academic interest.
Then, briefly, one should consider to
each unit its own instrumentation
according to the needs.
Meters, gages and controls to show the
steam load, steam pressure, water
level, coal feed, air adjustments, drafts
and dampers for same, and temperatures
where needed are primary. Management
and operators must determine what
instrumentation is necessary, what
instrumentation might be desirable but
not completely necessary and what instru-
mentation is a luxury.
In some cases, electric eye equipment
may be installed and adjusted so as to
warn of an operating condition approaching
nuisance proportions. Properly used
this equipment may become a means of
bringing about an improved firing techni-
que. In some cases, a simple arrange-
ment of mirrors can be, if properly
observed, a means of helping an operator
to correct faulty firing and lessen a
potential nuisance. A fireman can
accomplish a great deal in improving the
efficiency of his unit and in lessening
operating faults by periodically observing
his firing conditions and correcting when
and where necessary. In many cases the
unit and facility already has ample re-
quirements for good results but there is
a laxness on the part of the operators to
make use of that which is available.
Some American Manufacturers of
instrument and control equipment are:
(1) Allen-Bradley Company
(2)Askania Regulator Company
(3) Bailey Meter Company
(4) Brooke Engineering Company, Inc.
(5) General Electric Company
(6) Hagan Corporation
(7) Hays Corporation
(8) Republic Flow Meter Company
(9) Leeds and Northrup Company
(10) Taylor Instrument Company
(11) Minneapolis-Honeywell Regulator
Company
(12)Hoskins Manufacturing Company
(13) Ellison Draft Gage Company
(14) Weston Electrical Instrument
Corporation
P 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.
18
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Coal Burning - Design Parameters
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.
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.
19
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COAL BURNING-GOOD OPERATION 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 refractciy construction, a higher
condition of draft (read in inches HnO) 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 H^O, 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 heat available
in the gas-es 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,
Kentucky.
PA. C.ce. 11. 5. 66
Department of Health, Commonwealth of
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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
Fly ash collectors (particulate control
equipment) are not considered as heat re-
covery equipment. They may be a means,
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
1900 to 2600°F
450 to 750°F
Leaving boiler and
entering economizer
Leaving economizer and 350 to 550°F
entering air preheater
Leaving air preheater
and entering stack
250 to 350UF
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.
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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.
Ill 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 inade 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
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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.
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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-
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 carhnn 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.
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Coal Burning - Good Operational Practices
VIII Operating at Other Than the Manufacturer's
Specifications and Design Rating
The results are dependent upon the extent of
the variation from the specifications or
rating. If done within reason both as to
amount of change from the optimum and to
the duration no serious difficulties should
arise. In some cases even a great amount
of good might be done from the technical
knowledge that might be gained. Normally,
the efficiency of the unit decreases both
above and below the design or optimum rating.
However, the results of the change from the
optimum can only be learned by trial even
though the results might be anticipated.
At an early time, prior to the 1920's the
output of the boilers were indicated by a
"Manufacturer's Rating. " As improvements
in furnaces, firing equipment, combustion
controls and firing technique were developed
and improved it was found that in many cases,
especially with the Stirling bent tube type
boilers the best performance was obtained
at 180 to 225 percent of the Manufacturer's
Rating. In some cases, this figure dropped
to about 140 percent of rating. In other
cases, the output reached 325 percent for
short periods of time. Many of the
standard HRT boilers seemed to give best
operations at about 140 percent of the
Manufacturer's Rating, but under some
circumstances, 180 to 200 percent of rating
could be reached.
Generally, variations from the specifications
for stoker equipment is more a function of
the quality of the coal and of its consist
(physical make up by sizes) to meet the
operating conditions. A relatively poor coal
of proper consist and preparation to fit the
needs of the equipment and conditions of use
may out perform an inherently better coal
but of normal preparation.
In summary, I believe that a reasonably
educated trial is worthwhile.
Some of the leading American boiler
manufacturers are:
A Babcock and Wilcox Company
B Bigelow Company
C William Bros. Boiler & Manufacturing
Company
D Brownell Company
E Combustion Engineering Company
F Edge Moor Iron Works, Inc.
G Erie City Iron Works
H Foster Wheeler Corporation
I Riley Stoker Corporation
J Union Iron Works
K Henry Vogt Machine Company, Inc.
L Wickes Boiler Company
M E. Keeler Company
N Kewanee Boiler Company
IX INFLUENCE OF COAL COMPOSITION
ON OPERATING PRACTICES
Basically, all coals are made up of the same
materials. But, the combination of the
vegetable matter of their origin together with
the pressures and heat involved in their
formation caused differences in the relative
amounts of their chemical composition as
well as in their physical structures.
Briefly the classification of coals by Rank
is as follows:
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Coal Burning - Good Operational Practic
Class
1. Anthracite
Group
1. Meta Anthracite
2. Anthracite
3. Semi Anthracite
Amount of Fixed Carbon
Volatile Matter or BTU
DryF.C. 98% or more
(Dry V. M. 2% or less)
Dry F. C. 92% or more, and less
than 98% (Dry V. M. 8% or less, and
more than 2%)
Dry F. C. 86% or more, and less
than 92% (Dry V. M. 14% or less,
and more than 8%)
2. Bituminous
1. Low Volatile
Bituminous
2. Medium Volatile
Bituminous
3. High Volatile
Bituminous A
4. High Volatile
Bituminous B
5. High Volatile
Bituminous C
Dry F. C. 78% or more, and less
than 86% (Dry V. M. 22% or less,
and more than 14%)
Dry F. C. 69% or more, and less
than 78% (Dry V. M. 31% or less and
more than 22%)
Dry F. C, less than 69%
(Dry V. M. more than 31%)
Moist BTU 14, 000 or more
Moist BTU 1-3,000 or more, and
less than 14, 000
Moist BTU 11,000 or more and
less than 13, 000
3. Subbituminous
1. Subbituminous A
2. Subbituminous B
3. Subbituminous C
Moist BTU 11,000 or more, and
less than 13, 000
Moist BTU 9, 500 or more, and less
than 11, 000
Moist BTU 8, 300 or more, and less
than 9, 500
4. Lignite
1. Lignite
2. Brown Coal
Moist BTU less than 8, 300
Moist BTU less than 8, 300
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Coal Burning - Good Operational Practices
The factors of chemical composition and
physical structure each have a bearing upon
the application of coal. Naturally, some
coals are better suited for some uses. In
many cases the coal can be prepared in such a
manner that, in effect, its burning character-
istics can be altered or modified. Also, by
good engineering in the equipment, in furnace
design and in the firing technique the range
of application can be broadened. And again,
I chose to call this determination Selective
Application.
For instance the ash content, the sulfur
content, the hardness or grindability of a
coal, the fusion temperatures of the coal
either alone or together may very well decide
for or against the use of a coal for certain
applications.
Good engineering may make a coal acceptable
at one point where the same coal with poorly
engineered equipment or poor firing technique
may make it unacceptable at another.
You can burn any coal on or in any coal con-
suming unit physically capable of handling
that coal with some degree of success but
the real satisfaction and economy of use is
governed by just how well the coal burned
fits the equipment and conditions of use.
Proper coal sizing and size consist must be
considered under a policy of Selective
Application, if the full potential heat energy
is to be recovered in actual Use Value.
The use of coal solely on the basis of "Cost
per Million BTU" delivered to the plant, in
itself, is not enough. This is only one item
in good coal application. A relatively in-
ferior coal may perform much better than a
superior coal under some conditions. In
some cases, a more costly coal may well
enough prove to be more economical in use.
An improper selection of coal in any one
phase can result in:
A Increased fly ash emission
B Increased soot formation
C Increased smoke emission
D Increased slag and clinker formation
E Increased coal handling costs
F Increased ash handling costs
G Increased power costs
H Increased labor costs
I Increased maintenance costs
J Increased explosion hazards
K Increased fuel bed loss
L Increased erosion of equipment
M Increased storage loss due to windage
loss
N Increased storage loss due to spontaneous
combustion
O Increased outage of unit
P Increased housekeeping problems
Q Increased personnel problems
R Lessened efficiency
S Lessened unit output capacity
T Lessened reactive rate of coal
From the standpoint of being a good neigh-
bor, a facility on the windward side of a
community or center of activity must follow
a better firing technique than another similar
facility on the leeward side. This must be
obvious from the standpoint of air pollution
without further comment.
It is not of necessity true that all poor coals
have a high sulfur and high ash content. It
is true that high sulfur and high ash coals
are not extremely high grade. It is true
that the poorer the coal the closer to its
sources it should be used. Or, the better
the coal, the greater distance that it may be
transported with economy and satisfaction.
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Coal Burning - Good Operational Practices
Freight rates are on a tonnage or mass basis
and not on a quality basis. This is simply to
point out that while all coals have a place in
our scheme of living, there are certain
limiting conditions that determine where the
coals should be used.
The terms coking and caking have been used
rather loosely over the years. This is
unfortunate because some confusion has
resulted. Technically, coke is the solid
residue of ash and fixed carbon that remains
after the volatile products of moisture and
hydrocarbons have been driven off by distilla-
tion. In this respect all coals can be coked.
But some coals mat or cake together in the
distillation process. In effect, these coals
melt before the volatile materials have been
discharged. In the course of distillation
this mass is bound together in a honeycombed
cellular residue. On occasion, coals that
normally are classed as non-caking or free
burning may cake together in irregular
masses. Also, by Selective Application and
a control of size consists those coals that
are classed as strongly caking may be made
to behave, within some limitations, as if
they had a lesser caking quality.
X NORMAL GRATE STOKING PRACTICE
The technique used in firing must be made
to match the equipment, the conditions of
use and the coal burned. An optimum ash
content for most stokers would be about
5 to 6 percent, A smaller amount of ash
may be used with care on some units. Over-
feed stokers of the traveling grate type will
do better with coal of 7 to 8 percent ash
content. Coals with much greater amount
of ash may be used but as the amount of ash
increases over optimum amounts for the
particular usage, the stokers, in effect be-
come less of a burner and more of an ash
conveyor. Such burning as does take place
is done with somewhat more difficulty.
With these as basic qualifications or optimums,
the coal must be fired in such a manner that it
is completely burned out at the dump grates
or point of discharge from the furnace. A
combustible content in the ash of 10 to 15
percent works no great hardship upon the
unit for 10 percent of a 5 percent ash coal
represents only one-half percent on the
initial coal feed.
The firemen must regulate his coal feed to
meet the load imposed upon his equipment.
The air supply must be in accord to the coal
feed. The zoned air adjustments must give
the burning reaction within the proper area
to give most efficient heat release. This
means that the stoker action and feed must
be adjusted to give the most desirable con-
tour to the fuel bed. In other words, the
fuel bed must be adequately and completely
covered and of such depth as to produce the
contour imposed upon it by the load condi-
tions. And at all times, the fireman should
be so well acquainted with his fuel bed as to
know the presence or absence of clinkers
that might become a source of trouble.
XI INFLUENCE OF HIGH SULFUR COALS
ON OPERATING PRACTICES
High sulfur coal is characterized by the fact
that all forms of the sulfur are relatively
high and not just the pyritic form alone.
Normally, most of the sulfur, even after
washing (mechanical cleaning), will be of
the pyritic (iron disulfide) form. Very often
with high sulfur coal, the pyritic form will
be as much or more than the organic and
sulfate forms combined. Since the iron is
largely in the ferrous form a low melting
point can be expected. Part of the combus-
tion process takes place in a reducing
atmosphere. This in turn tends to emphasize
the lowered melting point.
When using equipment that is already in
existence and with the load established, the
use of a high sulfur coal very likely will
require the use of a greater amount of excess
air than would be normal otherwise. This
lowers the unit efficiency. All handling costs,
all labor costs, all operating costs and all
maintenance costs, most likely, will be
increased if coal of this grade is used for any
extended period.
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Coal Burning - Good Operational Practices
If, however, the units are or have been
designed for such coal, a more satisfactory
outcome can be achieved. These units,
generally are built in such a way that the
furnaces are larger, and at the design rating,
the furnace heat release is lower. Conse-
quently, the furnaces are cooler. The spacing
between the boiler and superheater tubes
encountering the flue gases is increased so
that slag formation is lessened. If the
capacity of the units is of such size as to
merit the consideration, cyclone type units
may be installed. Then, a fuller realization
of the coal with a high sulfur content may be
gained than would be true with some other
equipment.
XII PERSONNEL
The operation of a boiler plant is a function
of four items:
A Equipment
B Fuel (Coal, in this discussion)
C Conditions
P People
Briefly the people are divided into two
classes: 1) Management; and '2) Operators.
With a proper relationship between the two,
much can be accomplished. Obviously, the
function of management is to direct. By
their leadership they can create a discipline
and a morale whereby a great good can be
accomplished by all concerned. The
training of the operators so that they can do
their job properly, efficiently, safely and
with a spirit of happiness is one phase of
their direction. The housekeeping that is
evident in a boiler room is a reflection of
the training of the operators and of the pride
in their work.
First, there must be a proper communication
between management and the operators with
the necessary freedom of communication to
both levels from both levels. In other words
communication must be a two-way approach.
For instance, it is not expected that the fire-
men and the purchasing agent be equally
acquainted with each others problems but
with a reasonable interchange of ideas as to
their particular problems under given condi-
tions much can be done to lessen each others
problems.
The firemen must have some knowledge of
a proper firing technique for handling his
specific equipment to meet the operating
needs. He must be aware of the fact that
combustion is first of all a chemical reaction
and as such the fuel and air have a definite
relationship to each other. They must be
taught to read their fires with some know-
ledge of their correctness and to relate this
knowledge to the various meters, gages,
controls and other instruments.
They must be made conscious that under
certain conditions they may be creating a
nuisance. They must be taught to observe
the amount of that nuisance and how to
lessen or within reasonable limits to over-
come and eliminate it. It is my personal
belief that any facility or person capable
of creating a nuisance is capable of
correcting it either desirably by choice or
less desirably by force. In many cases,
ample facilities either physical or mental
are already available and it is simply a
question of using that which is at hand.
10
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UNDERFEED STOKERS
Harold E. Johnson*
I SINGLE RETORT STOKERS
The single retort underfeed stoker has been
popular since the early 1920's and still has
a very definite place in a size range of between
3, 000 and 25, 000 pounds of steam per hour.
Most single retort stokers, except those for
household heating, are ram-fed, and operate
with periodic charges of coal from the hopper
to the retort. The retort runs the full length
of the stoker, and the auxiliary pushers lo-
cated at the bottom of the retort distribute
the coal from front to rear of the stoker,
while at the same time causing the coal to rise
in the retort and then spread from side to side
over the entire grate surface.
As the rising fuel approaches the incandescent
fuel bed, heat distills volatile gases which
are mixed with air and consumed in the in-
candescent zone without smoke.
The grate surface is made up of either fixed
or undulating moving grates resting atop the
retort sides and the plenum chamber enclosure,
through which the combustion air flows into the
fuel bed. The fuel bed burns and is reduced
to ash as it moves toward the dump grates
located adjacent to each sidewall of the
furnace. The ash is dumped at intervals
dictated by the ash content of the fuel.
It is, as a rule, advisable to use some of the
better grades of coal to get optimum results
with this type of stoker. -However, this
picture has been changing somewhat over the
years, and poorer grade coals can be burned
with good results, due mainly to the sizing
and cleaning processes now commonly used
at the mines.
The coal to be used should determine the size
of the stoker or grate area. Burning rates of
30 pounds per sq. ft. per hour are reasonable
when burning better grades of bituminous
coal, with ash fusion temperature above
2400°F. The burning rates should be re-
duced somewhat when burning coal with ash
fusion temperature below 2400°F.
The burning characteristics of the coal are
an important factor to be considered when
selecting stoker equipment. It is necessary
to maintain a compact fuel bed of uniform
porosity if optimum operation is to be ob-
tained. Free burning coals, those with a
free swelling index of 6, and below, are
best suited to the single retort stoker with
fixed grates, as the high coking coals, those
with free swelling index above 6, tend to
swell, causing the flue bed to arch and rise
off the grate. For this reason the high
coking coal should be burned on single re-
tort stokers equipped with undulating mov-
ing grates. The undulating, or wave like
grate motion, breaks up arch formation
and keeps the fuel bed porous without manual
poking.
If high operating efficiency is to be realized
it is necessary to maintain correct coal-air
ratio. Since it is difficult to manually
maintain the correct fuel and air supply at
varying loads, it is advisable to employ an
automatic combustion control system. The
modern single retort stoker is equipped with
an adjustable coal feed device which, together
with the control damper of the combustion
air fan, can be connected to the combustion
control system, maintaining automatic
synchronization of fuel and air supply over
the entire load range.
II MULTIPLE RETORT STOKERS
The multiple retort stoker, although not as
popular today as some of the other firing
methods, is still preferred by many plants.
This stoker is offered in sizes to generate
from approximately 20, 000 to 500, 000 pounds
of steam per hour. The grate surface is
made up of a series of retorts separated by
* Cincinnati District Manager, Detroit Stoker Company. Presented at the Industrial Coal Con-
ference, University of Kentucky, Lexington, Kentucky. April 1965.
PA.C.ce.28.9.66 1
-------
Underfeed Stokers
Figure 1. Sectional View of Single Retort Stoker with Fixed Grates
Figure 2. Sectional View of Single Retort Stoker with Undulating Moving Grates
BACKWARD
Figure 3. Sectional View Showing Grate Movement of the Undulating Grate Stoker
-------
Underfeed Stokers
rows of air tuyeres. Feed rams move coal
from the hopper to each retort, secondary
pushers then distribute the coal along the
length of the stoker. The combustion air
flows through the air tuyeres located between
each retort to the fuel bed, promoting active
burning of the distilled volatile gases and the
fuel mass as the coal is moved slowly rear-
ward to the ash discharge section.
Since the same coal burning principles apply
to single and multiple retort stokers, the same
design criteria apply to both stoker types.
Ill CONCLUSION
An attempt has been made in the foregoing
discussion to outline the design criteria of
underfeed stokers, as well as its advantages
and disadvantages. The underfeed stoker has
for many years played an important role in
power and heating, continued usage of these
stoker types for many applications in the
future is foreseen.
'•*T;.: • .
Figure 4. Sectional View of Multiple Retort Stoker - Available in Sizes to
500, 000 Pounds of Steam Per Hour
-------
SPREADER STOKERS
John L. Dick*
I INTRODUCTION
In the past twenty-five years spreader stokers
have played a prominent role in the production
of steam, in the capacity ranges up to 400, 000
pounds of steam per hour, both in this country
and abroad.
The wide acceptance of spreader stokers can
be attributed to the design flexibility and
ability to burn a wide range of fuels success-
fully with low maintenance, high daily effi-
ciency, and simplicity of operation.
Fuels considered not suitable for use on other
stoker types can now be burned on spreader
stokers with complete assurance of obtaining
satisfactory results with a minimum of effort
and expense.
It may be beneficial at this time to describe
briefly the design principles of spreader
stoker operation for a more complete under-
standing of this method of firing.
II PRINCIPLE OF SPREADER STOKER
OPERATION
Basically, the operation consists of metering
fuel to the furnace by means of feeders and
distributors mounted on the stoker front,
over the grate, employing revolving rotors
with specially designed blades to insure uni-
form distribution, both laterally and longi-
tudinally. The fine particles burn in suspension
while the coarse coal burns on a protective
layer of ash on the grate.
Air is admitted to the fuel bed through a
series of closely spaced, venturi shaped, air
ports cast in the grate to provide uniform
air flow to the entire active grate area.
The fuel introduced into the furnace ignites
rapidly, starting to release hydrocarbons the
instant the fuel enters the high temperature
zone, making it possible to burn both highly
coking and low ash fusion coals without
special preparation.
Ill COAL FEEDERS
The number, location, and spacing of coal
feeders are important factors to be con-
sidered in the initial design. The total feed-
ing area, determined by the length of the
rotor blades, should never be permitted to
go below 40% of the grate width, otherwise,
operation may suffer from mal-distribution.
The feeder spacing should be kept to a mini-
mum to avoid "fishtails" (areas receiving no
fuel). Feeders are manufactured in different
widths to permit proper spacing and the most
desirable relationship between feeder and
grate width.
The feeders are directly connected to the
combustion control system and the fuel feed-
ing rate responds instantaneously to rapid
load changes.
The fuel discharges from the coal hoppers to
the rotor blades which are specially designed
to insure proper distribution on the grate.
IV TYPES OF SPREADER STOKERS
There are various types of spreader stokers,
however, the main difference is in the grate
design and operation.
The intermittently cleaned grate type stokers
(Figure 1) have either stationary or dumping
type grates that are periodically cleaned when
the ash accumulation reaches a depth of six
to eight inches. The dumping frequency is
wholly dependent upon the burning rate and
percent of ash in the fuel. These models
are constructed in individual sections to pro-
vide shutoff of the feeder blast gate and
plenum chamber on the particular section
*Special Sales Engineer, Detroit Stoker Company. Presented at the Industrial Coal Conference,
University of Kentucky, Lexington, Kentucky. April, 1965.
PA.C.ce.29. 9.66 ,
-------
Spreader Stokers
Figure 1
of the grate to be cleaned, while the remain-
ing grate section or sections remain in
operation.
There are, for all practical purposes, three
types of continuous cleaning grate stokers,
namely, Continuously Reciprocating, Inter-
mittently Vibrating, and Traveling Grate.
The reciprocating grate (Figure 2) consists
of alternate rows of continuously reciprocating
grates imparting forward movement of the
ash for automatic discharge at the front.
The vibrating grate stoker employs a vibration
generator mounted on the grate frame that is
periodically energized to move the ash to the
discharge end by means of intermittent
vibration.
The front continuous ash discharge traveling
grate stoker (Figure 3) is very popular in
capacities up to 400, 000 pounds of steam per
hour. This type consists of an endless chain
of grates slowly moving through the furnace
permitting the ash to reach a depth of 3 or 4
inches before being automatically discharged
into the ash pit.
The grate types described above can be
placed in two categories, namely; Agitating
and non-agitating. The agitating types are
the reciprocating and vibrating. The non-
agitating are the stationary, intermittent
dumping, and the continuously traveling
grate.
It is generally recognized that lower ash
fusion coals can be burned more successfully
on non-agitating grates than can be burned on
grates employing agitation.
V THE ADVANTAGES ASSOCIATED WITH
SPREADER STOKER OPERATION
A Ease of Operation
The design of the spreader stoker permits
adaptation to automatic combustion control
systems, permitting synchronization of the
fuel-air ratio over the complete load range
-------
Spreader Stokers
Figure 2
and providing high efficiency while, at the
same time, requiring little attention on the
part of the operator.
B Low Maintenance
Records indicate that maintenance cost on
spreader stokers is exceptionally low.
C Greater Fuel Flexibility
Spreader stokers successfully burn a very
wide range of fuels, from the high grade
eastern bituminous to the poorer fjrade
sub-bituminous and lignites in the West.
In addition, many waste and cellulose
fuels, such as, hogged and unhogged bark,
wood chips, sawdust, shavings, bagasse,
and others, burn separately or in com-
bination with coal.
Spreader stokers proved their flexibility
during and following World War II, when
it became necessary to burn all types of
available fuels with widely varying
analyses brought on by fuel rationing.
Excellent performance was obtained on
spreader stokers during this era and is
one of the most popular types of fuel
burning equipment in use today.
D Availability
Spreader stokers have a very high avail-
ability factor. Surveys and service records
indicate many plants operating 24 hours per
day, seven days per week, have one scheduled
outage per year during the annual inspection
pe riod.
Figure 3
-------
Spreader Stokers
At Central Soya Company, Decatur,
Indiana plant, an 80, 000 pound per hour
boiler served by a Detroit Roto-Grate
Stoker has operated more than 13 years,
consuming over 475, 000 tons of Indiana
coal on the original set of grates without
a single forced outage. This plant operates
around the clock, 355 days per year, al-
lowing 10 days each year for annual in-
spection and rehabilitation.
Spreader stokers are designed so that
maintenance can be performed without
having to take the unit out of service.
E Rapid Response to Changing Loads
The fuel input to the furnace is always in
direct proportion to the steam demand, and
immediately upon sensing a change in load,
the combustion control system repositions
the fuel feed and air flow rates to satisfy
the changing conditions instantaneously.
The partial suspension burning responds
readily to changing conditions, and severe
load swings can be handled without suffering
loss of steam pressure, and without over
shooting.
F High Daily Efficiency
The control of the fuel-air ratio over the
entire operating range results in high
operating efficiency.
Effective control of the combustion air
through the grates and positive air seals
between the stoker and boiler proper make
it possible to operate with low excess air
over the load range, resulting in high
operating efficiency.
It is recognized that more complete com-
bustion is obtained with spreader stoker
operation than with other stoker types,
resulting in high efficiency.
G Low Initial Cost
The ability of spreader stokers to operate
at high burning rates results in the use of
more economical boiler shapes.
H Combination Firing of Auxiliary Fuels
The application of spreader stokers to boilers
designed with gas and oil firing is quite numer-
ous. The only limitation or restriction is in
the location of the burners. Sufficient spac-
ing between the top of the grate and nozzles
should be maintained to avoid direct flame
impingement on the grate surface. Changing
from one fuel to another can normally be
accomplished in a 15to20 minute interval.
I Safety in Operation
In the many years we have been producing
and installing spreader stokers, we have
neve.r recorded a single case of gas ex-
plosion attributed to the stoker as a result
of partial suspension burning.
Fires under the grate are practically non-
existent because the siftings in the sifting
hopper contain a very small percentage of
unburned carbon.
VI THE DISADVANTAGES ASSOCIATED
WITH STOKER FIRING
A Fly-Carbon
Whenever fuel is burned in suspension or
when forced draft air is employed to
accelerate the burning process, particles
of ash and unburned carbon are picked up
in the flue gas leaving the furnace. These
particles are commonly referred to as
fly-ash or fly-carbon.
In spreader stokers, burning fine particles
of fuel in suspension, the quantity of carry-
over is sufficient to warrant collection and
returning of these particles to the furnace
for burning.
To give you a comprehensive report on
fly-carbon reinjection we refer you to a
paper recently presented at the 1964 In-
dustrial Coal Conference held at Purdue
University, entitled, "Trends in Fly-
Carbon Reinjection, (Developments and
Improvements)", by Mr. Harold L. Knox,
-------
Spreader Stokers
Assistant Chief Engineer, Detroit Stoker
Company, Monroe, Michigan.
B Low Load Operation
The ability of spreader stokers to handle
light loads depends on many factors. One
of these is the burning rate per square
foot of grate per hour. On stationary and
intermittent dumping grate types the
burning rate is usually established between
350, 000 and 550, 000 BTU per square foot
per hour, depending upon the ash content
of the fuel and the number of feeders
employed.
On continuous cleaning grate stokers no
provisions have to be made for interruptable
cleaning periods and much higher burning
rates are used ranging between 550, 000 and
750, 000 BTU per square foot per hour.
These figures represent safe, smokeless
operation anywhere from 3 to 1 to a 6 to 1
load range, depending on the burning rate
at the maximum continuous rating and the
stoker type.
During very light load operation the furnace
temperatures are too low to sustain com-
plete combustion because of the low burning
rates. At these very low loads it is some-
times more advisable to utilize steam jets
through the furnace sidewalls rather than
overfire air jets to create furnace
turbulence.
The distribution of fuel on the grate is an
important factor in smoke elimination at
reduced ratings. If the fuel bed thickness
is not uniform the low pressure air passing
through the fuel bed will escape through
the shallow sections leaving the thicker
sections starved of air.
The proper number and spacing of the
cinder return lines can also have a bear-
ing on smokeless operation. If the return
lines are not designed properly to evenly
spread the returned material, excess
loading of fly-ash could produce ridges on
the fuel bed, resulting in a smudge pot
effect.
VII CONCLUSION
In the foregoing article we have endeavored
to present the design features of spreader
stoker firing along with its advantages and
disadvantages.
There are a great many spreader stoker
installations throughout the world represent-
ing a substantial portion of the coal burned
annually, the continued popularity of this
type of firing method is foreseen.
-------
ANOTHER LOOK AT THE TRAVELING GRATE STOKER
Herbert I. Hollander, P. E. *
In light of the greater sensitivity and increas-
ing emphasis being placed on atmospheric
contamination, air pollution control engineers
and officials are scrutinizing more closely
and re-evaluating the performance criteria
established for not only coal fired installations
but for all gas emitting devices.
This has prompted the reassessment and re-
newed interest in the "old reliable" mass
burning, gate fed type, travelling grate
stoker. When properly designed and applied,
this stoker type can be operated to provide
wide load range performance without object-
ionable smoke or particulate discharge from
the stack.
The two basic types of mass burning, gate
fed, traveling grate stokers are the 'bar and
key" grate and the "chain" grate. As the
nomenclature implies, the "bar and key"
grate surface is made up of relatively narrow
keys or clips mounted on bars or racks, which
are pulled or pushed by chain assemblies
through the furnace. In general the clips
of the chain grate stoker form the chain as
well as the grate surface.
Both stoker types draw coal from the stoker
hopper with the fuel bed depth controlled by
a vertically adjustable gate across the width
of the unit. The fuel bed is carried over the
several air zones of the stoker for stage
burning. The ash is ultimately, discharged
into the ash hopper at the rear. Figure 1.
FIGURE 1 TYPICAL RILEY TRAVELING GRATE STOKER
*Riley Stoker Corporation. Presented at the Industrial Coal Conference, University of Kentucky
Lexington, Kentucky. April 1965.
PA.C.ce. 30.9.66
-------
Another Look at the Traveling Grate Stoker
The entire coal feeding and burning action
occurs without any agitation of the fuel bed
thereby minimizing dust entrainment in the
rising gases.
Anthracite, lignite as well as bituminous
coals can be burned. Of the bituminous
types, the free burning coals are preferred.
Coking coals having relatively high free
swelling indices can be burned successfully
provided the coal sizing is accurately con-
trolled, i.e., 1 - 1/2"X 3/8" with uniform
size gradation. The recommended coal sizing
for free burning friable coals is 1 - 1/4" X
0" and for non friable coal 3/4" X 0" with not
more than 50% passing through 1/4" round
mesh screening. Finer size free burning
coals, even mine screenings of minus 3/8"
can be burned but with some penalty in higher
carbon loss, Figure 2. Coals having as much
as 30% ash have been, and are being, burned
with complete satisfaction on units especially
designed for this duty.
DISTRIBUTION Of SIZES OF COAL
which will increase the moisture in the fuel
up to approximately 10%, should be performed
as uniformly as possible.
As with all stoker types these machines are
also quite sensitive to segregation or poor
distribution of coal sizes and moisture con-
tent. Unless the fuel consist if uniform across
the width of the grate the fuel bed may not
burn uniformly and may result in a "tail, "
and some unburned carbon may end up in the
ash hopper.
Stoker and furnace configuration is of prime
importance in the performance of any unit.
Unless the furnace configuration includes a
rear arch, the mass burning traveling grate
stoker type will have a thin fire in the burn-
out zone and therefore high excess air in
this area. This can usually be avoided by
using a properly designed rear arch similar
to that shown in Figure 3 to divert the excess
air expeditiously into the rich zone of burning
volatiles thereby increasing the CCL at the
furnace exit.
M fill
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ARCH FURNACE
FIGURE 2
It has been found that for most coals these
stoker types require some degree of water
or steam tempering. The very fine dust in
coals are reduced when they are mine washed
before shipment, and therefore the percentage
of retained moisture from the washing oper-
ation, in the coal received at the plant,
minimizes or eliminates the need for tem-
pering at the stoker equipment. Tempering,
ASH HOPPER SIFTINGS HOPPER
FIGURE 3 ARCH FURNACE
On occasion, to reduce initial cost, some com-
promized installations are made without rear
arches, Figure 4. Mixing of the rising rich
and lean furnace gases is attempted by em-
ploying overfire air. However, this has been
found to be only partially effective and some
of these installations still suffer high excess
-------
Another Look at the Traveling Grate Stoker
OPEN FURNACE
ASH HOPPER SIFTINGS HOPPER
FIGURE 4 OPEN FURNACE
PREDICTED EXCESS AIR AT FURNACE EXIT
FOR
RILEY TRAVELING GRATE STOKERS
200 250 300 350 400 *iO 500
GRATE HEAT RELEASE BTU PER SO FT PER HR « 1000
A-Arch Furncce, FIGURE 3
B-Open Furnoce or Furnoco Wilh
No Reer Arc.l, FIGURE 4
FIGURE 5
air and sometimes even smoke. Optimum
performance can be obtained only by using
both the rear arch and employing high pressure
overfire air.
Figure 5 illustrates excess air quantities at
the furnace exit with each of the furnace con-
figurations described at various grate heat
release rates.
There are several significant and sometimes
conflicting influences in selecting the optimized
stoker-furnace configuration. To minimize
dust entrainment in the gases, the stoker
grate heat release rates should be conser-
vative which will also reduce the ashpit loss.
Excessively wide stokers should be avoided
so as to reduce the problem of uniform fuel
size distribution across the width of the
grate, Figure 6.
RECOMWF.NDEO COAL FEED RATES
RILEY TRAVELING CRATE STOKERS
W 75 100 150 200
BOILER CAPACITY-pourds Jteom per hour x 1000
MAX. RATES FOP RANK INDEX AS SHOWN
Ronnie..-aTU-Zkg-
%VH t 10
FIGURE 6
-------
Another Look at the Traveling Grate Stoker
Some basic design criteria to provide a grate
and furnace design for good practical overall
performance, are illustrated in Table 1.
Table 1
BASIC DCSICN CRITERIA AT »AXI»U« CONTINUOUS RATING
Ath Softening Temperature (raducmg atmosphere) * F 190n 223pa.obo*e
Grot* Heol Releote Roll . Blu input hour Iq (l g.ott 01*
Grot* Coal Feed Rat* pound* hour foot itoliet vjldrh
Furnace Heat Liberation Blu input hour cu ft furnace «
Flame Travel . (diltonce from grolet to lutnace *
-------
CORROSION AND DEPOSITS FROM COMBUSTION GASES
William T. Reid*
A rough estimate a few years ago by the
Corrosion and Deposits Committee of ASME
placed the direct out-of-pocket costs of ex-
ternal corrosion and deposits in boiler fur-
naces at several million dollars a year. It
is difficult to pinpoint costs directly, but
certainly the unscheduled shut-down of a
large steam generator through failure of a
superheater element can be an expensive
operation. Crossley of CEGB in England
estimates that an outage of a 550-megawatt
unit for one week costs $300,000. Hence
extensive efforts have been made in this
country and abroad to learn more about the
factors that lead to metal wastage and de-
posits and how to control them in combustors
of all kinds.
Of the fuels being used for central-station
power plants, only natural gas is free from
the "impurities" that cause these problems.
Ash in coal and in fuel oil and the presence
of sulfur lead to a wide variety of difficulties.
In boilers, deposits form within the furnace,
on the superheater and reheater elements,
in the economizer, and in the air heater.
In gas turbines, combustor problems are not
so severe, but deposits on turbine blading
can be disastrous.
Although deposits may be objectionable in
themselves, as thermal insulators or flow
obstructors, usually it is the corrosion con-
ditions accompanying deposits that cause the
greatest concern. This has been particularly
true in boiler furnaces. Here, deposits
interfere with heat transfer and gas move-
ment, but these can be compensated in part
by engineering design. On the other hand,
corrosion beneath such deposits can cause
rapid metal wastage, forcing unscheduled
outages for replacement of wall tubes or
superheater elements.
With the recent trend to larger and larger
steam generators, even up to 1130 megawatts,
the importance of eliminating such outages
grows in importance. This is the reason
mainly, why so mucii attention has been
paid recently to investigating the causes of
corrosion and deposits, and to seeking
corrective measures.
IMPURITIES IN FUELS
Although natural gas, with its low sulfur
content and complete freedom from metallic
elements, is the only fuel not causing
troubles with corrosion and deposits, its
availability and cost limit its use for steam-
electric plants to geographical areas where
gas is less expensive than other fuels on a
Btu basis. Thus, despite its freedom from
corrosion and deposits, natural gas is the
source of energy for only a fifth of the
electricity generated in this country. It is
important to realize,' then, that although
corrosion and deposits are indeed trouble-
some in the operation of steam-electric
plants, it is only one of many factors that
play an important role in selecting a fuel
or designing a power plant to operate at
minimum cost.
Residual fuel, which provides the energy
for about 6 percent of our generated
electricity, usually contains all the impuri-
ties present in the original crude oil. Of
these, sodium, vanadium, and sulfur are
most troublesome. Typical limits for these
impurities/are, for sodium, 2 to 300 ppm in
residual fuel, or about 0. 1 to 30 percent
Na2O in the ash; for vanadium, 0 to about
500 ppm in residual fuel, or 0 to 40 percent
V2O5 in the ash; and for sulfur, up to 4 per-
cent in residual fuel, with a maximum of
40 percent 803 appearing in oil ash depending
upon_the method of ashing.
*Senior Fellow, Battelle Memorial Institute, Columbus,
Ohio. Presented at the Residential Course on Combustion
Technology, Pennsylvania State University, 1966.
PA.SE. 26. 12.66
-------
Corrosion and Deposits From Combustion Gases
With coal, which furnishes more than half
of the energy converted into electricity, the
impurities consist mainly of SiO2, A12O3,
Fe2O3, CaO, MgO, the alkalies, and, of
course, sulfur. The range of these ash
constituents varies widely, and they may
exist in many mineralogical forms in the
original coal. Sulfur may be present even
up to 6 percent in some commercial coals,
but the sulfur content usually is below 4
percent. Sulfur retained in coal ash as 303
ranges up to about 35 percent, depending
upon the method of ashing and the amount
of CaO and MgO in the ash. In coal-ash
slags it is seldom more than 0. 1 percent.
Chlorine is frequently blamed for corrosion
with English coals in which it occurs up to
1 percent; it seldom exceeds 0. 3 percent in
American coals, and it usually is less than
0. 1 percent. Because less than 0. 3 percent
chlorine in coal does not cause problems
through corrosion and deposits, chlorine in
American coals generally may be neglected
as a source of trouble. Phosphorus, which
occurs up to about 1 percent as P2Oc in coal
ash, was a frequent source of deposits when
coal was burned on grates. With pulverized-
coal firing, however, it is seldom held
responsible for fouling.
PROPERTIES OF COAL AND OIL ASHES
Coal Ash
Most of the earlier studies of coal ash
were aimed at clinkering problems in
fuel beds. Later, studies of ash were
concerned with the unique problems in-
volved with slag-tap pulverized-coal-
fired boiler furnaces. Ash deposits,
collecting on heat-receiving surfaces,
cause no end of trouble because they
interfere with heat transfer. In the
combustion chamber, particularly in
pulverized-coal-fired slag-tap furnaces,
the layers of slag are fluid and can cover
much of the heat-receiving surface.
In dry-bottom furnaces, wall deposits
are made up largely of sticky particles
that coalesce to cover the tubes in
irregular patterns. As the gases cool on
passing through superheaters and re-
heaters in either type of furnace, adherent
ash deposits sometimes become so ex-
tensive as to block gas flow. In air
heaters, ash accumulations again can be
troublesome.
The flow properties of coal-ash slags
were investigated extensively in this
country nearly three decades ago when
slag-tap furnaces were still quite new.
More recently, those early data have been
rechecked and affirmed in England. Al-
though coal ash makes up a 6-component
system, it has been found possible to
combine compositional variables so as to
provide a relatively simple relationship
between viscosity, temperature, and
composition. It has been found, for
example, that slag viscosity above the
liquidus temperature can be related
uniquely to the "silica percentage" of
the slag, where
Silica percentage =
Si02
SiO
2 + Fe2O3 + CaO + MgO
X 100.
Here SiO2, Fe2O3, CaO, and MgO repre-
sent the percentage of these materials in
the melt. This relationship was found to
hold for widely varying ratios of Fe2O3
to CaO + MgO and to be almost completely
independent of the A12O3 content. The
relationship, admittedly an empirical
one, can be simplified still further to
the form
log (ri - 1) = 0. 066 (SiO2 percentage) - 1. 4
where rj is the viscosity in poises at 2600
F. A much more elaborate treatment of
this relationship was one of the useful
results of the recent work in England.
The rate of change of viscosity with
temperature also is relatively simple,
of the form
-0.1614
= (4.52 X 10 "4 t) - B
-------
Corrosion and Deposits From Combustion Gases
where rj is the viscosity in poises at
temperature t in degrees F, and B is
a constant fixed for each slag. The vis-
cosity at 2600 F can be inserted in this
equation to determine B, after which the
viscosity of the slag can be calculated
for other temperatures. Again, the
British have worked out a more elaborate
but equally empirical relationship.
At some point when coal-ash are cooled,
a solid phase separates which radically
affects viscosity by changing the flow
from Newtonian to pseudoplastic. Re-
lated to the liquidus temperature, this
is known as the "temperature of critical
viscosity" (Tcv) for coal-ash slags. At
this point, important changes occur in
flow behavior, and the slag may no
longer deform under gravitational forces.
This, in turn, greatly affects the thick-
ness of slag that can accumulate on the
furnace walls, the thickness being
greater as TCV is higher and as the New-
tonian viscosity is greater, all other
factors being constant.
The temperature at which this pseudo-
plastic behavior begins is related to
composition in a most complicated fashion.
No such simple relationship as the silica
percentage has been found to apply to
Tcv, which is also affected by such factors
as the rate of cooling of fluid slag. For
the present, it is enough to know that this
is an important factor in fixing the thick-
ness of slag on heat-receiving surfaces,
particularly where the temperature of
the slag is well below 2600 F. The
relationships here between slag accumu-
lation, coal-ash properties, and furnace
conditions are extraordinarily complex,
at least a dozen parameters being in-
volved. Little use has been made of this
analysis, largely because Tcv is not
related simply to composition and may
have to be determined experimentally for
each slag composition.
Oil Ash
Possibly because the ash content, of
residual fuels seldom is greater than 0. 1
percent, exceedingly low compared with
coal, the properties of oil ash have not
been investigated systematically. Sili-
cate minerals in crude oil vary r.mch
more widely than in coal ash, and A12O3
and Fe2C>3 also cover broad limits.
Alkalies may be high in residual fuel,
often because of contamination in refining
the crude oil, or in handling. Seawater,
unavoidably present in bunkering, is a
common contaminant in residual fuel.
Sulfur occurs in oil in a wide variety of
forms ranging from elemental sulfur to
such complexes as thiophene and its
homologues.
The uniqueness of most oil ashes is that
they contain, in addition to extraneous
materials, metallic complexes of iron,
nickel, and vanadium present as oil-
soluble organometallic compounds. These
are frequently porphyrin-type complexes,
so stable that temperatures in excess of
800 F usually are necessary to dissociate
them. As a result, they are difficult to
remove from fuel oil economically. An
undescribed scheme for removing essen-
tially all the nickel and vanadium from
residual fuel at a cost as low as 154, and even-
tually with enough excess air to V2O^.
The melting point and vapor pressure of
these oxides vary widely, with the re-
duced forms having a higher melting
point than the oxidized material. At the
high temperatures in flames, there is a
further tendency to produce a whole
series of vanadates, of which sodium
vanadyl vanadate, Na2O-V2O4 • 5V2O3,
is typical. Melting points vary widely
too, being only 1157 F for this compound.
-------
Corrosion and Deposits From Combustion Gases
Hence it is a liquid at the temperature
of superheater elements, thereby adding
to its aggressiveness in causing corrosion.
The fusion characteristics of oil ash are
poorly known. Cone fusion and other
arbitrary schemes such as hot-stage
microscopes have been used to check on
the melting characteristics of oil ashes,
but no systematic investigation has been
made as with coal ash.
EXTERNAL CORROSION
Tube wastage first posed serious problems
in boiler maintenance beginning about 1942,
when a sudden rash of wall- tube failures in
slag- tap furnaces was traced to external
loss of metal. In the worst cases, tubes
failed within three months of installation.
Measurements of tube wall temperature
showed that the tube metal was not over-
heated, typical maximum wall temperature
being 700 F. Heat transfer also was nominal.
The only unusual condition was that some
flame impingement appeared likely in the
affected areas.
It was soon found that an "enamel" was
present beneath the slag layer where
corrosion had occurred. This material,
which was found in thin flakes adhering
tightly to the tube wall, resembled a fired-
porcelain coating with a greenish blue to pale
blue color. These flakes of enamel were
moderately soluble in water, giving a
solution with a pH as low as 3. 0. They also
contained large amounts of Na2O,
and SOg, and were obviously a
complex sulfate. Following considerable
work in the laboratory, the "enamel" was
finally identified as K3Fe(SO4)3. There is
a corresponding sodium salt, as well as a
solid solution of these sodium and potassium
iron trisulfates.
Alkali ferric trisulfates were formed by
reaction of 803 with Fe2O3 and either K2SO4
or Na2SO4, or with mixed alkali sulfates.
At 1000 F, at least 250 ppm SO3 is necessary
for the trisulfates to form. At this tempera-
ture, neither the alkali sulfates nor the
alone will react with this concentra-
tion of SOg. Only when both the sulfates
and Fe2O3 are present will the reaction
occur. The trisulfates dissociate rapidly
at higher temperatures unless the 50%
concentration in the surroundings is
increased. Quantitative data are few, but
it appears that the concentration of 803
required to prevent dissociation of the tri-
sulfates at 1200 F to 1300 F, as would be
the case on superheater elements, greatly
exceeds any observed SO., levels in the gas
phase. Accordingly, some unique but as yet
unexplained action must go on beneath super-
heater deposits that can provide the equiva-
lent of, perhaps, several thousand ppm of
SOg in the gas phase. Lacking any better
explanation for the time being, "catalysis"
is usually blamed.
THE IMPORTANCE OF SO3
Any discussion of external corrosion and
deposits in boilers and gas turbines would
be meaningless without reference to the
occurrence of 303 in combustion gases.
Many investigators, both in the laboratory
and in the field, have studied the conditions
under which SO3 is formed, on the basis that
303 is a major factor both in high-
temperature corrosion and in low-temperature
corrosion and deposits. These studies
have been going on for more than 30 years.
The reasons are not difficult to state. In
the hot end of coal-fired equipment - furnace-
wall tubes and superheater elements, for
example - deposits taken from areas where
corrosion has occurred invariably contain
appreciable quantities of sulfates, some-
times as much as 50 percent reported as
SO3. Slag layers from the high-temperature
zone of oil-fired boilers also contain 803,
typically from 25 to 45 percent reported as
Na2SO4. In the 1959 Battelle report to
ASME, many examples are given of slag
deposits where there was more than 15
percent 803 in the deposit.
As has already been noted, the alkali iron
trisulfates cannot exist at 1000 F unless at
least 250 ppm of 803 is present in the
-------
Corrosion and Deposits From Combustion Gases
surrounding atmosphere, or the equivalent
803 level is provided some other way. At
higher temperatures, even more SO3 must
be present if these compounds are to form.
In the absence of SO3, the trisulfates could
not be produced and corrosion would not
occur.
Bonding of ash to superheater tubes
frequently attributed to a layer of alkalies
that condenses on the metal wall and serves
as the agent to attach the ash to the tube.
Further buildup of ash deposits, however,
depends on some other mechanism. One
explanation with fuels such as some subbi-
tuminous coals, lignite, and brown coal
containing large quantities of CaO in the ash
is that CaSO4 is formed. This substance,
well distributed in the ash deposit, is con-
sidered by many investigators to be the
matrix material that bonds the whole deposit
together into a coherent mass. Although
CaSO4 might be formed when CaO reacts
with SO2 and 03, it seems more reasonable
to expect that 803 is responsible.
At low temperatures, as in air heaters, there
is no question but that 803 is the major
offender. It combines with alkalies to plug
•air-heater passages, and if the metal
temperature is below the dewpoint, H2SO4
formed from SO3 condenses as a liquid film
on the metal surfaces to cause serious
corrosion. Acid smuts, where carbon
particles are saturated with this H2SO4, also
depend on the presence of 803.
These are the reasons why the formation of
SOs has been given so much attention. In
addition to the boiler manufacturers and the
fuel suppliers working in their own labora-
tories and in the field, Battelle has studied
the production of SOs in flames and by
catalysis for the ASME Committee on
Corrosion and Deposits. This work has pro-
vided a basic understanding of many of the
thermochemical reactions leading to
corrosion and deposits.
LOW EXCESS AIR
A revolutionary approach has been taken over
the past decade in Europe toward
eliminating the formation of SO3 in boiler
furnaces fired with oil by limiting the excess
air to an absolute minimum. Low excess air
seems to have been proposed first in
England as a means of decreasing corrosion
and deposits when burning residual fuel.
In 1960, Glaubitz in Germany reported
highly favorable results burning residual
fuel with as little as 0. 2 percent excess
oxygen. By carefully metering fuel oil to
each burner and properly adjusting air
shutters, he found it possible to reduce ex-
cess oxygen to as little as 0. 1 percent before
incomplete combustion became troublesome.
By operating at these low levels of excess
air, Glaubitz was able to operate boilers on
residual fuel for more than 30, 000 hours
without any corrosion and with no cleaning
being required.
Low excess air in oil-fired equipment also
has proven satisfactory in the United States
and is being used successfully in many large
boiler plants. Precise metering of fuel and
air to each burner has proven to be less
troublesome than had been expected earlier,
and in some instances with high furnace
turbulence ordinary controls have been found
satisfactory. In other cases, unburned com-
bustibles have made low excess air undesir
able. Sound principles guide the use of low
excess air, but applying these principles
usefully is still largely a matter of judgment
by boiler operators. It has been shown
repeatedly, however, that 50% largely is
eliminated, irrespective of the amount of
sulfur in the fuel, when the products of
combustion contain no more than about 0. 2
percent oxygen. At this level, the dewpoint
of the flue gas can be as low as 130 F where
the dewpoint for the moisture in the flue
gas is 105 F.
The important factors whereby low excess
air is beneficial include, in addition to a
decrease in SO3, a limitation on the oxida-
tion of vanadium. Low excess air leads to the
-formation of V2O3 and V2O4, which have
melting points much higher than V2O5. There-
fore, these reduced forms of vanadium are
considered less objectionable from the
standpoint of corrosion.
-------
Corrosion and Deposits From Combustion Gases
Work done recently in the laboratory shows
that the main benefits of low excess air, as
would have been expected, result from lack
of formation of 803. Flame studies have
shown that stoichiometric sulfur-bear ing
flames do not show the usual conversion of
part of the sulfur oxides to SOg by reaction
with oxygen atoms. Competing reactions
within the flame simply keep the oxygen-
atom level too low. Also, not enough oxygen
is present to convert an appreciable amount
of SC-2 to SC>3 catalytically on surfaces. The
result is an 863 level of only a few ppm with
a correspondingly low dewpoint, minimizing
troubles throughout the boiler, from the
superheater through the air heater.
Opinion at present is that corrosion and de-
posits when burning residual fuel can be
essentially eliminated by operating with
low excess air. Such procedures presumably
will not be possible with coal unless radical
changes are made in the combustion system.
In the meantime, studies of corrosion and
deposits continue in the search for still
better ways of eliminating these causes of
increased operating expense. Factors
involving the formation of SOs are now under-
stood fairly well. The next major step will
be to develop an equally good knowledge of
the mechanism whereby the trisulfates form,
the other complex metal sulfates that also
can be produced, and the role of vanadium.
Meticulous, well-planned research in the
laboratory and in the power plant will
answer those questions as effectively as it
has brought us to our present level of know-
ledge on the causes of corrosion and deposits.
-------
Section 3
BURNING OF SOLID WASTES
Chemical Analysis of Refuse Components
Terminology Used in Incinerator Technology
Classification of Waste to be Incinerated
Classification of Incinerators
Flue Fed, Industrial, Commercial and Special
Type Incinerators
Design Parameters for I.I.A. Incinerator
Classes IIA, III, IV, VI and VII
Operation Practices for I.I.A. Incinerator
Classes IA, IIA, III, IV and VII
Muncicipal Incinerators (I.I.A. Class V)
Municipal Incinerators - Design Parameters
Design Parameters for Municipal Incinerators
Municipal Incineration: Good Operating Practices
Good Operation Practices for Municipal Incinerators
Selected Publications
I.I.A. Incinerator Standards - 1966
Multiple-Chamber Incinerator Design Standards for
Los Angeles County
The Problems of Applying Incinerator Criteria
Discussion of "The Problems of Applying Incinerator
Criteria"
Combustion and Heat Calculations for Incinerators
Bibliography on Incineration of Refuse
-------
CHEMICAL ANALYSIS OF REFUSE COMPONENTS
Elmer R. Kaiser*
ABSTRACT
The proximate and ultimate analyses pf 20
constituents of municipal and commercial
refuse are presented, together with the
calorific values. The analyses are useful to
incinerator engineers as they are the basis
for calculating air requirements, flue-gas
volumes, and heat and material balances.
The analyses of components of refuse permit
the calculation of composite analyses of mixed
refuse from known proportions. Future in-
vestigations are suggested to obtain more
complete refuse data and to determine the
variability of municipal refuse.
INTRODUCTION
Millions of tons of solid wastes are burned
annually by communities, industries, agri-
culture, commercial establishments, and
residences. At least 4. 5 Ib of refuse are
generated daily per capita in U.S. cities.
•Incinerators to consume the refuse, range
from small batch-fed units to large municipal
plants with furnaces, each of which burns
over 10 tph, 24 hr/day, by continuous firing
on moving grates. The cost of the large
plants is upward of $4500 per ton-day (24 hr)
of capacity.
Modern engineering design of incinerators
begins with a known or assumed analysis and
weight of refuse. The refuse determines the
quantity of air required, the heat released,
the volume of flue gas produced, and hence
the size and proportion of ducts, flues,
chambers, and stacks. The variability of
refuse and the lack of interest in refuse as
a fuel for steam generation have caused some
delay in scientific studies of refuse. However,
interest in refuse analyses has recently in-
creased through the activities of the ASME
Incinerator Committee^1) and the investigations
in several European cities.
As refuse is usually a mixture of components,
the proportions of which will vary appreciably,
it was deemed advisable to determine the
analyses of the mure readily definable and
major components. The proportions of the
components could then be adjusted by the
reader to suit known or assumed conditions
of mixture.
Refuse may be thought of as consisting of
moisture, dry combustibles, and noncom-
bustibles. The major source of the dry com-
bustible portion originates in plant life. The
dry combustible in such items as paper, wool,
natural textiles, vegetable wastes, brush, and
leaves is largely cellulose (C6H10O5).
Cellulose has a calorific value of 7526 Btu
per Ib. Proteins, starch, and sugar associ-
ated with the cellulose have a minor depressing
effect on the calorific value^2) of this com-
bustible but may be included with the cellulose
in this grouping.
The second major class of dry combustibles
consists of hydrocarbons, fats, oils, waxes,
resins, synthetics (plastics and textiles)
rubber, linoleum, and the like. They have
high calorific values, ranging up to 19, 000
Btu per Ib and averaging about 16, 000 Btu
per Ib.
The air requirement and the calorific value
of the mixture of dry combustibles depend
primarily on the proportions of the lean and
rich constituents of these two classes. Meat
and cheese scraps, for example, are a mix-
ture of the high-Btu fats and lower Btu pro-
teins and carbohydrates.
Moisture contributes no heat units but it ab-
sorbs much heat on evaporation in the furnace.
Food waste and greens are high in moisture,
•about 75 per cent when fresh. They lose
moisture when exposed to the air or when
mixed with dry materials, such as paper.
Paper products, wood, and natural textiles
*Senior Engineering Scientist, New York University, New York, New York. Published in the
Proceedings of 1966 National Incinerator Conference
PA.C.ce. 31.9.66
-------
Chemical Analyses of Refuse Components
are hydroscopic and readily absorb moisture
until an equilibrium is reached with the sur-
roundings. Hence, special precautions must
be taken in sampling these materials to pre-
vent undetermined gain or loss of moisture.
The metals are not considered as combustibles,
but it is a fact that they oxidize in the fire to
varying degrees and thus produce hea't as
well as consume oxygen. They also gain
weight by oxidation, a fact that may be neg-
lected except for precision work.
The ash remaining after the combustibles have
been burned, together with dry mineral oxides
in the incinerator charge as in crockery,
bricks, glass, and dirt, may be considered
as inert.
TWENTY SAMPLES
Samples of 20 of the more important combus-
tible components of municipal refuse were
obtained from local sources at the time they
were being discarded and before contamination
from other refuse could occur. The gross
samples ranged between 5 and 25 Ib. The
samples were dried to equilibrium at 80°C
and reduced in size for final chopping in a
Wiley No. 3 mill. Samples of 10 to 20 grams
for the chemical analysis were taken from the
milled product. The particle size was under
2 mm.
The chemical analyses were performed by
Fuel Engineering Company of N. Y. in accord-
ance with ASTM Standard D-271-58. The
higher heating values were determined by
ASTM Standard D-2015-62T. The data from
the analytical laboratory were corrected to
the initial moisture content. For a discussion
on refuse sampling and analysis, the reader
is referred to the work of Etzel and
Table 1 lists the proximate analyses of 20
samples. The calorific values are given on
both the "as discarded" and dry bases. The
reader can readily convert to the moisture
and ash-free basis if desired.
The samples all showed a high loss of volatile
matter on heating in a closed crucible, which
is indicative of a need for much overfire air
and turbulence in the incinerator furnace. The
fixed carbon indicates the proportion of the
refuse that must be burned out on the grate.
The high moisture content of food ar.d greens
is in contrast to the low moisture contents
of paper. The high ash content of trade
magazines and junk mail is from the clay
fillers and sizing used in producing smooth
printing papers. A part of the ash content
of the leather shoe was from metal parts.
The heel and soil composition contained
mineral fillers.
The ultimate analyses of the same 20 samples
are reported on the dry basis in Table 2.
The analyses can be converted readily to any
moisture content if desired.
Carbon is the principal fuel element. In
cellulose (CgH10O5) the carbon content is
44.4 per cent, hydrogen 6.2 per cent, and
oxygen 49.4 per cent. Oxygen exceeds car-
bon in weight in some of the samples of paper,
which are principally cellulose.
Hydrogen is present in at least the amount
necessary to burn all the oxygen in the refuse
to water. In other words, the oxygen weight
is less than eight times the weight of hydrogen.
For convenience in combustion calculations,
the hydrogen in excess of that needed to con-
sume the refuse oxygen, (H - 0/8), is "avail-
able" to burn with combustion air. All the
carbon is deemed available for combustion.
Nitrogen is present in almost negligible
amounts except in components that contain
protein, which is 16 per cent nitrogen.
As sulfur is a necessary element in living
matter, refuse of plant and animal origin will
contain small amounts. Sulfur is added to
rubber for vulcanization. The sulfur content
of most refuse is low in comparison with
that of coal and oil. It may be assumed that
all the sulfur burns to sulfur dioxide (SC^),
although some is found in incinerator fly
ash'2), and further investigation may reveal
some trapping of sulfur in incinerator
residue.
-------
Chemical Analyses of Refuse Components
TABLE 1
PROXIMATE ANALYSES IN PER CENT BY WEIGHT. AS DISCARDED (A.D.) BY
HOUSEHOLDERS
1 • New ipaptr
2. Brown paper
3. Trad* mogoilno
4, Corrug. pap«r boxot
5* Ploitic coated papor
6. Waied milk cartons
7. Paper food cartons
8. Junk mail
9. Vegef. food wastes
10. Citrui rinds and leodl
11. Meat tcropi, cooked
12. Fried tat!
13. Leather ihoo
14. Hetl and lole composition
IS. Vacuum cleaner catch
16. Evergreen ihrub cuttings
17. Baliom sprue*
IB* Flower garden plant!
19* Lawn gran
20. Rip* tree leaves
Moisture
S.97
5.83
4.11
5.20
4.71
3.45
6.11
4.56
78.29
78.70
38.74
0.00
7.46
1.15
5.47
69.00
74.35
53.94
75.24
9.97
Volatile
Matter
61.12
B3.92
66.39
77.47
84.20
90.92
75.59
73.32
17.10
16.55
56.34
97.64
57.12
67.03
55.68
25.18 .
20.70
35.64
18.64
66.92
Ft.ed
Carbon
11.48
9.24
7.03
12.27
8.45
4.46
11.80
9.03
3.55
4.01
1.81
2.36
14.26
2.08
8.51
5.01
4.13
8.08
4.50
19.29
Btu/lb
Aih
1.43
1.01
22.47
5.06
2.64
1.17
6.50
13.09
1.06
0.74
3.11
0.00
21.16
29.74
30.34
0.81
0.82
2.34
1.62
3.82
A.D.
7974
7256
5254
7043
7341
l':27
7258
6088
1795
1707
7623
16466
7243
10899
6386
2708
2447
3697
2058
7984
Dry Basil
8480
7706
.1480
7429
7703
11732
7730
6378
8270
8015
12443
16466
7826
11026
6756
8735
9541
8027
8312
8869
TABLE 2
ULTIMATE ANALYSIS, DRY BASIS IN PER CENT BY WEIGHT
Refuse
Component
1.
2.
3.
4
5.
6.
7
8.
9.
10.
11.
12.
13.
14
in
16.
17
ia.
19.
20.
Newspaper
Brown paper
Trade magoline
Plastic coaled paper
Waxed milk cartons
Junk moil
Veget. food wastes
Citrus rinds and seeds
Meat scraps, cooked
Fried fats
Leather shoe
V 1
Evergreen trimmings
Flower garden plants
Lawn grass, green
Carbon
Nltrog
Sulfur
Aih
49.14
44.90
32.91
43.73
45.30
59.18
44.74
37.87
49.06
47.96
59.59
73.14
42.01
53.22
35.69
48.51
53.30
46.65
46.18
52.15
6.10
6.08
4.95
5.70
6.17
9.25
6.10
5.41
6.62
5.68
9.47
11.54
5.32
7.09
4.73
6.54
6.66
6.61
5.96
6.11
43.03
47.84
38.55
44.93
45.50
30.13
41.92
42.74
37.55
41.67
24.65
14.82
22.83
7.76
20.08
40.44
35.17
40.18
36.43
30.34
0.05
0.00
0.07
0.09
0.18
0.12
0.15
0.17
1.68
1.11
1.02
0.43
5.98
0.50
6.26
1.71
1.49
1.21
4.46
6.99
0.16
0.11
0.09
0.21
0.08
0.10
0.16
0.09
0.20
0.12
0.19
0.07
1.00
1.34
1.15
0.19
0.20
0.26
0.42
0.16
1.52
1.07
23.43
5.34
2.77
1.22
6.93
13.72
4.89
3.46
5.08
0.00
i2.86
30.09
32.09
2.61
3.18
5.09
6.55
4.25
COMPOSITE MUNICIPAL REFUSE
By calculation, the reader may combine
quantities of the components name, or add
others, and determine the proximate and
ultimate analyses, as well as the calorific
values of the mixtures. The analyses must
first be converted to the same basis as the
weights, such as "moist" or "dry. " The
weight of each component times the decimal
per cent of each element in it equals the
weights of the elements. The weights of the
elements, moisture, and ash are then totalled
separately. The totals of the elements can
then be related back to the grand weight total
to establish the composite analysis.
The total calorific value is the sum of the
calorific values of the components and is
higher than the Btu calculated from burning
-------
Chemical Analyses of Refuse Components
the same weights of carbon, net hydrogen,
and sulfur.
Municipal refuse is a varying mixture of the
20 components previously named and a large
number of minor components. The moisture
content is influenced by the weather, especial-
ly rain, despite the use of covered containers
and trucks. Refuse is also sprayed with
water at some incinerators to suppress dust.
Bacterial and enzyme action on moist refuse
also alters the analysis in time.
By way of illustration, a composite was
selected which was based on proportions of
the 20 ingredients plus others that have been
reported in published literature^2)'(4) and
obtained from private sources. The moisture
content was adjusted to a total of 20 per cent
by the addition of moisture, to bring the
moisture content into the range normally
experienced at incinerators.
Table 3 is the list of components and the per-
centage selected. Compared with older com-
positions, the selected group represents the
current compositions more closely through
an increase in paper and plastics and a re-
duction in ash and food waste. The reader
will understand the seasonal and regional
variability of such mixtures.
The proximate and ultimate analyses of the
composite were calculated by use of the data
in Tables 1, 2, 3 and previously published
values. The resultant analyses and calorific
values are given in Table 4.
The calorific value of the composite is the
sum of the contributions from each component.
As the metals are partly burned in municipal
incinerators, probably 50 per cent oxidized,
heat from that source should be added as was
done in Table 4. Where metals are not in-
cinerated, the heat from metals is to be
omitted.
As the data in Table 4 may be converted to
use for municipal refuse of other moisture
and ash contents, it is of interest to know
that the dry, ash-free combustible (60 per
cent of the refuse listed in Table 4) has a
higher heating value of 8766 Btu per Ib with-
out credit for the oxidation of metals, of 9070
Btu per Ib with credit for oxidation of metals.
The calorific values are influenced greatly
by the amount of fats, oils, and plastics
present.
TABLE 3
COMPOSITION AND ANALYSIS OF A COMPOSITE
MUNICIPAL REFUSE
Per
Cent
23.38 Corrug. paper boxes
9.40 Newspaper
6.60 Magoiino paper
5.57 Brown paper
2.75 Mail
2.06 Paper food cartons
1.98 Tissue paper
0.76 Plastic coated poper
0.76 Wax cartons
2.29 Vegetable food wastes
1.53 Citrus rinds and seeds
2.29 Meat scraps, cooked
2.29 Fried fall
2.29 Wood
2.29 Ripe tree leaves
1.53 Flower garden plants
1.53 Lawn gross, green
1.53 Evergreens
0.76 Plastics
0.76 Rags
0,38 Leather goods
0.38 Rubber composition
0.76 Points and oils
0.76 Vacuum cleaner catch
1.53 Dirt •
6.85 Metals
7.73 Gloss, ceramics, ash
9.05 Adjusted moisture
100.00
TABLE 4
ANALYSES OF A COMPOSITE MUNICIPAL REFUSE
Proximate Anorysis
Moisture
Volati le matter
Fixed carbon
Ash and metal
100.00 per cent
Btu/lb; 5260+ 182°= 5442
20.00 per cent
52.70
7.30
20.00
Ultimate Analysis
Moiiture
Carbon
Hydrogen
Oxygen
Nitrogen
Sulfur
Ash and metal
20,00 par cent
29.83
3.99
25.69
0.37
0.12
20,00
1 00.00 per cent
a From 50 per cent oxidation of metoll.
-------
Chemical Analyses of Refuse Components
THEORETICAL AIR
As one purpose of the analysis is to deter-
mine the theoretical or stoichiometric amount
of dry air required for complete combustion,
Table 5 is included.
TABLE s
THEORETICAL AIR REQUIRED
Carbon: 0.2983 « 11.53
N.I H: (0.0399-0.2569/6) « 34.3t
Sulfur: 0.0012 , 4.29
50 per cent of metalj: 0.0685 » 1.05
= 3.439 Ib
= 0.268
= 0.005
0.072
Total theoretical air par tb refuse = 3.784 Ib
Or 50.5 cu ft at 70F.
The total air supplied to incinerator furnaces
usually exceeds 2.25 times the theoretical,
expressed as 125 per cent excess air, to pre-
vent excessive temperatures.
When the air supply has been established, the
volumes of carbon dioxide, oxygen, nitrogen
and water vapor can be determined by con-
ventional textbook methods. The refuse
analysis provides much of the basic data
needed.
The analyses and calorific values of industrial
wastes, plastics, and synthetic fabrics are
needed as these materials will be present in
future refuse in larger amounts than today.
Data reported by C. A. Hescheles^5) indicate
calorific values up to 19, 840 Btu per Ib for
waste from a rubber-chemical industry.
The variability of municipal refuse is a
cause of much concern to incinerator
operators. Engineers may base a plant de-
sign on an average refuse analysis, but per-
formance falls off when the moisture content
of the refuse rises. Moisture content is the
most important refuse variable. By weight,
the water vapor produced by the example
refuse is 55. 9 parts to 109. 5 parts of carbon
dioxide. If the free moisture is doubled, the
total moisture increases to 75.9 parts. Air
moisture adds to the total.
A study of refuse variability is a major under-
taking by direct sampling and analysis. It
may be feasible to use new methods of monitor-
ing the flue gas for studying the subject
as most changes in refuse analysis are re-
flected in the gaseous products of combustion.
The heat released per pound of theoretical
air is useful in approximating the air require-
ment when only the calorific value of a refuse
is given. In the foregoing case, the Btu re-
leased per pound of theoretical air was 1417
without metals, or 1438 with metals. These
values are useful but are not precise for all
types of solid waste. For example, the Btu
released per pound of theoretical air is 1463
for corrugated cartons and 1424 for fried fats.
MORE REFUSE ANALYSES NEEDED
The sampling and analysis of refuse is a
promising field of investigation. Analyses of
refuse as it is burned at municipal refuse
incinerators should be obtained, as well as
calorific values for the analyzed samples. If
the refuse from which the samples are taken
is sorted, and the components are themselves
sampled and analyzed, the data will have
maximum value to others.
SUMMARY
Chemical analyses and higher heating values
of 20 refuse components have been presented
and their usefulness to incinerator designers
and operators has been described. A com-
posite municipal refuse was described in
which the dry combustible has a calorific
value of 9070 Btu per Ib, when credit is taken
for 50 per cent oxidation of the metals pre-
sent. Additional sampling and analysis is
recommended.
REFERENCES
1 Incinerator Committee, Process Industries
Div. (ASME), Proceedings of 1964
National Incinerator Conference, ASME.
New York. 1964.
2 Kaiser, E. R. Refuse Composition and Flue-
Gas Analyses from Municipal Incinerators.
Proceedings of 1964 National Incinerator
Conference, ASME, New York. 1964.
-------
Chemical Analyses of Refuse Components
3 Etzel, J. E., and Bell, J. M. Methods of 4 Municipal Refuse Disposal, Committee on
Sampling and Analyzing Refuse. APWA Refuse Disposal, American Public
Reporter, pp 2-4, 18-21, November, Works Assn. 1961.
1962.
5 Hescheles, C. A. Thermal Recovery
Systems from Burning Industrial Wastes.
Paper No. 64-WA/PIT)-ll, presented
at ASME Winter Annual Meeting. 1964.
-------
TERMINOLOGY USED IN INCINERATOR TECHNOLOGY
I FORE WARD
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.
7 Burners
Primary: A burner installed in the pri-
mary combustion chamber to dry and
ignite the material to be burned.
Secondary: A burner installed in the
secondary combustion chamber to main-
tain a minimum temperature 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
-------
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
-------
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. ( 23, above )
26 Incinerator
Equipment in which solid, semi-solid,
liquid or gaseous combustible wastes are
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.
REFERENCE
1 APCA publication. Vol. 15, No. 3, pp
125-126. March, 1965.
-------
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
5 Gaseous ,
liquid or
semi-liquid
wastes
6 Semi-solid
and solid
wastes
B.T.U.
of Aux. Fuel
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
Industrial
process wastes
Combustibles requiring
hearth, retort, or grat
burning equipment
Approximate
Composition
% by Weight
Trash 100%
Rubbish 80%
Garbage 20%
Rubbish 50%
Garbage 50%
Garbage 65%
Rubbish 35%
100% Animal
and Human
Tissue
Variable
Variable
e
Moisture
Content
%
10%
25%
50%
70%
85%
Dependent
on pre-
dominant
components
Dependent
on pre-
dominant
components
Incombus-
tible
Solids %
5%
10%
v4
5%
54
Variable
accord-
ing to
wastes
survey
Variable
accord-
ing to
wastes
survey
B-.T.U.
Value/lb.
of Refuse
as fired
8500
6500
4300
2500
1000
Variable
accord-
ing to
wastes
survey
Variable
according
to wastes
survey
of Waste
to be
included in
Combustion
Calculations
0
0
0
1500
3000
Variable
according
to wastes
survey
Variable
according
to wastes
survey
Recommended
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 f many sample . 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.
PA.C.ce.32.9.66
-------
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
-------
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. .
Ashpit Doori Step Oral
Figure 1. Incinerator Nomenclature
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 Coder Incinerators, Elk Grove"
Village, Illinois. (Prepared February, 1966).
PA. C.ce. 18. 7. 66
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.
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. LI.A. Standards contain
a chart and formula. L.A. shows a curve
according to the following equation:
R (Ib. /hr.)
AG ' LQ(lb. /hr. /ft. ^) = ft 2
Where AQ is the grate area, Rc 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.
-------
Design Parameters for 1.1. A. Incinerator Classes
C Arch Height
L. A. provides a formula as follows:
HA = 4/3 (AG) 4/n = 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.
Ill 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 HOO^F.
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 designed 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
-------
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 Hame 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
0
1500
3000
8000
and Organic
Wastes
Gaseous, Liquid
or Semi-Liquid
Wastes
Semi-Solid
and Solid
Wastes
(5000 Primary)
(3000 Secondary)
Variable according
to wastes survey
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. "
Note, that forced draft does not imply a
pressure in the primary chamber in relation
to the incinerator room atmosphere.
Tables 2, 3, and 4 which show barometric
damper sizes, chimney sizes, and air re-
quirements in the incinerator room as
specified by the 1.1. A.
-------
Design Parameters for 1.1. A. Incinerator Classes
Table 2
USE TO DETERMINE MINIMUM FREE AREA
OF BAROMETRIC DAMPERS
the Barometric Damper in
f Cross Sectional Area of Flue
r Stack
JOI&.O.VIVICDCDO-OOO — — >0
SUiSlnOlnOl/iOUiOlnOOto
° °° 45
S $§ 40
-------
TABLE 3
NATURAL DRAFT STACKS OR CHIMNEYS
(Minimum Recommended)
Incinerator
Capacity
in Ibs.
per hour
50
100
150
200
300
400
500
600
700
800 j
900
1000
Class III Incinerators
Type 1 Waste
Air**
Supply
350
525
700
1050
1400
1750
2100
2450
2800
3150
3500
Stack
dia.
14"
16"
18"
20"
22"
24"
26"
28'
30"
32"
34"
height*
30'
30'
35'
35'
40'
40'
40'
45'
45'
45'
45'
Type 2 Waste
Air**
Supply
250
375
500
750
1000
1250
1500
1750
2000
2250
2500
Stack
dia.
12"
14"
16"
18"
20"
22"
24"
26"
28"
30"
32"
height*
25'
30'
30'
35'
40'
40'
40'
45'
45'
45'
45'
Class IV Incinerators
Type 3 Waste
Air**
Supply
200
300
400
600
800
1000
1200
1400
1600
1800
2000
Stack
dia.
12"
14"
14"
16"
18"
20"
22"
24"
26"
28"
30"
height*
30'
30'
35'
40'
40'
45'
45'
50'
50'
50'
50'
Class VI Incinerators
Type 4 Waste
Air'*
Supply
90
180
270
360
540
720
900
Stack
dia.
9"
10"
12;
14"
16"
18"
20"
height*
25'
25'
25'
25'
30'
30'
30'
NOTES:
••Air supply is given in C.F.M. @ 70° F. and is the minimum which must
be available at all times in the incinerator room at atmospheric or a slight
positive pressure. The incinerator room or rooms should never be under a
negative or minus pressure. If the incinerator is charged from a room
other than the incinerator room the quantity of air shown must be avail-
able in both rooms.
The quantity of air shown must be increased to satisfy the following:
(1) If stack or chimney is higher than minimum to satisfy the larger baro-
metric damper involved.
(2) If any other equipment requiring air supply is located in the in-
cinerator room or charging room.
•The stack heights are based upon the following:
(a) Installation made at or near sea level.
(b) Stack heights measured from base of the incinerator.
(c) Incinerator is side charged.
(d) Breeching or flue connection not exceeding 10' in
length in a straight run or 3' including not more
than 1-90° bend or 2-15° bends.
(e) Stack extends not less than 3' above any roof within 75'
of the top of the stack.
The stack heighis must be increased or mav be decreased as
follows:
(I) Increase height 5;i per 1000' above sea level.
(2) Decrease height 25^ if slack is directlv on top of incin-
erator eliminating any brecihing or lli'ie connection.
(5) Increase height 15^ if incinerator is top charged.
(4) Increase height 15^ for eruh additional 10' of
straight breeching and 15fc for e:ich additional 90°
bend.
o
a
05
a
"s
a
o
o
•-!
O
-------
TABLE 4
INDUCED DRAFT FANS
(Minimum Recommended)
Incinerator
Capacity
in Ibs.
per hour
100
150
200
300
400
500
600
CLASS III INCINERATORS
Type 1 Waste
Air"
Supply
850
Ibs. per hour
flue
gases
1080
1275 | 1620
1700
2550
3400
4250
2160
3240
4320
5400
5100 6480
700 5'J50
7560
cooling
air
2160
3240
4320
6480
8640
10800
12960
15120
800 ; 6800 8640 17280
200 . 7650 ; 9720 19440
1000 8500 : 10800
21600
Fan
C.F.M.
@ 700° F.
1630
2hU5
3260
h890
6520
8150
9780
lllao
130UO
1^670
16300
"Cold" s.p.
,7
• .7
.72
.72
.75
.75
.75
.8
.8
.8
.8
Type 2 Waste
Air«»
Supply
600
900
1200
1800
2400
3000
3600
4200
4800
5400
6000
Ibs. per hour
flue
gases
768
1152
1536
2304
3072
3840
4608
5376
6144
6912
7680
cooling
air
1540
2310
3080
4610
6150
7680
9220
10750
12290
13830
15360
Fan
C.F.M.
@ 700° F
1130
1700
2250
3380
4500
5680
6750
78SO
9000
10130
11250 .
Qi]H" « n
68
.7
.7
.72
.75
.75
.75
.8
.8
8
fc
NOTES:
"see
re°BI
The total flue gases or total products of combustion are given in Ibs. per hour.
^ '"' h°Ur ^ " ^ ™ "^ l° ^ bled in'°
brcechfng'sectidn"' ^ h°Ur ^ " ^ ™ ^"^ l° ^ bled in'° a"d ""'""^ W'th 'he fluC gaSCS before enterinS lhe induced draft fan and
Tlie hn rapnciiy is given in C.F.M. @ 700° F. which is the anticipated temperature of the air-gas mixture entering the induced draft fan.
The st.uic pressure of the f.in is given as the "cold" (70° F.) static pressure and with the installaiion made at or near sea level. The static pressure at 700° F
is -la^ of the rold static pressure. Increase the "cold" static pressure S.5fl> for every 1000 feet above sea level. Pressure at /UU t.
Water sprays or a combination of water and air may be used to cool the flue gases before they enter the fan. The C.F.M. of the fan reduces but the static
pressure of the fan increases to overcome the resistance created by the gal washer or scrubber used. reduces but the static
d
n>
en
t-1-
•9
(U
3
c?
3
o
3'
rr>
u
3
"I
a
a
tfl
en
(B
en
-------
NOTES:
TABLE 4 (Contd)
INDUCED DRAFT FANS
(Minimum Recommended)
Incinerator
Capacity
in Ibs.
per hour
50
100
150
200
300
400
500
600
700
800
900
1000
CLASS IV INCINERATORS
Type 3 Waste
Air»»
Supply
485
728
970
1455
1940
2425
2910
3395
3880
4365
4850
IDS. per hour
flue
gases
625
938
1250
1875
2500
3125
3750
4375
5000
5625
6250
cooling
air
1250
1875
2500
3750
5000
6250
7500
8750
9000
10250
12500
Fan
C.F.M.
@ 700° F.
920
1380
1840
2760
3680
4600
5520
6440
7360
8280
9200
"Cold"s.p.
.7
.7
.72
.75
.75
.8
.8
.85
.85
.85
.85
CLASS VI INCINERATORS
Type 4 Waste
Air»»
Supply
200
400
600
800
1200
1600
2000
Ibs. per hour
Bue
gases
262
523
785
1046
1569
2092
2615
cooling
air
525
1050
1570
2100
3050
4200
5250
Fan
C.F.M.
@ 700° F.
385
770
1155
1540
2310
30SO
3850
.68
.68
.68
.68
.7
.7
.7
cooling ai,
The total flue gases or total products of combustion are given in Ibs. per hour.
a"d
with "le flue
bcf're
^ inuuced draft fan and
The fan capacity is given in C.F.M. @ 700° F. which is the anticipated temperature of the air-gas mixture entering the induced draft fan.
"The static pressure of the fan is given as the "cold" (70° F.) static pressure and with the installation made at or near sea level The sniic oressjre at 700^ F
u 45% of the "cold static pressure. Increase the "cold" static pressure 3.5ft for every 1000 feet above sea level. pn.ss.ire at ,00* F.
Water sprays or a combination of water and air may be used to cool the line gases before thcv enter the fan. The C.F M of the fan reduces but the ,nnr
pressure of the fan increases to overcome the resistance created by the gas washer or scrubber used. reiiuces but the static
O
ra
K
Q'
3
(0
0
1
t/1
o1
3
O
3'
O
O
1
n
-------
Design Parameters for 1.1. A. Incinerator Classes
Table5. I. I. A. Classification of Waste
to be Incinerated
TYPE I WASTE
Rubbish, consisting of combustible waste such
as paper, cartons, rags, wood scraps, sawdust, foli-
age, and floor sweepings from domestic, commer-
cial, and industrial activities.
This type of waste contains up to 25% moist-
ure, up to 10% incombustible solids, and has a
heating value of 6500 B.T.U. per pound as fired.
TYPE 2 WASTE
Refuse, consisting of an approximately even
mixture of rubbish and garbage by weight.
1 his type of waste is common to apartment
and residential occupancy, consisting of up to
50% moisture, 7% incombustible solids, and has
a heating value of 4SOO B.T.U. per pound as
fired.
TYPE S WASTE
Garbage, consisting of animal and vegetable
wastes from rcstnurants, cafeterias, hotels, hospi-
tals, markets, and like installations.
This type of waste contains up to 70% moist-
ure, up to 5% incombustible solids, and has a
heating value of 2500 B.T.U. per pound as fired.
TYPE 4 WASTE
Human and animal remains, consisting of car-
casses, organs and solid organic wastes from hos-
pitals, laboratories, abattoirs, animal pounds, and
similar sources, consisting of up to 85% moisture,
5% incombustible solids, and having a heating
value of 1000 B.T.U. per pound as fired.
TYPE 5 WASTE
By-product waste, gaseous, liquid or semi-
liquid, such as tar, paints, solvents, sludge, fumes,
etc., from industrial operations. B.T.U. values
must be determined by the individual materials
to be destroyed.
TYPE 6 WASTE
Solid by-product waste, such as rubber, plastics,
woodwaste, etc., from industrial operations.
B.T.U. values must be determined by the indi-
vidual materials to be destroyed.
XI AIR POLLUTION CONTROL
Basically, the incinerator built to either
1.1. A. or L.A. design parameters can be
operated to function at emissions well below
allowable limits. The 1.1. A. Standards
read, "The incinerators may be manually
operated and controlled provided that the
user has an operator in attendance a suffi-
cient time during operation to guarantee
functioning within the above limits, or in
lieu of such an operator, mechanical draft
regulation, fly ash collector, gas washer or
scrubber, and temperature control shall be
provided. " Where large incinerators are
used (1000 Ibs. per hour or over) in a
critical area, gas washers serve to reduce
dependence on the operator. The concen-
tration of the dust in the flue gas now may
not be as important as the total pollutant
emitted from the stack.
XII DESIGN VARIATIONS
Cognizance must be taken of studies on in-
cinerator design, operation, and related
performance made by the U.S. Public
Health Service (see references) which show
patterns for air admission, distribution and
effects of varying temperatures on gaseous
emissions and of unbound moisture on
particulate emissions. This data is impor-
tant to consideration of new parameters.
Also, important is to recognize the fact that
certain design innovations, if satisfactorily
tested, should be acceptable. In fact, we in
the industry are very conscious of a great
need for improvement and have written a
Section 5, DESIGN, into the 1.1. A. Standards
to accommodate such improvements. By
the same token, the 1.1. A. Standards are
regularly revised and a new issue to be
dated April, 1966, will supersede the one
used here (April, 1963) although for our
purposes of explanation, the old Standards
will suffice.
-------
Design Parameters for 1.1. A. Incinerator Classes
Class HI, TV and VI Incinerators with
capacities of 100 Ibs to 500 Ibs per hour
must have 4-1/2 inch firebrick lining and a
shell of 8 inch common brick casing or #12
ga. steel casing with 2 inch of hi-temp
insulating block. Incinerators with capaci-
ties over 500 Ibs. per hour must have 9
inch firebrick lining with 8 inch common
brick casing or #12 ga. steel casing with
2-1/2 inch thick hi-temp insulating block.
-------
INCINERATOR INSTITUTE OF AMERICA
QUICK CHECK CHART
-A PA CITY
LBSy
/HR
100
200
300
400
500
600
700
800
900
1000
€
T YPE
BURNING
RATE
2 6
30
32
34
35
36
37
38
38
39
GRATE
AREA
FT1
3.85
6.67
9.38
11.77
14.29
16.67
18.92
21.05
23.68
25.64
TOTAL
INCIN
26
52
78
104
130
56
182
208
234
260
1 WASTE
AREA IN
HI-VEL.
PASSFr»
40
.80
1.2
1.61
2 0 1
2.42
2.83
3.22
HI VEL.
PASS ~~-^
r'-^.-Ll^-'
GRATES
->
> '
/
f*
]
'I »» '
V-
3.63
4.03
AREA IN
LOW-VEL
1 57
3.13
4.70
6.27
783
9.40
10.97
12.53
14. IO
ISR7
GAS
TRAVEL
FT.
1 2 5
1.76
2.16
2 50
3.06
3.31
3.54
3.75
^ Qc,
BREECHING
OUTLET
^ 'l X
— ~.
'
—
/
7
\
/
~\
!>
TYPE 2 WASTE
BURNING
*,RATE
2 O
23
25
26
28
28
29
30
' ' LOW VEL.
PASS
__^- GAS TRAVEL
GRATE
AREA
FT1
8 70
12.00
15.38
18. 52
21.43
25.00
27.59
30.00
a
TOTAL
INCIN
VOL ,
FT*
36
54
72
90
108
126
144
162
M IN
AREA IN
HI-VEL.
PASSFf
5.7
8.57
.43
14,29
17.16
20.00
2286
2571
28.57
• .'j r/
/
/'
0)
7 .
, C
.'/'///
/
, 0.
-a
I
,
,•
/
•
/
,
PLAN
MIN
ARE A IN
-OW-VEL
PASSrTa
a22
3.33
4.44
5.55
6.66
7.77
8.88
10 00
II. 1
GAS
TRAVEL
FT
1. 05
1.48
1. 82
2 10
2.35
2.58
2 78
2.97
3.16
TY PE 3 WASTE
BURNING
RATE
16
18
20
2 1
22
22
23
2 3
24
GRATE
AREA
FT1
625
1 1. II
15.00
19.05
22.73
27.27
30.43
34.78
37.50
TOTAL
INCIN
VOL
FT1
14
28
42
56
70
84
98
I 12
126
MIN
AREA IN
HI VEL
24
48
72
.96
1.20
1.44
1.68
1.92
2.1 6
3.33 24 41.67 140 240
GRATE AREA = & X. *>
MIN AREA IN Ml VEL PASS « C.Xf
MIN AREA IN LOW VEL. PASS - Cx9
GAS TRAVEL h « I/T. f * I/T. e *d
*MEASURED IN HORIZONTAL PLANE.
MIN.
AREA IN
LOW VEL
PASSp-i
.93
1.87
2 80
3.73
4.67
5. 60
6.53
7.47
8.40
9.33
GAS
TRAVEL
FT.
964
1.36
1.67
1.93
2.16
236
255
273
2.89
3.05
BULLETIN D. .- 3
MARCH 1962
JOSEPH 80DER INCINERATORS
4241 NORTH HONOR! STREET
CHICAGO 13, ILL.
D
(D
ED
f
pi
3
B
tt
CD
°
O
3
D
a
n
u
g
9
o
en
-------
Design Parameters for 1.1. A. Incinerator Classes
REFERENCES
1 Rose, A. H. Stenburg. R. L., Corn, M.,
Horsley, R. R., Allen, D. R., and
Kolp, P.W. Air Pollution Effects of
Incinerator Firing Practices and Com-
bustion Air Distribution. JAPCA, 8,
297-306. February 1959.
2 Stenburg, R. L., Horsley, R. R., Herrick,
R. A. , and Rose, A. H. Effects of
Fuel Moisture and Incinerator Design
on Effluents from Incinerators. Proc.
52nd Annual Meeting APCA, Los
Angeles, California. June 1959.
3 Stenburg, R. L., Hangebrauck, R. P. ,
von Lehmden, D. J. , and Rose, A.H.
Effect of High Volatile Fuel on Incin-
erator Effluents. JAPCA, 11, 376-83.
August 1961.
4 Stenburg, R. L., Hangebrauck, R. P.,
von Lehmden, D. J., and Rose, A.H.
Field Evaluation of Combustion Air
Effects on Atmospheric Emissions
from Municipal Incinerators. JAPCA
12, 83-89. February 1962.
ADDENDUM: (Note: Enclosed is a Quick
Check Chart for incinerator
design used by Joseph Coder
Incinerators)
The purpose of the following chart is to pro-
vide a convenient way of checking our own
and our competitors'incinerators when
drawings or specifications are available to
see if the units meet the 1.1. A. Standards.
This chart will enable "on-the-spot" check
at the architect's or engineer's office. Data
not listed on this chart may be determined by
interpolation. As a specific example, if
capacity is 150 Ibs per hour of Type 1 Waste,
the burning rate would be determined by
adding 26 and 30 in the burning rate column,
dividing by two, and coming out with a fac-
tor of 28.
BURNING RATE: This is the amount of
refuse that can be consumed on each square
foot of grate area in each hour. It is
figured by dividing the capacity in pounds
per hour by the grate area in square feet.
GRATE AREA: As can be seen above, grate
area is determined by dividing the capacity
by the burning rate and is measured in a
horizontal plane as ^an be seen in the
sketch by dimensions (a) and (b). Grate
area for Type 1 Waste can include some
hearth but must not exceed 20% of total
burning area. Hearth area for Type 2
Waste can consist of 50% of the total burn-
ing area. When burning Type 3 Waste, the
grate area must not exceed 35% of the total
burning area. Where step grates are used
in lieu of hearth, they shall occupy at least
65% of the burning area surface.
TOTAL INCINERATOR VOLUME: Total
interior incinerator volume is exclusive
of the volume below the grates or hearth.
MIN. AREA IN HI-VELOCITY PASS: Mini-
mun area in the hi-velocity pass as shown
in the sketch is measured in a horizontal
plane although this minimum area should
be checked throughout the gas travel of the
Incinerator as no cross-sectional are inside
of the unit through which the gases pass
should be less than this area. This minimum
area is based on a velocity of 35 feet per
second at 1400°F.
GAS TRAVEL: The gas travel is a measure
of the distance the gases travel in a hori-
zontal plane in the low-velocity pass and in
the case of this sketch, it is the distance
between the center line of the two chambers
in the secondary combustion chamber of the
incinerator. This distance is figured by
taking the square root of the minimum area
in the low-velocity pass.
Other physical factors must be considered
when checking 1.1. A. Standards such as
wall construction, breeching size and con-
struction, chimney size, and the amount of
auxiliary fuel required. The most important
construction feature we mention here:
-------
OPERATION PRACTICES FOR I.I.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. I. I. 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.
I. I. 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
-------
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 do 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.
-------
MUNICIPAL INCINERATORS-DESIGN PARAMETERS
Leonard C. Mandell, P. E. *
I Introduction
This outline is intended to provide an under-
standing of what municipal incinerator design
considerations are, why certain parameters
have been devised, and what new parameters
appear to be needed. To gain this under-
standing, let us use the following approach
by:
1. Simply stating what municipal incinerators
are meant to accomplish,
2. Establishing pertinent design information
and parameters to accomplish this intent.
3. Evaluating and appraising just how well
the design, under actual operating conditions,
meets its intended purpose.
4. Discussing needed improvements in de-
sign and/or additional capabilities in order to
develop municipal incineration to the state
where it becomes an effective, solid-waste
disposal method.
II Municipal Refuse vs. The Incineration
Process
A. The Refuse
Today's American urban society generates
relatively large amounts of solid waste mate-
rials. It is estimated that approximately five
Ibs. of municipal refuse is produced per capi-
ta per day. This does not include the thou-
sands of tons generated annually by the many
industrial or redevelopment, demolition-type
operations, which may actually increase the
five Ib. per capita rate by 50-100%. The
American Public Works Association itemizes
and describes these materials shown in Table I.
Accordingly, municipal refuse may be de-
fined as "any discarded solid-waste material
arising in significant quantities, from the
myriad of daily, conventional, human activ-
ities occurring within the confines of a munic-
ipality. "
Table II lists the refuse contents of a typical
municipal incinerator as received. The proxi-
mate analysis of a mixed refuse may be as-
sumed as:
Volatile s
Fixed Carbon
Moisture
Ash, metal and glass
53%
7
20
20
The heat content for this refuse (1966) may be
taken as 5500 Btu/lb. as received. Its stoi-
chiometric-air value is 3. 8 Ibs. of dry air/lb.
of refuse as received.
It is important to note that although many of
the small household noncombustibles such as
cans, bottles, and ashes are included in re-
fuse charged into the incinerator--they are
also discharged without disposal as part of
the residue or ash.
B. The Municipal Incineration Process
The municipal incineration process was first
attempted in England approximately 90 years
ago.
The literal definition of "incinerate" means
to burn to ashes. Burning implies fire and
heat. Ashes refer to the solid residue after
burning of the combustible material is com-
plete.. Fire is a manifestation of flame com-
bustion with its generation of voluminous
amounts of gases. Hence, incineration (as a
perfect process) may be defined as "the con-
version of combustible wastes (by flame com-
bustion) to an inert residue and hot oxidized
gases. " Therefore, municipal incineration
implies the application of the incineration
process under controlled conditions to con-
vert the municipal refuse to ashes and gases.
PAC Ce 40.1.69
-------
add 3
Table I
REFUSE MATERIALS BY TYPE COMPOSITION. AND SOURCES-'
Type
Composition
Sources
Garbage
Rubbish
Ashes
Wastes from preparation, cooking and serving of
food; market wastes; wastes from handling, storage,
and sales of produce.
Combustible: paper, cartons, boxes, barrels, wood,
excelsior, tree branches, yard trimmings, wood
furniture, bedding, dunnage.
Non-combustible: metals, tin cans, metal furni-
ture, dirt, glass', crockery, minerals.
Residue from fires used for cooking and heating and
from on"-site incineration.
Households, restaurants, insti-
tutions, stores, markets.
Street Refuse
Dead Animals
Abandoned. Vehicles
Sweepings, dirt, leaves, catch basin dirt, contents of
litter receptacles.
Cats, dogs, horses, cows.
Unwanted cars and trucks leftjanjgublic property.
Streets, sidewalks, alleys.
vacant lots
Industrial Wastes
Demolition Waste
Food-processing wastes., boiler house cinders,
lumber .scraps, metal scraps, rubber, plastic,
shavings.
Factories, power plants.
Lumber, pipes, bricks, masonry, and other con-
struction materials from razed buildings and other
structures. •
Demolition sites to be used for
new building, renewal projects
expressways
Constyuc-tLp'ri Wastes
Special'-Wastes
Scrap lumber, pipe, other construction materials.
Hazardpus solids and liquids: explosives, patho-
l.ogical wa"ste, radioactive material.
New construction, remodeling.
Households, hotels, hospitals.
institutions, stores.
industry.
Sewage. Treatment.
J3e sidue
§plids from course screening and from grit chambers;
septic tank sludge. |
Sewage treatment plants;
septic tanks.
*With, permission of Public Administration Service and American Public Works Association.
-------
Table II
COMPOSITION OF A TYPICAL MUNICIPAL REFUSE
HHV(a)
Btu/lb
MAF Basis(c)
Garbage
Corrugated paper boxes
Reading papers
Brown paper, food-cartons, tissue paper
Waxed papers and cartons
Vegetable and fruit wastes"
Cooked meat/fat scraps
Wood
Garden trimmings, leaves, grass
Plastics
Rags
Leather goods
Rubber composition
Paints and oils
Dirt "1
Metals L noncombustible = 16. 8%
Glass, ash, ceramicsl
Adjusted water
Wt %
7900
7300
16,200
8400
8600
15,000-18, 000
12,500
Stoic hi ometric
Air Needed"3'
Ibs/lb
MAF Basis
5. 9
5. 5
12. 1
6. 3
6. 5
100. 0
(a) High Heating Value
(b) Based on . 75 Ibs. air/ 1000 Btu.
cellulose results.
(c) Moisture-Ash Free Basis
If assumed as all cellulose, then a stoichiometric value of 5. 1 Ibs. air/lb
-------
Municipal Incinerators - Design Parameters
11 should be noted that approximately 50-100
times (by weight) more gases than ashes arc
c reated.
The nature of the man-made combustion-pro-
cess tends towards inefficient burning with the
liberation of smoke soot, fly-ash, complex
hydrocarbons in vapor, gas and droplet forms,
organic acids and other gaseous sulfur and
nitrogen oxides--and a residue which is far
from being completely mineral/ash. In fact,
today's most advanced thermodynamic tech-
nology cannot simultaneously burn more than
one of our best-prepared, homogeneous fuels
in the same furnace with any degree of satis-
factory performance and efficiency.
As you know, much of the municipal refuse
is not suitable as incinerator-fuel due to its
bulkincss and noncombustible nature (cans,
metal-furniture, glass, dirt, ashes, etc.)
Further, the make-up of many of the combus-
tible items is extremely variable in size,
weight, contamination, protein and organic
composition, moisture, heat content, burning
characteristics, etc. Hence, this should give
us some idea of some of the difficulties to
expect from the incineration of municipal
r e f u s e.
C. The Intent and the Compromise
It is obvious that an incinerator capable of
converting all municipal refuse to an inert
ash in an efficient, feasible manner compat-
ible with the public health would be most
desirable. The inherent nature of the incin-
eration process vs. the characteristics of
municipal refuse, in light of today's technol-
ogy, indicates that an incinerator should im-
ply the concept of a facility that contains the
ability to accomplish this. This does not im-
ply a (one) furnace system which we now have
with all of its excessive costs, too much
maintenance, and air pollution problems. It
does mean an arrangement of several differ-
ent types of furnaces and incinerators with
such prc-treatment and after-treatment as
size reduction, separation, particulate ar-
restance, pollutant gas removal, etc. , re-
quired to attain the stated objective.
The current practice, which is just starting
to change, is to have one furnace design to
handle the small combustible and household
non combustibles from the general popula-
tion and the garbage/paper type commercial
and industrial wastes. Investigation discloses
that this amounts to only 20-25% of the munic-
ipal refuse generated.
Hence, by the evolution of events occurring
during the past 90 years, the purpose of a
municipal incinerator is mass reduction and
conversion of small combustible household
wastes and commercial/industrial paper/
garbage wastes to an inert mineral residue
and in the process accept at times small non-
combustible refuse; items like cans and bot-
tles in order to provide the small handling
and cost savings of a separate pickup.
The compromise is that "this is being done
in an efficient, costly manner with the depend-
ence on an ancillary burial site together with
the pollution of the immediate atmosphere by
5-10 times (by weight) of refuse burned, and
over 50-100 times (by weight) as much pollu-
tants as ashes created. " It should be noted
that a new trend is just now developing in the
United States, and that is to have separate in-
cinerators for specialized applications: e.g.
the Dupont type pit incinerator for combus-
tible demolition, skids, debris and industrial
wastes; and the Detroit garage-type inciner-
ator for brush, log and tree type wastes.
These facilities are being added as separate
entities usually on the general incinerator
ground- site.
Ill Design Considerations/Parameters
A. Basic Requisites
Regardless of the incineration capability of
the facility, the entire operation from refuse-
receiving through ash-disposal must be ef-
fected in a safe, sanitary and feasible manner.
This means in fact that the public health as-
pect of air pollution must be sufficiently con-
trolled beyond doubt; also, the reduction/con-
version process must be effective and its over-
all installation and operating cost reasonable.
Further, adjacent property should not be dam-
aged from soiling or corrosion nor should
their owners suffer from real estate devalu-
ation.
-------
Municipal Incinerators - Design Parameters
B. Parameters
In general, if you and I were charged with the
responsibility of designing an incinerator, we
would be concerned with at least the following
aspects:
1. Land requirements/area
2. Zoning
3. Roads, access
4. Raw storage/odor control
5- Turning
6. Charging
7. Ignition chamber
8. Secondary/expansion chamber
9- Overfi re/uncle rfi re air/draft
10. Ash removal
11 . Flue gas cleaning
12. I. D. fans
13. Breeching
14. Chimney
15. Auxiliary fuel burners
16. Instrumentation
17. Materials of construction
18. Air Pollution
19. Water wastes
20. Economics
An engineering parameter may be defined as:
"a consideration of an independent nature that
can be used as a measure of related, depend-
ent variables, " i. e. , burning rate as a para-
meter helps to determine the grate area and
grate speed within a furnace; chimney draft
as a parameter helps to determine the allow-
able flue-gas velocities, breeching cross-
sections, and other flow-energy, absorbing
occurrences: Heat release may be equiva-
lent to combustion chamber volume; percent-
age carbon dioxide as a parameter is equiva-
lent to combustion efficiency; grain loading
is equivalent to the effectiveness of air pollu-
tion control. For the lecture at hand, the
following parameters will be discussed: pub-
lic health and economics, receiving and stor-
age, charging, burning, draft, ash, and occu-
pational health.
C. Public Health and Economics
Site Selection
Engineering and planning considerations to-
gether with public opinion and acceptance
dictate the location of a proposed facility.
The controlling factors are those of econom-
ics and the public health. Economics concern
the installation and operating costs, the cost
of hauling the refuse, the disposal of th;j ash,
the adaptation of the site such as access roads,
water and sewage problems, topography modi-
fications, soil problems, aesthetic treatment,
and the loss to neighboring taxpayers from
air pollution damage and devaluation to their
oroperty. The adverse consequences to the
•.uiblic health of living within an environment
that receives literally hundreds of tons of
rcspirablc air pollutants daily is not known.
However, the inhalation of many metallic
parliculates is known to have serious respir-
atory etiology and these pollutants are emitted
from municipal incinerators. The psychoso-
matic and psychological effects of mental un-
happiness arc also associated with such pollu-
tants as objectionable and nuisance odors or
the obscuring of the sunlight by light-scattering
plumes. The synergislic action of low concen-
trations, especially on the aged, the allergenic
and the ill, is not known.
No hard and fast rule has been set for land
area requirements. However, a typical plant
may use between 100-500 square feet or more
per nominal ton of rating.
D. Refuse Generation
Custom has evolved the measure of "tons per
day" to express the size of a municipal incin-
erator plant. This refers to the design burn-
ing rate in short tons per 24 hours. A 150 ton
furnace has an hourly design burning rate of
12, 500 Ibs. of refuse per hour. The size of a
plant should be based on a valid appraisal of
the anticipated load that will result from the
population and the expected commercial and
industrial refuse forecast for 25 years in the
future. Once this load rate is established,
the incinerator may be sized. The designer
together with responsible members of the
community have the choice of setting up work
schedules that usually vary from 8-10 hour
shifts. Present day design is based on the
value of 4. 5 Ibs. /capita/day of refuse being
received for municipal incineration. Hence,
a city with a population of 200, 000 would plan
for a 450 ton/day plant. Reflection will indi-
cate that three 150-ton/day furnaces will afford
the important advantages of flexibility in oper-
ation, cost savings in maintenance and con-
tinued operation in the event of furnace failure
or needed repairs. It should be noted that as
of 1967, the size of municipal incinerators
ranged between 50-1200 tons/day and furnace
sizes ranged from 30-400 tons/day.
-------
Municipal Incinerators - Design Parameters
E. Receiving and Storage
1. Scale
Efficient incinerator opt-ration requires the
maintenance of accurate records whicii in-
clude the quantity ann trues ot refuse to be
burned. Upon arrival ...t thf ticility. all
trucks should be weighed to obtain the net
weight of the refuse. At that time, the type
of refuse, its source, the truck identification,
date and hour should be noted. A typical scale
manufactured by Fairbanks Morse prints and
indicates the net weight, date and hour. A
typical scale has a dual range of up to 30, 000
and 60, 000 Ibs. , and should be located near
the main building adjacent to the tipping floor
area.
i. Tipping Floor
All refuse received at the plant is dumped into
storage pits prior to being fed into the furnace.
The approach area or apron where the packers
and trucks tip their bodies for dumping is
called the tipping floor. The floor should ex-
tend along the entire pit so that several trucks
can unload at the same time. The floors
should be made of dense, reinforced concrete
with ample drainage. See Photo 1.
3. Storage Prior to Burning
The nature of combustible municipal refuse
requires dense, reinforced concrete for ro-
dent and ground water protection. Good drain-
age and provisions for extinguishing pit fires
are also needed. Present de-sign calls for 1-2
days of storage as related to the plant design
capacity. Refuse as received varies between
300-700 Ibs. /cubic yard with an average of
approximately 450 Ibs. /cubic yard (17 Ibs. /
cubic foot for wrapped household garbage).
Hence, the 450 ton plant would have a storage
(360 Ibs. /cubic yard for combined refuse) pit
volume between 1000-2000 cubic yards (27, 000-
54, 000 cubic feet). Odor and decay will occur
in the pit if the refuse is held too long (over 3
days)--especially in warm weather. Exhaust
ventilation with activated carbon treatment will
control these odors from an air pollution con-
trol standpoint. See Photo 2.
PHOTO 2
F. Charging
PHOTO 1
The introduction of the refuse into the furnace
ignition area will influence the burn-out effi-
ciency and the amount of suspended solids en-
trained with the moving flue gases.
Direct, periodic "drops" from overhead hoppers
via electric or hydraulic or pneumatic charging
gates have been common for the smaller size
furnaces (100 tons/day). Continuous feed via an
-------
Municipal Incinerators - Design Parameters
inclined transfer-grate provides pre-drying,
better combustion, and less air pollutants. The
refuse is conveyed from the storage pits to the
charging hoppers by overhead cranes which use
clam buckets and/or grapplings.
vary from 1-4 yards/grab. Bridge
cranes are best and standard usage is one
for every 500 ton/day rating. Popular grap-
ple sizes vary between 1 1/2 and 2 1/2 cubic
yards. The maximum size is approximately
5 cubic yards.
G. The Burning
Burning of the refuse begins in the ignition
zone of the primary combustion chamber.
Today's drier material burns faster and with
greater heat release. Hence, most of the en-
tire combustion occurs in the primary chamber
with final oxidation of the carbonaceous par-
ticulates and entrained-fly occurring in the
secondary chamber.
1. TheFUrnace
The furnace normally refers to the enclosed
refractory-lined chamber which includes the
transfer grate, the hearth, the main grate,
and the ash drop area. At present, there are
three different types of furnace designs:
(a) the cylindrical batch feed, 'b) the unit cell
batch type, and (c) the continuous feed/mech-
anical grate furnace. (Note: Batch feed fur-
naces are limited to the size of 250 ton/day.
The larger modern incinerators are using
the continuous mechanical grate that employs
either some type of rocking, oscillating, or
reciprocating mechanism or the travelling
type grate that moves the burning, agitated
refuse along at a controllable rate to the ash-
drop location. )
Operating temperatures (which are propor-
tional to the completeness of combustion and
percent excess-air admitted) range from
1000 - 2000°F. , with 1600 - 1700°F. as the
preferred set-point. The maximum desirable
is 2000 F. because of refractory deteriora-
tion and inability to withstand ash fusion
effects related to the mineral components
(clay from papers) of the refuse. See Photo
2A. (Note: Water-cooled metal walls lower
the normal 150-300% excess air requirements
down to 50-60%. )
PHOTO 3
A few comments on refractories are in order:
Refractories are calcium aluminate type, fire-
clays in the forms of brick, plastic, and cast-
ables. Important properties are Pyrometric
Cone Equivalent (PCE), spalling, thermal ex-
pansion, and porosity. Super duty clays have
PCE of approximately 34, while silicone car-
bide has the best slag resistance. This is one
of the real problems in refractory mainten-
ance because of the cost of refractory replace-
ment caused by the accumulation of slag.
Slag adheres tenaciously, damages the refractory
and obstructs flue-gas passages.
The furnace dimensions are sized according
to two parameters: (a) the grate-loading or
burning-rate and (b) the heat-release volume.
Mixed refuse of garbage, rubbish, and non-
combustibles burns at a rate of 75 Ibs. per
hour per square foot of grate for continuous
feed, and 110 Ibs. per hour per square foot
for batch feed. Combustible rubbish alone
has a design rating of 50 Ibs. per hour per
square foot for continuous feed, and 35.Ibs.
per hour per square foot for batch feed. As
a rule, in the newer furnaces, a burning rate
of 300, 000 Btu per hour per square foot of
grate area for continuous feed, and 400, 000
Btu per hour per square foot for batch feed,
and 20, 000 Btu per cubic foot heat release are
followed. It should be noted that residence
time is proportional to the furnace size and
gas velocity through the furnace. It should be
noted also that the trend is for combined igni-
tion and primary chambers with 35-40 cubic
feet of total volume per ton refuse burned.
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Municipal Incinerators - Design Parameters
2. Thi! Secondary Combustion Chamber
The purpose of this chamber volume is to
provide the additional time, temperature, and
turbulence and oxygen to complete the com-
bustion of the organic portion of the refuse. It
should be noted that a small amount of solid
deposition of inorganic material also occurs
in the chamber because gas velocities are
normally sized for under 2000 feet per minute
at 1800°F.
Such items as air jets, bridge wall, and cur-
tain wall may be part of this chamber. Their
purpose is to alter the direction of the flue
gases for better mixing and turbulence, also
baffle impingement and settling of the large
fly-ash. The leaving-cnd of the chamber usu-
ally leads to some type of suspended, solid-
arrestance assembly.
H. Suspended Particulate Arresters
This is one area of municipal incinerator de-
sign that did not receive its share of impor-
tance until the early 1960's. The increase in
the number of incinerators and the growing
apprehension of chronic illness associated
with air pollution have brought this about.
The earlier designs, say until I960, used little
or nothing in the way of air pollution control
equipment. The accepted device which in fact
had little or no merit was the settling or sub-
sidence chamber (velocities under 600 feet per
minute could be maintained) which removed no
more than 5 percent of the significant particu-
late pollutants. The next so-called improve-
ment consisted of water-spray nozzles which
removed about twice the pollutants, but unfor-
tunately added a large quantity of water vapor
to the flue gas. In the writer's opinion, this
could at times be worse than if not used at all,
because of the wetting of the fine solid aero-
sols. Their presence could be corrosive and
injurious to health and property. In 1964, the
wetted-baffle impinger displayed the first sig-
nificant improvement. It removed approxi-
mately 50 percent of the significant suspended
matter. Recently, the smaller diameter multi-
clone collectors (12-18") have shown promise
with collection efficiencies approaching 80 per-
cent. As far as the United States is concerned,
this is the situation at present. The most pop-
ular fly-ash control methods in the United
States now, are water sprays with wet bottom
and baffles. Electroleclic precipitate rs used
in Europe are now being evaluated and arc ex-
pected to provide arrestance in excess of a
95% U-vcl.
I. Draft
1. Breeching
All connecting flue gas conduit between the
exit of the incinerator proper and the inlet
to the chimney can be called the breeching.
This flue or duct is refractory-lined for pro-
tection of the metal shell. Duct velocities
rarely exceed 3000 feet per minute. Good
design is 2000 feet per minute. It is con-
trolled by available draft -- either natural
or induced.
2. Dampers
The inherent variability of the refuse and the
thermodynamic characteristics of the burning
process require some control of air move-
ment into the furnace. The rate and path of
flue-gas travel through and out of the inciner-
ator is also important. Refractory-lined or
water-cooled type dampers are used. As a
rule, a draft over the fire of 0. 06 "W. C.\ 02"
will be adequate.
3. I. D. Fans
In systems where the overall pressure loss/
energy requirements are greater than those
attainable with conventional chimney draft,
induced draft fans are used. They may be
driven by electric motors or steam turbines.
?ee Photo 3.
4. Chimneys
Besides creating the driving force to over-
come draft and flue-gas flow requirements,
chimneys provide an excellent mechanism
for high altitude dispersion of incinerator
emissions.
Chimneys are double-wall units with an in-
terior refractory heat-resistant lining and
exterior shell of wedge-shaped (radial) brick-
work or carbon steel plate; when chimney
heights exceed 200 feet and inside diameters
-------
Municipal Incinerators - Design Parameters
PHOTO 4
approach 8-9 feet, then reinforced concrete
shells become feasible. They provide excel-
lent structural strength but suffer from ther-
mal and plastic stress cracking.
An important consideration in chimney work
is the heavy bearing imposed on the soil from
static and wind forces. Another important con-
sideration is the cost of chimneys. They are
expensive.. .about 7% of the total incinerator
cost.
Every chimney requires certain accessories
such as lightning protection, aircraft lighting,
test openings, clean-out doors, ladders, cat-
walks, and caps. Test openings are important.
They should be 6 inch diameter pipes which ex-
tend through both interior lining and exterior
shell. At least two ports, set at 90° of each
other, are normally sufficient.
J. Ash Handling
From 5-25 percent of the refuse charged into
the incinerator emerges as ash (not counting
its wet weight). It consists of unburned
material, ashes, cans, bottles, and other non-
combustibles (average wet weight of 100 Ibs. /
ft ). Ash must be removed from the grates
and furnace-proper at a required rate. It is
usually water-quenched to eliminate fires,
smoke and odors, and most important, it re-
quires burial at a suitable disposal site, since
it may contain a significant amount of organic
material.
The preferred quenching method employs the
water trough with an endless drag-type chain
conveyor that scrapes the ash up into an over-
head hopper for unloading into a truck.
K. Occupational Health
Ventilation should be incorporated for odor and
dust control in the storage pit and charging
area and the operating floor for ambient space
control of heat and smoke. Some of the pit
exhaust can be used for combustion air. The
balance can be filtered and adsorbed or oxi-
dized for odor control. The exhaust air from
the operating floor can be discharged to the
atmosphere without any treatment.
Apart from the conventional considerations of
natural ventilation, lighting, and sanitary facil-
ities and those of accident prevention from lad-
ders, catwalks, etc. , due consideration should
be given to the fire and explosive nature of cer-
tain dangerous materials: solvents, finely di-
vided organic dusts and sealed aerosol contain-
ers which explode with sufficient pressure to
cause serious personal injury and equipment
damage.
L. Air Pollution Considerations
Evidence is accumulating from biostatistical
and epidemiologic experiences, and from
acute episodes and laboratory experiments to
show that meaningful relationships exist be-
PHOTO 5
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Municipal Incinerators - Design Parameters
tween air pollution and respiratory illness,
and that at the present time, adequate health
standards do not exist. Hence, it appears
prudent as a precautionary measure to use
the best feasible control methods to reduce
suscepitble pollutants. See Photo 4.
When it is realized (1) that 80-85% of all re-
fuse charged into the incinerator is discharged
as the conventional flue-gas of carbon dioxide,
carbon monoxide, water vapor, sulfur oxides,
and nitrogen oxides, and (2) that a myriad of
other gases and fumes such as hydrogen chlo-
ride, hydrocarbons, tin, zinc, iron, chromium,
vanadium, and many other metallic oxides as
well as smoke accompany these discharges,
(3) that a conventional size municipal inciner-
ator (480 ton/day, servicing about 250, 000
population) releases approximately 300, 000
Ibs. (4, 000, 000 standard cubic feet) of these
flue-gases/hour, and (4) that normal atmos-
pheric diffusion and turbulence will pollute at
least 10-100 times this space, it indicates that
a hard look, one free of apathy or prejudice,
must be taken of the air pollution aspects.
IV. On Meeting the Needs
A. In General
Present municipal incinerator design does not
adequately fulfill the needs of today's densely
populated, waste-generating urban society. As
stated previously, current equipment converts
and reduces only approximately 20-25% of the
total solid waste-generation rate, and it does
this at an excessive cost. The urban incinera -
tion operation is contributing significantly to
the endemicity of chronic respiratory illness.
It also acts as a retardant to the promotion of
the well-being and public health of the commu-
nity in which it is located.
B. Accomplishments
As expensive and as inefficient as it is, cur-
rent municipal incinerator design does at
least handle the current pressure of size-re-
duction and conversion of decomposable organ-
ic material in highly populated areas.
1. It reduces the bulk volume of raw munici-
pal refuse by approximately 80-90%.
2. It reduces the weight of raw refuse by 75-
90%.
3. It provides the greatest volumetric reduc-
tion of the available reduction methods.
4. Provides the most rapid conversion (with-
in minutes) of combustible cellulose, animal,
and hydrocarbon materials to reasonable min-
eral residue.
5. Provides sufficient mass - reduction within
the ability of urban areas to dispose of the in-
cinerator residue so that it has become the
method of choice of most cities where air pol-
lution has not become critical.
C. Deficiencies
1. A relatively inefficient combustion process
with approximately 10-25% of original weight
requiring subsequent land disposal, so that
additional land area is needed.
2. Emits to the atmosphere 50-100 times as
much polluted gases as refuse incinerated and
50-100 times as much flue gases as ashes,
thereby constituting, in the writer's opinion,
a significant ai r-pollution source.
3. The most expensive "so-called disposal
method" costing $6000 to $8000 per ton of
rating to build, and approximately $5. 00 to
$6. 00 per ton for operation and maintenance
as compared to sanitary land fill at $1. 50 to
$2. 50 per ton for disposal.
4. Requires an undue amount of operational
control, instrumentation, and maintenance.
V. Improvements Needed to Make Municipal
Incineration a True Solid Waste Disposal
Method
A. Relative to Combustion Process
1. Better fuel, more homogenous, perhaps
requiring sorting or removal of bottles, cans,
dirt, ashes; size reduction; continual turning
and mixing, etc.
10
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Municipal Incinerators - Design Parameters
2. Better control of thermodynamic condi-
tions within the furnace such as fuel/air con-
tact, turbulence, and ambient temperature
over the fire.
3. Better automatic control via instrumen-
tation for primary and secondary air quantities,
injection targets, and grate speeds.
4. More consistent and better burn-out to ob-
tain efficiencies close to expected mineral con-
tent regardless of refuse composition in order
to reduce loading, hauling,and burial require-
ments.
5. Better burn-out of airborne combustibles
prior to leaving the secondary chamber.
B. Air Pollution
1. Much less particulate emissions into the
atmosphere by the installation of reasonable
maintenance-requiring equipment for remov-
al of particulates down to the 0. 1 micron size.
2. Continual quantitative monitoring of par-
ticulate concentration, size, and identifica-
tion.
3. Meteorological interlock for operation
and degree of control required.
4. The gaseous emission should be known,
i. e. , types and concentrations, and corre-
lated into the community inventory to insure
safety for public health respiration.
5. The particulate emission content should
be known, especially for such toxic metals
as lead, chromium, etc.
G Relative to Special Wastes
Special incinerator furnaces and appurten-
ances and controls with adequate knowledge
of pollutant effects for intractable wastes
from industry and demolition operations.
D. Relative to Economics
1. The first cost of a municipal incinerator
is too high. It should be reduced, perhaps
by simplifying the physical plant of building
and appurtenances.
2. Also, repairs and maintenance are too
high, especially in regard to the refractory
aspect and other high temperature materials
of construction, etc.
Hence, considerably more research and de-
sign is needed to have municipal incineration
fulfill the purpose and performance required
as a preferred refuse disposal method even
for the year of 1980, let alone the 21st century.
11
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DESIGN PARAMETERS FOR MUNICIPAL INCINERATORS
Herbert C. Johnson*
I INTRODUCTION
There are no nationally recognized design
standards for municipal incinerators. Much
has been published but only a few authors
have presented useable information on design.
By digesting most available information it
can be concluded that three basic designs are
presented. These can be divided as single
chamber, multiple chamber, and combination
designs.
Design parameters applicable to each of these
three designs will be covered after discussing
air pollution requirements, methods of
charging municipal incinerators, drying the
refuse, and the effects of air distribution.
Miscellaneous design parameters will be
briefed, followed by a closure on considera-
tions to minimize air pollution.
II PRINCIPLE OBJECTIVES OF MUNICIPAL
INCINERATORS
Any attempt to evaluate existing design
standards or to develop new standards
should be based on a thorough understanding
of all the objectives to be achieved. Basically
municipal incinerators have just one justifi-
cation to dispose of refuse at the lowest cost
in a manner satisfactory to the community
and to any surrounding communities. If other
satisfactory disposal methods can be found
that will show a lower total cost during the
period of time being planned for, the alterna-
tive disposal method should be selected.
Community satisfaction normally infers that
the appearance is not objectionable and air
pollution standards are complied with. Since
a municipal incinerator is expected to operate
at least 20 to 25 years, consideration should
be given to probable future regulations as
well as existing air pollution emission
allowances.
Future air Pollution requirements can be
expected to include:
A Visible Plume
Present - #2 Ringelmann maximum
allowable in most areas.
Future -
1 Dark smoke - ttl Ringelmann maximum
2 Equivalent opacity (light colored
plume) equivalent to #2 Ringelmann
maximum or less than #2 Ringelmann
number.
B Fallout - No detectable fly ash fallout
permitted now or in the future.
C Particulate
Present - 0. 85 lb/1000 Ib. gas at 12%
CO2 or 50% excess air in most areas,
some have reduced to 0. 6 or less.
Future - 0.5 lb/1000 Ib. or less.
D Gases - Not controlled at present in
most areas.
Future - Organic compounds restricted
to on the order of 100 PPM total carbon.
Carbon Monoxide - No limits at present.
Future - Restricted to 50 to 200 PPM.
Oxides of Nitrogen - Not controlled at
present. No controls likely in the fore-
seeable future.
Ill THE EFFECT OF DESIGN PARAMETERS
ON EMISSIONS
At the risk of some emissions and simplifi-
cations known design parameters and their
effects on the types of emissions outlined
are as follows:
*Senior Air Pollution Engineer, Bay Area Air Pollution
Control District, San Francisco, California, (prepared
February, 1966).
PA. C. ce. 20. 7. 66
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Design Parameters for Municipal Incinerators
A Dark Smoke - Primarily consists of small
carbon particles caused by incomplete
combustion; however, material causing
light colored plumes may be masked by
dark smoke.
General agreement that adequate time,
temperature, turbulence, and oxygen
should eliminate dark smoke.
B Fallout of Fly Ash
Large particles of fly ash usually are of
two types: (1) charred material (2) ash
particles containing essentially no com-
bustible. Charred material should not
escape if the three T's are adequate.
Some ash particles, because of their low
density, will become airborne. Gas
washers or mechanical collectors of
adequate efficiency will remove most ash
that might be noticeable downwind, as
well as any charred material not com-
pletely burned. Efficiency of settling
chambers is very low.
Particulate is generally defined as solid
material suspended in the flue gases.
Quantity of particulate is in terms of
weight per unit volume or weight of flue
gases. Correction factors are normally
applied to provide equal requirements
regardless of excess air.
If complete combustion is achieved, the
particulate emitted will consist of non-
conbustible material in the refuse. Part
of it may be simply blown from the fuel
bed, but a portion will be due to chemical
reactions in the fuel bed. When formed
by chemical reactions, the particle size
will be small, from sub-micron to 1 - 10
micron in size.
Mi.ch of the weight of particulate is
krrt:ater than 5 micron size, several types
of collecting devices will remove a sub-
stantial percentage of large particles.
Application of collection equipment to in-
cinerators requires a knowledge of the
problems. The hot gases must be cooled,
corrosion and erosion taken into consider-
ation. Adequate draft must be provided.
The quantity of particulate emission can
be substantially reduced by the design of
the incinerator, according to theory pub-
lished by the Los Angeles County Air
Pollution Control District and test data
corroborating their theory.
C Opacity
A light colored plume is discharged from
most municipal incinerators. Air pollu-
tion regulations of most large communities
now limit opacity since such emissions
contribute to reduced visibility. Los
Angeles County APCD engineers concluded
that this plume was caused by volatiliza-
tion and/or other chemical reactions in
the fuel bee). Their analysis showed
appreciable quantities of metallic salts
and oxides in microcrystalline form in
the stack effluent, which must have con-
densed after volatilization in the fuel bed.
Removal of these very small particles
from the flue gases would be expensive;
it has not been accomplished on a full-
scale municipal incinerator in this
country. However, substantial reduction
of opacity has been accomplished by de-
signs developed by engineers of the Los
Angeles APCD.
D Gases
Organic compounds and carbon monoxide
should be found only in very low concen-
trations in municipal incinerator effluent
if the three T's and 0- are adequate.
IV WASTE CHARGING METHODS
A Continuous
B Batch
C Repel., a<'(;
A Continuous charging is normally by means
of a chute feeding refuse onto a mechani-
cal grate or the refuse may be pushed
onto the grate by a hydraulic charger.
The crane operator's instructions are to
keep the chute filled with refuse to
-------
Design Parameters for Municipal Incinerators
provide more even temperatures and
better control of excess air than other
charging methods.
B Batch charging is defined as loading an
incinerator with a large quantity of refuse
at infrequent intervals, such as once per
hour or half hour.
Each batch is allowed to burn down until
just prior to the next charging, at which
time all or part of the ash and remaining
refuse is dumped into the ash pit. A
variation is to dump into the ash pit less
frequently, each new charge is dropped
on top of the remaining burning refuse.
The results achieved depend heavily on
the operators since the sequence of (-vents
can be selected as they see fit. Periods
of overfiring can result in excessive main-
tenance and emission of air contaminants.
Large quantities of cold air enter the
charging door during the charging period.
C Repetitive charging is intended to provide
relatively small charges at frequent in-
tervals. If continuous operating mechani-
cal grates are provided, each charge of
refuse can be placed on a bare grate area
rather than on top of previous charges.
Controls can be provided to open and close
the charging door quickly and to limit the
charging rate; lack of such controls allow
overcharging. Some types of inclined
grates which do not operate continuously
allow operators to adopt batch charging,
destroying the advantages of repetitive
charging.
V WASTE DRYING ZONE
Early incinerators needed some form of dry-
ing before the wet garbage could be burned.
Drying was done in several ways, such as
water tube grates to suspend the wet material
above a fire on a stationary grate below.
Preheated air was used in some installations.
Flame and heat gases from dried refuse
burning near the discharge end of mechanical
grates were returned above the wet fresh
charge for drying.
Today's refuse in this country averages
only 5 - 10% garbage, 30 to 40% total
moisture. Violent burning of dry material
almost immediately after charging may in-
dicate the need for a controlled ignition zone.
The countcrflow principle has been largely
replaced with parallel flow, which can be
utilized to provide flame and hot gases above
the rear grate sections where garbage and
other hard-to-burn material is aided in
final burn-out.
VI PRIMARY COMBUSTION ZONE
Variations in design make definitions by
zones difficult. Some present day municipal
incinerators contain only one chamber in
which all phases of combustion take place.
Regardless of design volatiles are driven
off rapidly in the first one-third to two-thirds
of the grate in rectangular furnaces. Fixed
carbon begins to burn almost immediately,
completes burning on rear sections of the
grate, or falls into the ash pit unburned.
VII INFLUENCE OF WASTE COMPOSITION
ON INCINERATOR DESIGN
The effect of the low moisture content of
today's refuse has been pointed out. Grates
30 to 40 feet long should allow practically
all fixed carbon, in most types of refuse, to
burn.
Exceptions may be large dense material such
as timber or logs which may only partially
burn during the time available on the grate.
The effects of non-combustible material are
significant. Dust and dirt will increase
particulate emission. The volatilization of
metallic salts, etc. , as previously described,
cause a light colored plume and are believed
to be responsible for slag formation which
damages refractory.
Metals, such as tin cans, apparently cause
no significant trouble. Bolts, screws, nails,
etc. can damage some types of grates.
Large pieces of metal can damage ash con-
veyors. High fuel bed temperatures can
-------
Design Parameters for Municipal Incinerators
melt glass, no difficulties have been re-
ported on mechanical grates. Glass has been
observed running through the stationary
grate of a large single chamber incinerator.
Most plastics burn satisfactorily but fillers
of clay, etc. undoubtedly increase particulate
and may, along with chlorides, contribute
to opacity.
Undoubtedly, there is a great deal known
about the effects of various mixtures of
materials which have not been reported and
more will be learned if particulate emissions
and effluent gases are analyzed.
VIII AIR SUPPLY
Probably the most important difference in
design parameters is the location and
quantity of air supplied in the first chamber
because:
A Burning rates are effected by air supply.
B Combustion rates in various portions of
the first chamber, as well as the need
for additional chambers, are effected
by air distribution and turbulence provided
in the first chamber.
C The biggest factor effecting emissions is
air distribution and turbulence.
D Arch height and volume of the first
chamber are related rather directly to
air distribution.
Keeping in mind that air distribution and
turbulence are the key factors in inciner-
ator design, the parameters developed to
fit the different theories advanced can be
explained as follows:
1 Single chamber theory
It has been proven that practically all
of the combustibles can be burned in
one large chamber if continuous or re-
petitive charging is provided at the
proper rates. Parameters found in the
literature^) are:
a At least 50% of the total air is
supplied as underfire air (through
the grates).
b Overfire air is supplied under
pressure through jets just above
the fuel bed.
c Burning rates per square foot of
grate of 60 or more Ib/ft^/hr are
achieved.
d A high arch provides a large com-
bustion volume, allowing sufficient
residence time to theoretically com-
plete combustion. The parameter
used is heat release (Btu/ft3/hr).
The heat release suggested should
not exceed 20, 000 Btu/ft3/hr, arch
heights are 12 to 18 feet.
e Mechanical grates 30 to 40 feet
long are suggested to obtain effec-
tive burn out. Grate width is
varied to provide desired capacity.
f Since particulate emission is very
high with this type of combustion,
settling chambers, mechanical
collectors, or scrubbers are
suggested.
A recent paper'9' recommends this
type of incinerator with a completely
water cooled interior, plus addi-
tional heat exchange surface to
lower exit temperature sufficiently
to allow installation of a high
efficiency collecting device. Re-
fractory maintenance is eliminated,
excess air is greatly reduced, and
large quantities of steam are
generated.
2 Multiple chamber theory*
Both small and large incinerators de-
signed to published standards^' ^» **)
have demonstrated low emissions of
particulate, and material causing
opacity. The parameters of this de-
sign are:
*See Table I and Figure 1 for multiple-chamber
retort incinerator and Figure 2 for multiple-
chamber In-Line incinerator.
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Design Parameters for Municipal Incinerators
Only 10 to 20% of the total air is
supplied as underfire air.
Sixty to seventy percent is supplied
as overfire air (through ports), 10 to
20% as secondary air in the second
chamber.
Burning rates per ft" of grate is
limited to 40 to -15 Ib/ft2/hr for
municipal size incinerators.
(5)
d Arch height is determined by a
formula developed by the authors
based on test data, etc. However,
a maximum average arch height of
8 feet has been recommended re-
gardless of chamber size. Heat
release is not specified, but if cal-
culated would be 20,000 Btu/ft3/hr
in the first chamber of municipal
size incinerators to under 15,000
Btu/ft^/hr if all combustion volume
is considered.
e A length/width ratio is developed
for grates, which does not appear
to be applicable to municipal incin-
erators. In private conversations
the authors have recommended that
length be limited to prevent exces-
sive horizontal velocity in the first
chamber. The width is selected to
provide the grate area required.
f Two secondary chambers are in-
cluded in this design. Sizing of
these chambers is by velocities as
shown in Table I.
g A gas washer was used to reduce
particulate on the one municipal
incinerator designed close to these
standards. An induced draft fan
produced the required draft.
Combination designs with rectangular
furnaces
Many municipal incinerators have been
designed in recent years that provide
more than one combustion chamber
but do not conform to the multiple
chamber design standards previously
cited. (2) While these units differ
considerably, the parameters used
generally are:
a High air flow through grates,
usually 50 to 80% of total air.
b Secondary air usually thru ports,
some jets may be included. Loca-
tions vary with designer.
c Burning rales of 50 to 70 lb/ft2 of
grate has become practically
standard.
d Arch height varies with designer,
usually 10 to 15 ft., which fixes
first chamber volume.
e Length/width ratio of grates varies.
The trend is to longer mechanical
grates which operate continuously.
f Secondary chamber designs vary.
A simple design consists of one
chamber with a gas washer built
into the exit end. More complex
are those including two combustion
chambers, a subsidence or settling
chamber, often followed by spray
chambers, gas washers or
scrubbers.
g Tall sU.cks are required in some
communities, others allow use of
induced draft and short stacks.
EX MISCELLANEOUS DESIGN PARAMETERS
A Auxiliary Fuel Burners
These burners have seldom been included
on municipal incinerators since contin-
uous or repetitive charging of today's
-------
PLAN VIEW
SIDE ELEVATION
I. STACK
2, SECONDARY AIR PORT
3. GAS BURNERS
4. ASH PIT CLEANOUT DOOR
5. GRATES
6. CHARGING DOOR
7. FLAME PORT
8. UNDERFIRE AIR PORT
9. IGNITION CHAMBER
10. OVERFIRE AIR PORT
M. MIXING CHAMBER
12. COMBUSTION CHAMBER
13. CLEANOUT DOOR
14. CURTAIN WALL PORT
h-H
END ELEVATION
SIZE OF INCINERATOR
POUNDS PER HOUR
50
100
150
250
500
750
1000
A
314
404
45
54
764
85*
94*
B
134
18
224
27
36
49i
54
c
22i
28 4
334
374
474
54
594
D
9
134
154
18
27
36
36
E
63
9
114
134
18
224
27
F
20*
27
29
36
494
54
584
G
134
18
224
27
36
45
45
H*
18
19
20
22
28
32
35
LENGTH IN INCHES
IJKLMNOPQRSTUVWXYZ
8
12
14
18
24
30
34
184
23
27
30
364
40
45
20
28
354
40
484
514
544
33
5
5
74
124
15
174
10
15
164
18
23
28
30
44
24
44
44
9
9
9
24
24
24
44
44
44
44
21
4
44
44
44
44
44
9
144
18
20
26
25
274
24
5
5
5
5
5
74
24
0
24
24
5
10
124
24
24
24
24
24
24
24
44
44
44
44
9
9
9
24
24
24
24
44
4*
44
44
44
44
44
9
9
9
44
44
44
44
9
9
9
Dimension "H" given in feet.
6
8
9
12
16
18
??
4
5
6
6
8
R
10
FIGURE 5. DESIGN STANDARDS FOR MULTIPLE-CHAMBER RETORT INCINERATORS
-------
[
"?&:"•"•
•
j
v\X-'-y^ •
I-•-! I-
PLAN VIEW
SIDE ELEVATION
1 . STACK
2. SECONDARY AIR PORTS
3. ASH PIT CLEANOUT DOORS
4. GRATES
5. CHARGING DOOR
6. FLAME PORT
7. IGNITION CHAMBER
8. OVERFIRE AIR PORTS
9. MIXING CHAMBER
10. COMBUSTION CHAMBER
1 i. CLEANOUT DOORS
12. UNDERFIRE AIR PORTS
13. CURTAIN WALL PORT
14. DAMPER
15. GAS BURNERS
INERATOR
R HOUR
(J UJ
Z Q.
(/)
u, o
0 Z
UJ O
N Q.
V)
750
1000
1500
2000
A
85i
94*
99
108
B
494
54
76i
90
C
515
54
65
69i
D
45
47i
55
57 i
LENGTH IN INCHES
EFGH 1 JK|_*MNOPQRSTUVWX Y
152
18
18
221
54
63
72
79i
27
314
36
40i
27
314
36
40i
9*
11
124
15
24
29
32
36
18
22i
27
31i
32
35
38
40
4i
4i
4i
44
5
5
5
5
74
10
74
10
9
9
9
9
24
24
44
44
*Di mansion "L" given in feet.
?4
24
44
44
10
30
30
30
9
9
9
9
44
44
44
44
5
7
A
9
11
12
14
15
51
5?
614
634
7
8
9
10
FIGURE 6. DESIGN STANDSRDS FOR MULTIPLE-CHAMBER IN-LINE INCINERATORS
-------
TABLE I
MULTIPLE-CHAMBER INCINERATOR DESIGN FACTORS
ITEM AND SYMBOL
RECOMMENDED VALUE
ALLOWABLE
DEVIATION
A. Primary Combust i on Zone;
1, . Grate load ing , LG
2. Grate area. AG
3. Average arch height. HA
4. Length to width ratio (approx.):
a. Retort
b. In- 1 ine
10 Log Rc;Ibs/hr-ft2 where Rc equals the refuse combustion rate in Ibs/hr (refer to Fig.3)
Rc + LG: ft2
4/3\bout 0.7 of mixing chambe r velocity
5 to 6 ft/sec' always l^ss than 10 ft/sec
Average a rch he i ght, ft
Range - 1.3:1 to 1.5:1
Fixed by gas velocities due to constant incinerator width
20*
2056
1 20*
C. Combustion Air:
1. Air requirement batch charging operation
2. Combust ion air distribution:
a. Overfi re air ports
b. Underfire oir ports
c. Mi x ing chamber air ports
3. Port siting, nominal inlet velocity pressure
4. Air inlet ports oversize factors:
a . Pr irea ry air inlet
b. Under fire air inlet
c. Secondary air inlet
D. Furnace Temperature:
Average temperature, combust ion products
E . Auxi HJI ry Bu rne rs :
Norma 1 duty requirements:
1. Primary burner
2. Secondary burner
F. Draft Requirements:
1. Theoretical stack droft. Dj
2. Available primary air induction draft. D^. (Assume equivalent to inlet
veloci ty pressure. )
3. Natural draft stack velocity, Vg
Basis: 300/6 excess oir. 50?t air requirement admitted through adjustable ports; 50% air
requirement met by open charge door and leakage
lf)% of total air required
\0% of total air required
20^ of total air required
0.] inch water gage
1.5 for over 500 Ibs/hr to 2.5 for 50 Ibs/hr
2.0 for over 500 Ibs/hr to 5.0 for 50 Ibs/hr
1000°F
i 20°F
2500-5000
Btu per Ib of moisture in ihe refuse
0.2-0.35 inch water sage
0.1-0.2 inch wntcr gage
Less than 30 ft/sec & 900°F
-------
Design Parameters for 1.1. A. Incinerator Classes
REFERENCES
1 Rose, A. H. Stenburg, R. L., Corn, M. ,
Horsley, R. R.. Allen, D. R.. and
Kolp, P.W. Air Pollution Effects of
Incinerator Firing Practices and Com-
bustion Air Distribution. JAPCA, 8,
297-306. February 1959.
2 Stenburg, R. L., Horsley, R. R. , Herrick,
R. A. , and Rose, A. H. Effects of
Fuel Moisture and Incinerator Design
on Effluents from Incinerators. Proc.
52nd Annual Meeting APCA, Los
Angeles, California. June 1959.
3 Stenburg, R. L., Hangebrauck, R. P. ,
von Lehmden, D. J., and Rose, A.H.
Effect of High Volatile Fuel on Incin-
erator Effluents. JAPCA, 11, 376-83.
August 1961.
4 Stenburg, R. L., Hangebrauck, R. P.,
von Lehmden, D. J. , and Rose, A.H.
Field Evaluation of Combustion Air
Effects on Atmospheric Emissions
from Municipal Incinerators. JAPCA
12, 83-89. February 1962.
ADDENDUM: (Note: Enclosed is a Quick
Check Chart for incinerator
design used by Joseph Coder
Incinerators)
The purpose of the following chart is to pro-
vide a convenient way of checking our own
and our competitors'incinerators when
drawings or specifications are available to
see if the units meet the 1.1. A. Standards.
This chart will enable "on-the-spot" check
at the architect's or engineer's office. Data
not listed on this chart may be determined by
interpolation. As a specific example, if
capacity is 150 Ibs 'per hour of Type 1 Waste,
the burning rate would be determined by
adding 26 and 30 in the burning rate column,
dividing by two, and coming out with a fac-
tor of 28.
BURNING RATE: This is the amount of
refuse that can be consumed on each square
foot of grate area in each hour. It is
figured by dividing the capacity in pounds
per hour by the grate area in square feet.
GRATE AREA: As can be seen above, grate
area is determined by dividing the capacity
by the burning rate and is measured in a
horizontal plane as can be seen in the
sketch by dimensions (a) and (b). Grate
area for Type 1 Waste can include some
hearth but must not exceed 20% of total
burning area. Hearth area for Type 2
Waste can consist of 50% of the total burn-
ing area. When burning Type 3 Waste, the
grate area must not exceed 35% of the total
burning area. Where step grates are used
in lieu of hearth, they shall occupy at least
65% of the burning area surface.
TOTAL INCINERATOR VOLUME: Total
interior incinerator volume is exclusive
of the volume below the grates or hearth.
MIN. AREA IN HI-VELOCITY PASS: Mini-
mun area in the hi-velocity pass as shown
in the sketch is measured in a horizontal
plane although this minimum area should
be checked throughout the gas travel of the
Incinerator as no cross-sectional are inside
of the unit through which the gases pass
should be less than this area. This minimum
area is based on a velocity of 35 feet per
second at 1400°F.
GAS TRAVEL: The gas travel is a measure
of the distance the gases travel in a hori-
zontal plane in the low-velocity pass and in
the case of this sketch, it is the distance
between the center line of the two chambers
in the secondary combustion chamber of the
incinerator. This distance is figured by
taking the square root of the minimum area
in the low-velocity pass.
Other physical factors must be considered
when checking 1.1. A. Standards such as
wall construction, breeching size and con-
struction, chimney size, and the amount of
auxiliary fuel required. The most important
construction feature we mention here:
-------
Design Parameters for Municipal Incinerators
Adequate control of participate and opacity
will require a reassessment of municipal
incinerator design. The Los Angeles design
principles offer a possible solution; effective-
ness in controlling emissions and costs
remain uncertain. Opacity of the plume
from all other designs in this country can be
expected to be excessive since high fuel bed
temperatures will volatilize metallic salts
or oxides. If collection devices capable of
removing particles in the sub-micron size
range are to be considered, water cooled
furnaces operating with minimum excess
air may be the most economical solution.
Other approaches are possible such as
partial water cooling in areas where main-
tenance is high, using the steam generated
to power induced draft fans; Venturi
scrubbers operating at 30 to 50" H2O pres-
sure drop being used to control particulate
and opacity.
When one considers the cost of such alter-
natives, increasing the grate area by some
50% as per Los Angeles theory appears to
be well worth further investigation.
REFERENCES
1 Anon., 1.1. A. Incinerator Standards,
Incinerator Institute of America, 420
Lexington Avenue. New York 17, New
York.
2 Williamson, J. E. et. al. Design
Standards for Multiple Chamber In-
cinerators - Part I, Indus. Water and
Wastes, pp. 61-65, May-June, 1961.
3 Williamson, J. E. et. al. Design
Standards for Multiple Chamber In-
cinerators - Part II, Indus. Water
and Wastes, pp. 97-101, July-August,
19G1.
4 Grceley, S. A. et. al. Incinerator De-
sign and the Fly-Ash Problem - Part
II, The American City, pp. 112-114.
June. 1955.
5 Rose, A.H. et. al Incinerator Design
standards: Research Findings,
LAAPCD, Publication No. 60.
6 Voelker, E. M. The Problems of Apply-
ing Incinerator Criteria, JAPCA,
Vol. 14, No. 9, pp. 363-366, 377,
Sept.. 1964.
7 Anon. , Proceedings of 1964 National In-
cinerator Conference, ASME, 345 E.
47th Street, New York 17, New York.
8 Meissner, H. G. Designing A Modern
Incinerator, Power, April, 1958, pp.
80-83.
9 Flood, L.P. Air Pollution from Incin-
erators -- Causes & Cures, Civil
Engineering, ASCE, December, 1965,
44 pp.
10
-------
MUNICIPAL INCINERATION:
GOOD OPERATING PRACTICES
Leonard C. Mandell, P. E.
I Introduction
The aim of present-day, municipal inciner-
ation is to convert and reduce small size
(under 2 feet in length) combustible refuse,
mainly cellulose material and garbage, into
inert ashes and oxidized gases. Hence, good
operating procedures should be established
to attain and maintain the best performance
with the plant's capability. Once estab-
lished, a program of enforcement by insp-
ection, coupled with education and supervision
of the personnel should be followed.
II Desirable Operating Objectives
A. In this regard, the following objectives
are desirable:
1. Operate (a) with a sensible minimum of
labor, power and accessory costs, (b) with
a minimum of political featherbedding and re-
lated incompetent personnel, (c) with a min-
imum of inefficient, shift schedules and gold-
braiding of equipment and controls.
.Uneconomical waste-heat recovery and priv-
ileged, high-cost contractors are typical of
additional wasteful expenditures.
2. Operate with a minimum of break-downs,
repairs, and downtime, by hiring potentially
capable people and training them in operating
and maintenance procedures. A program of
planned-maintenance with an adequate inven-
tory of spare parts and well-equipped shops
is necessary.
3. Operate with a minimum of air polluting
emissions. This means that particulate con-
trol equipment should be incorporated to re-
move all solid and liquid aerosols above
approximately 0.4 micron in diameter. This
is an arrestance efficiency of approximately
98% by weight. Further, the combustion
process itself should produce only complete-
ly oxidized gases of carbon, hydrogen sulfur,
and nitrogen.
4. Operate with a minimum of unburnt organ-
ic matter in the residue. This should amount
to approximately 2% - 3% by weight for com-
bustible refuse and approximately 7% - 9% by
weight for mixed refuse. This is controllable
by feed and over and underfire air rates,
effectiveness of turbulence, and further
temperatures.
B. Conversely Operate with a Maximum of:
!• Operational continuity, performance, and
reliability. This is best assured by securing
well-trained, operating and maintenance per-
sonnel, the use of properly designed and
maintained equipment and controls, and a
planned program for their implementation and
coordination.
2. Operate wich maximum worker and process
efficiencies. These requisites require con-
tinual effort by responsible individuals
because of the inherent susceptibility to
political interference and influence. Both
should be kept to a minimum. It may be
pointed out that too many times "the
minimum" turns out to be the maximum. Hence,
while influence may be tolerable, inter-
ference is unacceptable. A program of Job
education, good organization rapport, and
better than adequate pay and fringe benefits
(sick leave, Blue Cross, Blue Shield, and
vacation pay) is important. Further,
adequate maintenance of the operating equip-
ment and instrumentation is essential.
3. Operate with a maximum of "mass refuse
reduction." For combustible refuse this
amounts to 95% - 97% by volume, and 95% by
weight. For mixed refuse this amounts to
approximately 90% by volume, approximately
85% by weight. (Note: Due to Eefuse varia-
tions, approximate values are expressed.)
PA.C.ce.46.5.70
-------
Municipal Incineration: Good Operating Practices
C. Further-Operate with
a Reasonable Degree of:
1. Safe, satisfactory working conditions for
the employees. This implies adequate vent-
ilation over the pits, the charging hoppers,
and the operating floors. Good lighting; good
housekeeping; cleanliness; safe walk-ways;
handrails, especially around'the charging
wells or pits; washroom facilities; and a
planned course of action for emergencies be-
yond the limits of applied first-aid should be
established. The availability and use of safe-
ty belts and chains, the availability and use
of safety goggles, gloves, non-slip hard-top
shoes and also the availability of ready-to-
use fire fighting equipment are all necessary
safety requisites. Further, conspicuously
mounted safety posters showing rules and
good practices are also helpful. It should be
noted that sincere, well-trained personnel
are important. Their employment is manda-
tory for good operation. In addition, a sound,
reasonable safety budget should not only be
established, but maintained and expended
year after year.
One effective way of attaining these operation-
al goals is by a planned, thorough, yearly
inspection of the Incinerator Facility from the
personnel right down through the entire plant.
Information obtained from this inspection
should be recorded accurately, and evalua-
tion for appropriate action should follow. The
recorded information together with the actions
taken should be placed on file for future ref-
erence.
II Operating Practices.
Successful incineration operation begins with
the entrance of trucks and autos onto the prop-
erty. An overall, organized plan starting with
the weighing of the incoming-refuse, to the
weighing of the outgoing-ash, and monitoring
of gaseous effluents should be in effect for
every hour of the day throughout the year.
Effective controls should also be established
for any liquid effluent prior to discharge. It
should be noted that it is important to have
rules and regulations for the collection crews
and the citizenry to prevent the serious oper-
ational problems that may result from the
entrance of explosive, oversize, and/or very
wet, intractable wastes into the storage pit.
Finally, the importance of sincere, well-
trained personnel cannot be over-emphasized.
Hence, minimum placement or civil service
examinations and status are highly desirable
practices.
A. Duties of the Raw Refuse
Handling Operator
All incoming refuse should be weighed,
described, and its source recorded. Only
small size combustible and mixed refuse
should be allowed to enter the furnace. This
control may be effected by four different op-
erators, scale-master, dump floor pit atten-
dant, crane operator, and charging floor
attendant. Their duties are:
1. Scale-master: (a) to maintain a simple
system of records of net weights, refuse des-
cription, time, date, and origin, (b) to check
on licenses and collect tariffs that may be re-
quired, (c) to keep all undesirable materials
from entering area.
2. Dump Floor Attendant: (a) to watch for
and reject all liquids, large and dangerous
items, and restricted or undesirable mater-
ials from entering the pits, (b) to watch for
and sound alarm in the event of pit fires, (c)
to direct all wet loads into a special section
of the pit. (d) to be able to "double" as a
crane operator, (e) toprevent congestion in
the dumping area by proper traffic control
and to discourage loitering by haulers.
3. Crane Operator: (a) should load proper
type refuse into hoppers; dry, wet, or mix-
tures as required, and to help maintain de-
sirable burning zone temperatures, (b) should
manage the pit in such a manner that dry re-
fuse is in the pit to bring units up to temperature
for start-ups, (c) to watch for fires, clean
them out, and drop burning, smoldering re-
fuse into charging hoppers. It is his duty to
keep the hoppers constantly full, especially
where full hoppers serve as air seals.
4. Charging Floor Attendant: (a) to keep over-
size and undesirable refuse from entering
the furnace, (b) to watch for the entry of ex-
plosives. If one is sighted, he should stop the
charging-stoker, call the foreman, and clear
the area quickly. It is the foreman's respon-
sibility to arrange for the safe removal of
this danger, (c) to watch for fire in hopper
and report immediately, so that corrective
-------
Municipal Incineration: Good Operating Practices
action can be taken, to operate the ventilating
exhaust fans in order to remove smoke and
other eye-tearing and smarting gases from
work area, (e) to be able to "double" as the
crane operator and as a fireman.
B. The Furnace/Operators Duties
1. Firemen: Their responsibility is to main-
tain good burn-out and efficient combustion
in proportion to the load-demands of power-
steam, if applicable, and/or pit accumula-
tions. Their duties are: (a) to keep the
furnaces clean and free of clogging, (b) check
on and operate over-fire/under-fire air dam-
pers, (c) check and maintain adequate draft
(. 04-. 08") in ignition chamber, (d) to see
that over-fire air starts above the 1100°F.
flue gas temperature. This helps to burn fly-
ash, (e) control drying-stokers speeds (30-
50 ft/hour) of continuous feed design, (f) con-
trol burning stoker speeds (25-70 ft/hour) of
continuous feed design, (g) to avoid running
the burning stoker at greater speed than the
drying-stoker s.s this results in poor burn-
out and more smoke. A 60 ft/min. burning
stoker speed is normal, (h) control the charg-
ing and fire dumping of batch charging type
furnaces, (i) to keep ambient furnace temp-
eratures below 1800°F. because grates and
brickwork can be damaged above 1800°F.
(j) admit secondary air as needed for cooling
of gases to protect the furnace/incinerator
and chimney structures.
2. Ash Conveyor Attendant/Truckman: (a) to
keep the water in the ash-chute to overflow
level at all times in order to maintain a
draft-seal, (b) to keep the conveyors moving
during firing, making sure that they do not
become clogged, (c) in installations that do
not have conveyor systems, the attendant
keeps the dump chute cleared, (d) clean his
equipment as often as once every 24 hours if
required to prevent build-up of intractable
material that can clog conveyor, and also pre-
vent odors from developing, (e) lubricate
bearings, sprockets, and chains as often as
once per shift if required to prevent abrasion
and wear to minimize break-downs.
Ill Maintenance and Repair Practice
A planned program of preventative mainte-
nance with an adequate inventory of spare
parts in conjunction with suitably equipped
facilities constitutes good practice. A min-
imum of down-time due to breakdown and
repairs can be attained by employing capable
personnel who are properly trained in the op-
erations and maintenance procedures related
to the equipment by following these recom-
mendations: (1) expend annually at least 5%
of total capital plant cost for maintenance and
repair. (2) expend at least 10-15% of operat-
ing cost: 50% for labor and 50% for materials.
(3) conduct weekly inspections, cleaning and
housekeeping, lubrication, clinker and slag
removal, and minor preventative repairs.
(4) plan thoroughly for all major repairs.
(Note: Major modernization seems to be need-
ed approximately every 15 years. ) (5) main-
tain a good stock of firebricks, insulating
bricks, grate components, motors, chain
parts and other frequently replaced accesso-
ries and parts. (6) operate an up-to-date
machine shop, electric shop, and welding
shop staffed with master mechanics capable
of performing the work. (7) maintain up-to-
date personnel training programs. The
foreman should report all defective parts and
faulty mechanisms on his daily report to the
superintendent. Proper repairs must be sche-
duled immediately. (8) maintain lubrication
schedules as recommended by the manufac-
turer of the respective equipment, use lub-
ricants approved by a recognized petroleum
company. (9) maintain a high standard of
plant cleanliness inside and outside as this
is indicative of good overall plant operation.
Clean up the outside grounds at least once a
week. (10) provide periodic cleaning of all
flues and chambers. (11) careful attention
should be given to inspection and mainten-
ance of air pollution control equipment.
(12) the stack should be inspected at least
every other year to locate loose and cracked
bricks, corroded or loose bolt fastenings or
outside bands and to determine the need for
maintenance. (13) maintain a system of re-
cords, in the incinerator office, showing the
cost, exactly what was done, when, why and
by whom.
-------
Municipal Incineration: Good Operating Practices
IV Air Pollution Control - Good Operating
Practices
A. An Ideal Process and Its Variables
From a purely theoretical standpoint, perfect
air pollution control applied to municipal
incineration would emit an effluent with the
following characteristics: (1) "a suspended
particulate concentration equal to that in the
air used for combustion. " (2) a gas-mixture
composition of nitrogen, oxygen, water vapor,
and argon; also, carbon dioxide, methane,
hydrogen, ozone, and the rare gases at the
combustion-air concentrations.
With this plane of reference, it can be said
that the average concentration of particulates,
carbon dioxide, or any other gases except
water vapor greater than the respective
combustion-air concentration departs from
the perfect condition. This degree of depart-
ure can be said to be a measure of the eff-
luent's air pollution potential. Its classifi-
cation as an air pollutant depends upon:
(1) the quality of the combustion-air. (2) the
local meteorology at the time of release into
the atmosphere. (3) the local topography
within the zone of significance of the atmos-
pheric plume. (4) the population density and
composition within this zone of significance.
(5) the land use and activities within this
zone of significance.
These seven parameters involve a dynamic,
ecological relationship between the effluent,
the immediate physical environment of land,
water, and air. The acceptability of this
relationship, from a Public Health and Wel-
fare standpoint, is governed by the finite,
self-cleansing ability of the environment to
maintain concentrations below harmful thres-
holds.
From a practical standpoint, good practice
calls for cessation of incinerator operation
during critical periods of adverse meteorology.
This implies that an alternate stand-by means
qf disposal be available during these critical
periods. Controlling the quality of the com-
bustion air, at present, presents no apparent
advantage while the other items of topography,
population, and land use is beyond the control
of Incinerator Management.
B. Available Control Methods
1. In General. Good operating practice is in
reality limited by the design of the incinera-
tor facility. However, there are at least
five opportunities for Air Pollution Control
of which only one or more may be available
in any plant. The degree of control will in-
crease in proportion to the utilization of
these opportunities: (a) pre-treatment of the
refuse, (b) proper charging and feeding (c)
good combustion efficiency, (d) effective air
pollution control equipment, (e) adequate
control instrumentation.
It should be noted that until six years or so
ago, air pollution control equipment was not
incorporated and designed into the conven-
tional incinerator plant. Whatever control
that was available consisted of attempts to
burn the refuse without visible smoke. This
was done by manual operation of grate speeds,
mixing the refuse, feed rate, combustion air
supply, and by incidental arrestance of ash
and slag by wasteheat boiler-tubes, and other
flue-gas type obstructions. Settling chambers,
so-called, were provided for the relatively
large size fly and char particles, greater
than several hundred microns, which cause
a soiling nuisance within 10-15 stack diam-
eters of the emission point.
Typical effluents with little or no control,
from 1945-1960 design incinerators, would
contain the following pertinent pollutants:
(a) suspended particulates, (smoke, soot,
grit, dust, fume, fly-ash) in the plume of
3.5-5.0 lbs/1000 Ibs. of gas (corrected to
50% excess air) with a mass median diameter
of 30-50 microns and a count median just be-
low 0.1 microns. By count.each pound of re-
fuse when burned should give approximately
10 . particles of which 96% were greater
than .01 and less than 0.1 micron in size.
(b) component gases as sulfur oxides (SC>2),
0.2 - 1.3 ppm; nitrogen oxides (NO2>, 0.2-1.5;
carbon monoxide, 30-1000 ppm; carbon diox-
ide, 1-4% by volume and oxidizable sulfur
compounds 2-8 ppm.
2. Pre-treatment of the Refuse. Wherever
feasible, all refuse should be opened, size-
reduced, and sorted-free of bottles, cans,
and other intractable type wastes. Light, wa-
ter spraying of everyday refuse will'also help
-------
Municipal Incineration: Good Operating Practices
in preventing pre-ignition of the refuse in the
charging hopper.
A recommended practice, not sufficiently in
vogue, is to provide an effective sorting line
and power disintegration of the refuse to
obtain pieces in the 1 inch size instead of
chunks of pieces in the 12 to 36 inch size.
This tends to provide a more homogeneous
refuse fuel that will burn easier and more
efficiently, and be more adaptable to control
influence--all of which will tend to reduce air
pollution emissions.
3. Charging and Feeding Into the Furnace.
(a) batch charging, at best, still creates ex-
cessive amounts of smoke and fly-ash due to
the uncontrolled disturbance of the bed. Pro-
per cycling and dumping of the grates with
full-overhead hoppers constitutes good prac-
tice. Excessive entrance of refuse (overload-
ing) also causes poor burn-out of the organic
matter, (b) continuous feeding via a transfer
of drying-grate with a full hopper (to act as a
semi-gas seal) tends to maintain a relatively
stable, overfire-draft. The transfer of feed-
grate speed should be maintained slightly
higher than .the main stoker speed (this controls
the depth of the fuel bed) to obtain good burn-
out efficiency.
4. Combustion Efficiency, (a) the nature of
flame combustion: the nature of the actual in-
cineration process tends towards the proba-
bility of incomplete or inefficient oxidation
with the generation of large amounts of smoke
and pollutants. Good combustion requires
continued watchfulness and related control
responses to provide adequate air to fuel rat-
ios in intimate dynamic timed-contact with
the volatile and/or fixed carbon molecules.
(Note: This presents an opportunity for "sin-
cere, well-trained personnel" to show their
worth.
Today's refuse contains a high percentage of
volatile matter, and less than 20% fixed car-
bon, with the former burning above the fuel
bed. Experience has shown that combustion
occurs in three definite but overlapping and
dependent phases: (1) evaporation of moisture
(an endothermic phase) less than 212°F. (2)
distillation of the volatile hydrocarbon (tar,
oils, waxes, resins, etc. ) that come off be-
tween 300-800° F. ( an exothermic phase).
(3) straightforward combustion of the re-
maining fixed carbon at 1100-1250° F. (an
exothermic phase).
Stoichiometric combustion of conventional
1967 refuse creates furnace temperatures in
excess of 3200 F. This is much too high
for satisfactory refractory life and other
materials of construction. Hence, provisions
for cooling the gases and furnace-proper by
excess air amounts up to 300% and/or water
cooled walls (that bring excess air down to
50-70% level) must be available, (b) furnace
operation: air pollution control starts in the
furnace. Tests have shown that: (1) fly ash
carry over is proportional to (Furnace Veloc-
ity)^ (Furnace Size), (Heat Release), (2)
flame temperatures are approximately 200-
400 F. greater than wall temperatures, (3)
the more effective the over-fire air, the
smaller the fly ash carry over, (4) too much
excess air cools gases before completion of
combustion with smoke formation, (5) the
more forced, under-fire air, the more fly
ash.
Hence, the proper control of grate speeds,
over-fire, and below grate air supplied to-
gether with induced secondary air must all
be continually and carefully controlled by
the operator.
The fuel bed depth should be controlled to
provide a complete burn-out by the time the
ash reaches the dump-line. This is pro-
portional to stoker speeds, and over-fire and
under-fire air rates and points of application.
Efforts should be made to prevent large varia-
tions in temperature. This causes thermal
shocks, spalling, expansion, and contraction
breakage of the refractory materials.
Shift .operating schedules disclosed by a
recent survey showed that 36% of plants op-
erate eight hours per day, 53% operate
twenty-four hours per day, and 6% operate
sixteen hours per day.
5. Air Pollution Control Equipment
Air pollution control equipment is just be-
ginning to be designed as an integral part
of the incinerator plant. As previously men-
tioned, until I960 or so, subsidence or set-
tling chambers and water sprays character-
ized the American design, their efficiencies
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Municipal Incineration: Good Operating Practices
for suspended particulates were approximately
10 and';-20% respectively.
A recent survey of shift operating schedules
s-howed that the application of wet-baffles and
multi-clones have increased the collection
efficiency to 60-70%. It is the writer's.
opinion that the next 5-10 years will see the
appearance of electrostatic precipitators
with efficiencies in the 95% and higher range.
It should be noted that high pressure-drop
venturi scrubbers can give efficiencies in the
97% range and bag collectors to greater than
99% for particulates down to the 0. 1 micron
6. Instrumentation. The existence of ade-
quate instrumentation in the overage plant
is lacking. The indication of draft and
several gas temperatures in the furnace and
flue-gas system are conventional. -'In addition
the following would assist in air pollution con-
trol: (a) stoker speed indication, (b) CFM/
jet for overfire air with total furnace indica-
tion, (c) CFM/jet under-fire air with total
furnace indication, (d) a continual indication
of unburnt material in residue coming off the
grate, (e) an indication or record of smoke
concentration entering the stack, (f) a meas-
ure of the particulate concentration entering
the stack, (g) meteorological instrumentation:
wind, speed, relative humidity, and wind di-
rection, (h) a stack mirror to allow the op-
erators to view the plume discharge, (i)
good audio and visual communications, speak-
ers, telephones, closed circuit TV to view
the combustion chamber, ash drop area,
stack, etc.
7. Comments Pertaining to Many of the
Present Plants:
(a) on the negative side: there really isn't
much that can be done: (1) because air pol-
lution control equipment does not exist. (2)
because of inadequate instrumentation. (3)
because the quantity of refuse to be burned is
much greater than the ability of the furnace to
burn it efficiently. (4) because of under-
trained, under-staffed, under-activated per-
sonnel, (b) the positive side: (1) schedule
the burning rates in proportion to daily accum-
ulation and storage capacity, in order to keep
below or to a minimum the degree of exceed-
ing the design rating of the plant. (2) main-
tain the furnace, ancillary equipment and
auxiliaries in good condition. (3) maintain a
high degree of worker morale. This encour-
ages concern and proper attitude necessary
for good operation. (4) have dust-arrestance
equipment installed. (5) investigate better or
more instrumentation for a running guide to
the operators. (6) have at least a CO? and
optical smoke records kept during all opera-
tions. (7) have a sufficient number of obser-
vation ports to ensure good visual inspections.
(8) keep furnace and flue passages clean.
V. Conclusion
I would like to close with these few thoughts:
A. An incinerator should be operated for
incineration purposes only, not as a heat
source for steam generation unless proper
provisions of auxiliary fuel and air pollution
control are incorporated therein.
B. Operate the incinerator as a business
with strict rules and regulations. It should
be kept in mind that incineration is a part of
the disposal concept, and is accordingly sus-
ceptible to a high degree of apathetic thinking.
C. It is becoming generally accepted that
clean air is as important to health as clean
water. In this regard, sewage treatment to-
gether with the natural cleansing forces of
time, sun, and aeration are provided for
liquid wastes. Further, all water is treated
again at the Potable Treatment plants. Hence,
at least two efforts and most of the time three
treatments are made to control water pollu-
tion and purity. In incineration, however,
once the flue gases enter the atmosphere,
there is no equivalent air treatment plant to
clean the air before it is breathed. Hence,
it appears advisable and even mandatory to
incorporate both the equivalent of waste treat-
ment and air treatment in the incinerator of
the future.
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GOOD OPERATION PRACTICES FOR
MUNICIPAL INCINERATORS
Herbert C. Johnson*
Operating procedures for municipal incinera-
tors vary considerably for different designs.
The ideal design would minimize the influence
of the operator on performance; his responsi-
bility would be limited to keeping a hopper or
chute filled with refuse, and removing ash.
Most incinerators require considerable judg-
ment to be exercised by the operator. Ex-
cessive air pollution, high maintenance and
breakdowns often are the fault of the
operators.
Good operation requires consideration of the
following factors:
I CHARGING SCHEDULE
Rectangular furnaces with mechanical grates
are usually designed for continuous or repe-
titive charging. The chute should be kept
full of refuse at all times if a continuous
charge system is provided.
Repetitive charging means that a charge is
added frequently and at regular intervals
through each charging door in sequence. The
stokers are operated at frequent intervals
to keep the refuse moving toward the discharge
end. (Some stokers operate continuously,
requiring periodic speed adjustment.) Refuse
is usually charged into the incinerator at
2- to 5-minute intervals, depending on the
size of crane bucket, number of charging
doors, number of incinerators, and capacity
of incinerators.
Batch charging is applicable only to certain
types of incinerators such as round furnaces
equipped with rotary grates. Manufacturer's
recommendations should be followed unless
tests prove other procedures reduce
emissions, increase burning rate, or reduce
maintenance. If the periodic burndown
method is used, the procedure is (1) dump
grates and clean fire (2) charge the prescribed
amount of refuse, and (3) close charging
door and allow refuse to burn nearly to com-
pletion. Repeat these three steps.
II PROPER FUEL BED DEPTH
The depth of refuse at the charging end of
the furnace usually is, or should be, deter-
mined by design features of the charging
system and crane bucket size (excluding
batch charging). Depth should decrease
toward the ash pit end so that only a relatively
thin layer of ash covers the end of the grate.
The operator can vary air flow thru the
grates and grate speed, usually within a
narrow range.
A Continuous feed systems are designed to
provide a fixed depth of refuse at the
charging end. The operator can vary air
flow thru the grate and grate speed. Both
should be adjusted to completely burn the
refuse by the time it reaches the end of
the grate. Emissions can usually be
reduced by reducing both grate speed and
underfire air, which also reduces burning
rate.
B Repetitive charging systems are intended
to be operated so that refuse is charged
on the grate after the previous charge has
moved beyond the charging area. Initial
depth will depend on the size of the crane
bucket, should not be more than 3 to 4 feet
deep. Minimum depth and less underfire
air should reduce emissions. Grate
speed must be adjusted to provide, com-
plete burnout on the grate.
C Batch Charge
Depth of fuel bed should follow manufac-
turer's instructions.
Ill NORMAL TEMPERATURES
First chamber gas temperature normally
recommended is 1600°F. Flame tempera-
tures in some regions may be much higher
and may cause fictitious thermocouple
readings.
*Senior Air Pollution Engineer, Bay Area Air Pollution Control District, San Francisco, Calif-
ornia, (prepared February, 1966).
PA.C.ce. 21. 7. 66 1
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Good Operating Practices for Municipal Incinerators
Secondary chamber gas temperatures should
be only slightly lower in large incinerators
and should be closer to actual gas tempera-
tures than first chamber readings; 1400° to
1500°F should be satisfactory.
Stack temperature will be above 1000°F un-
less barometric dampers or water sprays
are installed. Operators should be informed
of design temperature range for stack.
IV EXCESS AIR - has two purposes: 1) to
assure adequate oxygen for combustion, and
2) to control temperatures.
Today's refuse contains much more heat than
necessary to maintain 1600°F if only the
theoretical amount of air is supplied. There-
fore, from 100 to 200% excess air must be
supplied to cool the combustion products;
temperature determines the amount of excess
air supplied.
V COMBUSTION AIR DISTRIBUTION
A Underfire to overfire air ratio. Consider-
able controversy exists on this ratio,
varying from 2 to 1 to 1 to 7. A 1 to 1
ratio is being used at present by many
designers. Most operators tend to use
too much underfire air, which increases
air pollution. However, many incinerators
will operate at their designed ratings only
by supplying a high percentage of underfire
air.
B
Secondary combustion air is not provided
for in most municipal incinerators. This
is a feature of the Los Angeles design
which should be further evaluated.
VI NORMAL STOKING PROCEDURE
The main purpose of mechanical grates is
supposed to be to reduce the labor of hand
stoking. Proper operation of mechanical
grates (stokers), correct fuel bed depth,
underfire air adjustment, and burning rate
should eliminate most hand stoking.
VII NORMAL AIR PRESSURE IN
COMBUSTION CHAMBERS
A negative pressure should always be main-
tained in all combustion chambers. A
positive pressure will cause gas and flames
to escape through overfire air ports,
charging doors when opened, and any cracks
that develop in the chamber lining. These
conditions are dangerous to personnel,
damage the chamber walls and arch, and
may prevent the flow of adequate overfire
air. Positive pressure is caused by 1)
failure of draft system 2) supplying too much
air under pressure to the furnace (underfire
or overfire air) 3) too high a burning rate
4) failure to close charging doors promptly,
and 5) leaving inspection or stoking doors
open.
VIII INFLUENCE OF DILUTION AIR
ON POLLUTION FORMATION
This was discussed under IV and V.
Obviously, no more air should be introduced
than necessary for complete combustion and
temperature control. Only sufficient under-
fire air should be used to burn out fixed car-
bon on the grate. Overfire air should be
introduced where it is needed to burn
volatiles, and properly cool the chamber with
a minimum entraining effect on fly ash and
particulate.
IX INFLUENCE OF PARTICULATE CONTROL
EQUIPMENT ON INCINERATOR OPERATION
If no control equipment is installed, more
careful operation of the incinerator is usually
required to try to minimize particulate
emission.
Some types of control equipment will limit
gas flow and available draft, which means
that operators may have to be careful not to
overload the incinerator. Overloading may
lead to smoke emission or positive pressure
in the incinerator.
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Good Operating Practices for Municipal Incinerator's
Operators must understand the operating
procedures required to assure that the con-
trol equipment is removing participate
efficiently.
X INFLUENCE OF WASTE COMPOSITION
VARIATIONS
Municipal incinerators receive a wide range
of waste materials varying in calorific value,
moisture content, and burning characteristics.
The operators can exercise some control
over conditions in the first chamber by
selection of material from storage.
A If temperatures soar too high, select
wet refuse.
B If temperatures drop, select dry refuse.
C If the grate speed must be reduced be-
cause of slow burning material, and
temperature is falling, select wood scrap.
If most of the refuse is wet (with unbound
moisture), overfire air will have to be
reduced and underfire air may have to be
increased. Addition of dry wood, if
available, will help maintain temperature.
Grate speed may have to be reduced.
If most of the refuse is quite dry, over-
fire air should be increased and under-
fire air reduced. It may be advisable to
spray dry refuse with water prior to
charging. The operator should remember
that per unit of volume; wood, plastics,
and rubber contain much more heat than
loose paper, garbage, or rubbish.
Because of the variations in incinerator
designs, the operating characteristics of
each plant will have to be determined by
operating personnel. Tests should be
conducted under various conditions to be
certain of the effects of operating
variables.
After establishing the type of operation
that results in the lowest emissions, the
least maintenance, with satisfactory
burning rates, this type of operation
should be made mandatory.
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"Printed with Permission of the L. A. A. P. C. D. "
MULTIPLE- CHAMBER INCINERATOR DESIGN
STANDARDS FOR LOS ANGELES COUNTY
By
JOHN E. WILLIAMSON
Senior Engineer
ROBERT J. MAC KNIGHT
Principal Engineer
ROBERT L. CHASS
Director of Engineering
OCTOBER 1960
LOS ANGELES COUNTY AIR POLLUTION CONTROL DISTRICT
PA.C. ce. 36. 1. 67
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TABLE OF CONTENTS
I.
II.
III.
IV.
V.
VI.
VII.
VIII.
IX.
X.
XI.
XII.
XIII.
INTRODUCTION . . .
CLASSIFICATION OF REFUSE ..........
PROCESS DESCRIPTION . . ,
PRINCIPLES OF COMBUSTION ..........
IGNITION CHAMBER ,
MIXING AND COMBUSTION CHAMBERS ,
DESIGN TYPES AND LIMITATIONS ........
DESIGN STANDARDS FOR NORMAL REFUSE
INCINERATORS ,
DESIGN CALCULATIONS
STANDARDS FOR CONSTRUCTION. ......
OPERATION
CONCLUSIONS
REFERENCES '.
Page^
, . 1
. . 3
, . 4
7
9
12
14
17
, , 20
26
29
31
. . 32
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I. INTRODUCTION
Disposal of combustible refuse and garbage is one of the most perplexing
problems facing urban society today. The greater the population density
the more disturbing the problem. This refuse is created by ail elements
of a community--industry, commerce, and the public.
In the past, disposal of combustible wastes was looked upon as a neces-
sary evil to be accomplished as cheaply as possible. Industrial and com-
mercial installations utilized a box-like, single-chamber type, incinerator
to burn up to several tons a day. Refuse from apartment houses was
generally burned in a chute-fed, single-chamber incinerator. In some
areas, especially Southern California, each homeowner disposed of his
combustible refuse in a backyard type incinerator.
During the past fifteen years almost every large urban area in the world
has experienced a drastic increase in the pollution of its atmosphere.
As the discomforts of air pollution became more noticeable, public
clamor for rigid regulation of air contaminating processes increased
steadily. In Los Angeles County this led to the banning of open fires
and single-chamber type incinerators in September of 1957. Since that
date all incinerators constructed and put into operation in the County
must meet stringent criteria of performance!/as well as definite mini-
mum design requirements.
Multiple-chamber incineration is a term fast becoming familiar in air
pollution control work and rapidly assuming meaning to thousands of
people who wouldn't have known what a "single-chamber incinerator"
was five years ago. No discussion of multiple-chamber incinerators
would be complete without showing to some degree how this awareness
has come about.
Early in the evaluation of sources of air pollution in Los Angeles County,±/
incineration was determined to be a major contributor. Contaminants
from open burning and single-chamber incineration^/ were found to range
from solid matter of various particle sizes, through liquid organic com-
pounds, to gaseous organic, sulfur, and nitrogen compounds. 2J
The need for a satisfactory means of refuse disposal at the source re-
sulted in an investigation of incineration in all its aspects. The object
was to develop an efficient combustion furnace that would provide maxi-
mum reduction in waste bulk with minimum emission of air contaminants
-1-
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and be capable of stable operation over a wide range of fuel mixtures and
operating conditions.
With the growing need for incinerators capable of complying with air pol-
lution codes and restrictions, it has become necessary to provide design
data that will help make satisfactory incinerators available. Recommen-
dations and standards are offered here to assist air pollution control
officials faced with incineration problems, architects and engineering
designers who must provide adequate designs, and manufacturers or con-
tractors who will, perhaps, design as well as build incinerators which
must meet air pollution control regulations. It must be cautioned that
only those qualified in combustion equipment design and refractory con-
struction should try to apply the standards presented. Adequacy of
design, proper methods of construction, and quality of materials are
important to the satisfactory completion of an incinerator that will meet
air pollution control requirements and have an average service life
expectancy.
The design standards presented in this treatise are tools to create designs
for multiple-chamber incinerators that may be expected to burn rubbish
with a minimum discharge of air contaminants. Tabular presentations
alone are not sufficient for the best application and understanding of the
principles and philosophies of design involved. It is also essential to
understand the many factors that created the need for a new approach to
incineration and the development of the multiple-chamber incinerator.
The design recommendations and supplementary discussions provide
answers to many of the questions that confront designers and operators
of multiple-chamber equipment.
-2-
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II. CLASSIFICATION OF REFUSE
It is necessary in incineration designs not only to specify the general
type of refuse but also to note specific properties such as composition
and moisture content. For purposes of incineration combustion calcu-
lations, most refuse may be considered as reacting stoichimetrically
as cellulose without serious error.
The multiple-chamber incinerator may serve nearly all incineration
requirements involving refuse consisting primarily of dry rubbish
(paper, rag and cardboard waste) with smaller amounts of wood, saw-
dust, shrubbery, green foliage and garbage. General refuse, for pur-
poses of clarification and flexibility in application, is defined as refuse
with component proportions of wide range within approximate limits as
follows:
Per cent by weight
Minimum Maximum
Dry rubbish 50 - 100
Wood, scrap 0 - 40
Shrubbery 0 - 30
Garbage 0 - 30
Sawdust, shavings 0 - 10
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III. PROCESS DESCRIPTION
The configuration of multiple-chamber incinerators may be traced back
many years to the design of multiple-cell incinerators for both municipal
and industrial waste disposal. "L"-shaped incinerators, vertically ar-
ranged incinerators, and incinerators with separate chambers have
appeared as varieties of the basic designs when circumstances or
designers have so dictated. Reduced to the simplest forms, each style
has certain characteristics with regard to performance and construction
that limit its application.
The configuration of multiple-chamber incinerators falls into two general
types, as shown in Figures 1 and 2. These are the retort type, named
for the return flow of gases through the "U" arrangement of a component
chamber; and the in-line type, so-called because the three chambers fol-
low one after the other in a line.
The combustion process proceeds in two stages--primary or solid fuel
combustion in the "ignition chamber," followed by secondary or gaseous
phase combustion. The secondary combustion zone is composed of two
parts, a downdraft or "mixing chamber" and an up-pass expansion or
"combustion chamber." Flow through the two-stage process is as fol-
lows:
a. The ignition chamber reaction includes the drying, ignition
and combustion of the solid refuse. As the burning pro-
ceeds, the moisture and volatile components of the fuel are
vaporized and partially oxidized in passing from the ignition
chamber through the "flame port" connecting the ignition
chamber with the mixing chamber.
b. From the flame port, the products of combustion and vola-
tile components of the refuse flow through the mixing cham-
ber where secondary air is induced. The combination of
adequate temperature and additional air, augmented by mix-
ing chamber or "secondary" burners as necessary, assist
in initiating the second stage of the combustion process.
Turbulent mixing, resulting from restricted flow areas
and abrupt changes in flow direction, furthers the gaseous
phase reaction. In passing through the "curtain wall port"
from the mixing chamber to the final combustion chamber
the gases undergo additional changes in direction accom-
panied by expansion and final oxidation of combustible
-4-
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IGNITION CHAMBER
MIXING CHAMBER
COMBUSTION
CHAMBER
FIGURE 1. CUTAWAY OF A RETORT MULT IPLE-CHAMBER INCINERATOR
COMBUSTION CHAMBER
IGNITION CHAMBER
BREECHING
FIGURE 2. CUTAWAY OF AN IN-LINE MULT I RLE-CHAMBER INCINERATOR
-5-
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components. Fly ash and other solid paniculate matter
are collected in the combustion chamber by wall impinge-
ment and simple settling.
c. The gases finally discharge through a stack or a combina-
tion of a gas cooler, e.g., a water spray chamber, and
induced draft system. Either draft system must limit
combustion air to the quantity required at the nominal
capacity rating of the incinerator.
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IV. PRINCIPLES OF COMBUSTION
Due to the heterogeneous nature of wastes found in refuse many factors
are involved which cannot be predicted accurately except on an empirical
basis. Theoretical treatment of the complex reactions taking place in
combustion processes is as yet incomplete, but the empirical art of com-
bustion engineering has developed to an advanced state. The principles
of solid fuel combustion generally apply in incineration and basic precepts
for combustion efficiency include the following:
a. Air and fuel must be in proper proportion.
b. Air and fuel, especially combustible gases, must be
mixed adequately.
c. Temperatures must be sufficient for ignition of both
the solid fuel and the gaseous components.
d. Furnace volumes must be large enough to provide the
retention time needed for complete combustion.
e. Furnace proportions must be such that ignition temper-
atures are maintained and fly ash entrainment is mini-
mized.
The problem of fuel quality fluctuation is one of the factors that makes
satisfactory incinerator design difficult. In addition to the wide ranges
of fuel composition, wetness and volatility, there is diversity in ash
content, bulk density, heats of combustion, burning rates and component
particle sizes. All of these affect, to some extent, the operating vari-
ables of flame propagation rate, flame length, combustion air require-
ments and the need for auxiliary heat.
The ignition mechanism should be basically one of fuel-bed surface com-
bustion. This is attained by the predominant use of overfire combustion
air and charging to attain concurrent travel of both air and refuse with
minimum admission of underfire combustion air. The importance of
limiting the admission of underfire air, and thereby maintaining rela-
tively low fuel-bed temperatures, has been postulated from analyses of
the solid particulate matter discharged when an overtired ignition mech
anism was used. With a high air rate through the fuel bed, the stack
effluent was found to contain appreciable quantities of metallic salts an ;
-7-
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oxides in microcrystalline form. This led to the theory that, with high
fuel-bed temperatures, vaporization of metals occurs accompanied by
vapor phase reactions and followed by particle condensation in the cool-
ing effluent gases as they leave the stack.
To accomplish fuel-bed surface combustion through the use of overfire
air, the charging door should be located at the end of the ignition cham-
ber farthest from the flame port, and fuel should move through the igni-
tion chamber from the front to the rear. In this way, the volatiles from
the fresh charge pass through the flames of the stabilized and heated
portion of the burning fuel bed. In addition, the rate of ignition of un-
burned refuse is controlled, preventing the flash volatilization, flame
quenching and smoke creation that attend top and side charging methods.
The use of top or side charging is no longer considered acceptable be-
cause of the suspension of dust, disturbance of the stabilized fuel bed
and additional stoking required.
With good control of the burning rate through proper charging, air port
adjustment, and use of an ignition or "primary" burner, the need for
stoking will be reduced to that necessary for fuel-bed movement prior
to charging. Control of the combustion reaction and reduction in the
amount of mechanically entrained fly ash are most important in the ef-
ficient design of a multiple-chamber incinerator.
-8-
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V. IGNITION CHAMBER
Fundamental relationships for parameter evaluation were derived by
Rose and Crabaugh^/and by the ASME Subcommittee on Incineration
Design Standards. These fundamentals are:
a. Relationship of combustion air distribution to the degree
and rate of combustion attained and to the discharge of
air contaminants.
b. Relationship of furnace proportions, i.e., chambers and
ports to the degree and rate of combustion attained and to
the discharge of air contaminants.
c. The effects of temperature and furnace design on the per-
centage of acid, volatile organic, and solid contaminants
discharged and the percentage of combustibles in the solid
contaminants discharged.,
d. Relationship of combustion gas velocities to the effects on
turbulence and flame travel and to the degree of combus-
tion attained.
e. Relationship of the material burned to the formation of
acid and volatile organic compounds.
Ignition chamber parameters were regarded as basic, since solid con-
taminant discharges only could be functions of the mechanical and chem-
ical processes taking place in the primary stage. Incinerators were
tested6/ burning general refuse, as defined, with a gross heating value
of 7,500 Btu/lb or less. Formulas governing ignition chamber design
were tentatively postulated from data obtained from tests of units of vary-
ing proportions operating at maximum combustion rates.
Subsequent to the publication of the tentative formulas, additional testing
and evaluation of units consuming materials with a gross heating value of
9,000 Btu/lb revealed that the optimum formulas for the average grate
loading as well as the arch height should be increased approximately 20
per cent. The gross heating value of general refuse normally falls be-
tween 7, 500 and 9,000 Btu/lb.
-9-
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Optimum values of the arch height and grate area may be determined by
using the gross heating value of the refuse to be burned and interpolating
between the upper and lower curves given in Figures 3 and 4. An allow-
able deviation of these values of plus or minus 10 per cent is considered
to be reasonable. Rather than establish formulas for both the upper and
lower curves of Figures 3 and 4, a formula for the average values of the
two curves has been given. This curve corresponds to a gross heating
value of 8,250Btu/Lb.
-10-
-------
50
40
a. 30
o
I 2°
o
-I
10
DRY REFUSE. HIGH HEATING VALUE
+ 10%
i
-•— -10%
MOtST REFUSE. LOW HEATING VALUE
LG = 10 LOG Rc
0 2k 5 7f 10 12} 15 20 25 30 35 40 45 50
RC. COMBUSTION RATE-LBS. PER HR. •=- 100
FIGURE 3. RELATIONSHIP OF GRATE LOADING TO COM-
BUSTION RATE FOR MULT I RLE-CHAMBER INCINERATORS
DRY REFUSE. HIGH HEATING VALUE
MOIST REFUSE. LOW HEATING VALUE
4 4/11
H = _ (A )
3
20 40 60 80 100 120 140 160 180 200
AG. GRATE AREA-SO.FT.
FIGURE 4. RELATIONSHIP OF ARCH HEIGHT TO GRATE AREA FOR MULTIPLE-CHAMBER INCINERATORS
-11-
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VI. MIXING AND COMBUSTION CHAMBERS
In the process of confirming the parameter relationships in the ignition
chamber, the factors controliing the design of the gas phase combustion
zone were aiso developed. Application of the fundamental evaluation
precepts combined with trials of various proportions in both chamber
and port dimensions and secondary air admission established parameters
for the mixing and combustion chamber portions of the multiple-chamber
incinerator. The primary effect of proper design has been attainment of
a higher degree of completion of combustion of volatile and solid combus-
tible effluent components. By designing the combustion chamber as a
settling chamber it has been possible to achieve some reduction in fly ash
emissions as well.
Basic Parameters
Incinerator design factors which have been selected as basic include the
ratios of combustion air distribution, supplementary draft and tempera-
ture criteria, and ignition chamber length-to-width ratios as well as the
ignition chamber parameters and the secondary combustion stage veloc-
ity and proportion factors. Some of these factors are functions of the
desired hourly combustion rate and are expressed in empirical formulas,
while others are assigned values which are independent of incinerator
size.
The values determined for the several parameters are mean empirical
values, accurate in the same degree as the experimental accurach of the
evaluation tests. The significance of exact figures is reduced further by
the fluctuation of fuel composition and conditions. For purposes of
design, permissible variations from the optimum mean are plus or minus
10 per cent, and velocities may deviate as much as 20 per cent without
serious consequences.
Table I, Multiple-Chamber Incinerator Design Factors, lists the basic
parameters, evaluation factors and equations, and gives the optimum
values established for each.
-12-
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TABLE I
MULTIPLE-CHAMBER INCINERATOR DESIGN FACTORS
ITEM AND SYMBOL
RECOMMENDED VALUE
HF.VIATION
A. Primary Coatbuition Lone:
L . Grate loading, LG
2. Crete arc*. AC
3. A*erage areK he ight. H*«
4. Length to width ratio (approx.):
•. Retort
b. In-line
10 Log RC : Ibs/hr-ft** where RC equal* the refuae combustion rite io Ibs/hr
RC « LC: fl2
l: ft(refer to Fig.«)
Up to 500 lb»/hr,2:l; over SOO Iba/hr . 1 . 75 : 1
Diminishing from about 1.6:1 for 750 Iba/hr to about 1:1 for 4.000 Iba/hr
aquare acceptable in unit* of more than 11 ft ignition chamber length.
(refer to Fig. 3)
capacity. Over-
1 10*
1 10*
B. Secondary Combust ion Zone :
1. Gas Velocities:
.. Flsae port • 1000°F. Vpp
b. Miw.ng ch»b«r C 1000°F. VHQ
c. Curtwiin ••!! port * 950°F. VQyp
d. Coabu.it.on chamber 6 900°F. VCC
2. Mixing cKtober downpt.as length. L-vf)
top of curtain wall port.
3. Length to width ratios of flow cro»»-aection»:
a. Retort, aixing chamber and coabuation chanber
b. In-line
from top of ignition chamber arch to
55 fl/aec
25 ft/aec
About 0.7 of aixing chanber velocity
5 to 6 fl/aec: alwaya leaa than 10 ft/aec
Average arch height, ft
Range - 1.3:1 to 1.5:1
1 20)1
1 20*
1 201
C. Coabuation Air:
.. Air requirement batch charging operation
2. Combo*tion air distribution:
a. Ore rfi re air port*
b. Underfire air porn
c. Mixing chamber air ports
3. Port ailing, nominal inlet velocity press
4. Air inlet ports o*er.iie factors:
.. Primary .ir inlet
b. Underfire sir inlet
c. Secondary •.r inlet
Basia: 300% excess air. 50% air requirement admitted through adjustable porta; 50% air
requirement met by open charge door and leakage
70% of total air required
10% of total air required
20% of total sir required
0.1 inch water gage
1.5 for over 500 Ibs/hr to 2.5 for 50 Ibs/hr
2.0 for over 500 Iba/hr to 5.0 for SO Ibs/hr
O. Furnace Temperature:
ombuation producta
1000°F
1 20°F
E. Auxiliary Burners:
Noraisl duly require
1. Pr in-iry burner
bv
1250-2500
2500-5000
F. Drafl Requirement!<_:
\. Theoretic... atack draft. Or
2. Availsble prinary sir induction draft. D\. (Assume equivalent to inlet
al draft
0.2*0.35 inch water gage
0.1-0.2 inch water gage
Less lhan 30 fl/aec 9 900°F
-------
VII. DESIGN TYPES AND LIMITATIONS
During the evaluation and development phases of the multiple-chamber
incinerator, different incinerator configurations were tested with vari-
ations in the sizes and shapes of the several chambers and ports. When
tests indicated optimum performance on a contaminant discharge basis,
and visual inspection revealed satisfactory flame travel, flame coverage
and fly ash control, the characteristics of the incinerator were noted and
the design limitations and parameters were established. The results of
these tests, while providing data for development of design factors, also
showed the optimum operating limits for the two basic styles of multiple -
chamber incinerators.
Retort Type
Essential features which distinguish the retort type of design are:
a. The arrangement of the chambers causes the combustion
gases to flow through 90° turns in both lateral and verti-
cal directions.
b. The return flow of the gases permits the use of a common
wall between the primary and secondary combustion stages.
c. Mixing chambers, flame ports and curtain wall ports have
length-to-width ratios in the range from 1:1 to 1.5:1.
d. Bridge wall thickness under the flame port is a function of
dimensional requirements in the mixing and combustion
chambers. This results in construction that is somewhat
unwieldy in the size range above 500 pounds per hour.
In-Line Type
Distinguishing features of the in-line design are:
a. Flow of the combustion gases is straight through the incin-
erator with 90° turns in only the vertical direction.
-14-
-------
b. The in-line arrangement of the component chambers gives
a rectangular plan to the incinerator. This style is readily
adaptable to installations which require separated spacing
of the chambers for operating, maintenance or other
reasons.
c. All ports and chambers extend across the full width of the
incinerator and are as wide as the ignition chamber.
Length-to-width ratios of the flame port, mixing chamber
and curtain wall port flow cross-sections range from
3:1 to 5:1.
Comparison of Types
A retort incinerator in its optimum size range offers the advantage of
compactness and structural economy that are permitted by its cubic
shape and a reduction in exterior wall length. It has been demonstrated
that the retort incinerator performs more efficiently than its in-line
counterpart in the capacity range from 50 pounds per hour to about 750
pounds per hour. The in-line incinerator is well suited to high capacity
operation but is not too satisfactory for service in small sizes. The
smaller in-line incinerators are somewhat less efficient with regard to
secondary stage combustion than retort type. The capacity range in
which the in-line incinerator is found to function best is from 1000 pounds
per hour to whatever limit is imposed by practicability.
The incinerator type capacity recommendations overlap at the 750-1000
pounds per hour capacity level and there are no outstanding factors which
favor either in this size range. The choice of in-line or retort is dictated
by personal preference, space limitations and, perhaps, the nature of the
refuse and charging conditions.
The basic factors which tend to cause a difference in performance in the
two incinerator types are: (1) proportioning of the flame port and mixing
chamber to maintain adequate gas velocities within dimensional limita-
tions imposed by the particular type involved, (2) maintenance of proper
flame distribution over the flame port and across the mixing chamber,
and (3) flame travel through the mixing chamber into the combustion
chamber.
The additional turbulence and mixing promoted by the turns in the retort
incinerators cause the nearly square cross-sections of the ports and
chambers in small size units to function adequately. In the retort size
-15-
-------
range above 1000 pounds per hour the reduced effective turbulence in
the mixing chamber caused by the increased size of the flow cross-
section results in inadequate flame penetration, distribution and second-
ary air mixing.
As the capacity increases, the in-line model exhibits structural and per-
formance advantages. Certain weaknesses of the small in-line type are
eliminated as the size of the unit increases. For instance, with an in-
line incinerator of less than 750 pounds per hour capacity, the shortness
of grate length tends to inhibit flame propagation across the width of the
ignition chamber. This, coupled with thin flame distribution over the
bridge wall, may result in the passage of smoke from smoldering grate
sections straight through the incinerator and out of the stack without
adequate mixing and secondary combustion. In-line models in sizes of
750 pounds per hour or larger have grates long enough to maintain burn-
ing across their width resulting in satisfactory flame distribution in the
flame port and mixing chamber. Since smaller in-line incinerators have
relatively short grates, a problem of construction is added. As the
bridge wall usually is not provided with any structural support or back-
ing, and secondary air lanes are built into it, the wall is very suscept-
ible to mechanical abuse. Careless stoking and grate cleaning in short
chambered in-line incinerators can ruin the bridge wall in a short time.
No upper limit has been given the use of the in-line incinerator as little
is known of operating efficiencies in capacities of over 4 tons per hour.
Incinerators in the capacity range under 2000 pounds per hour may be
standardized for construction purposes to a great degree. Incinerators
of larger capacity, however, are not readily standardized as problems
of construction, material usage, mechanized operation with stoking
grates, induced draft systems, and other factors make each such instal-
lation essentially one of custom design. Even so, the design factors
advocated herein are as applicable to the design of larger incinerators
as to the design of smaller units.
-16-
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VIQ. DESIGN STANDARDS FOR NORMAL REFUSE INCINERATORS
Dimension standards presented in Figures 5 and 6 for retort and in-
line incinerators are based upon recommended factors and parameters.
The development of the standards was in accord with the following design
notes:
a. Refuse: Normal refuse as defined.
b. Construction:
(1) Retort or in-line style constructed of standard pre-
fired refractory firebrick with unspecified exterior
shell construction.
(2) Arch height and other vertical dimensions are aver-
ages based on construction with 60° sprung arches.
(3) Sizes listed for ports shown as circular are nominal
diameters of round air inlet spinners which have 35
to 50 per cent net open flow areas. Allowances must
be made to provide equivalent areas in other port
styles.
The dimensions itemized will vary in some cases from optimum values
due to the elimination of partial or "cut" firebrick in wall construction.
All dimensions are nominal, since brick construction tolerances vary.
Dimension allowances must be made when construction differs from
that used as the basis for the standards, i.e., flat or suspended arches
instead of sprung arches; square or rectangular stack cross-sections
instead of round. Average arch heights and recommended flow areas
must be maintained.
External construction must be adequate structurally for the support of
the refractory materials, with proper allowances for expansion and
insulation. Foundation and stack construction details should be in ac-
cord with good structural practices and in conformance with local build-
ing ordinances.
-17-
-------
PLAN VIEW
SIDE ELEVATION
I. STACK
2. SECONDARY AIR PORT
3. GAS BURNERS
4. ASH PIT CLEANOUT DOOR
5. GRATES
6. CHARGING DOOR
7. FLAME PORT
8. UNDERFIRE AIR PORT
9. IGNITION CHAMBER
10. OVC&FIRE AIR PORT
11. MIXING CHAMBER
12. COMBUSTION CHAMBER
13. CLEANOUT DOOR
14. CURTAIN WALL POHT
I 1
END ELEVATION
SIZE OF INCINERATOR
POUNDS PER HOUR
LENGTH IN INCHES
ABCDEFGH'I JKLMNOPQRSTUVWXYZ
50
100
150
250
500
750
1000
314
»0i
45
54
764
85i
9*i
134
18
224
27
36
494
54
224
284
334
374
474
94
594
9
134
154
18
27
36
36
6i
9
114
134
18
224
27
20*
27
29
36
494
54
584
134
18
224
27
36
45
45
18
19
20
22
28
32
3«
8
12
14
18
24
30
3»
184
23
27
30
364
40
45
20
28
354
40
484
514
544
31
5
5
74
124
15
174
10
15
164
18
23
28
30
»4
24
44
44
9
9
9
2i
24
24
44
»4
44
44
2i
4
44
44
44
44
44
9
144
18
20
26
25
274
24
5
5
5
5
5
74
24
0
24
24
5
10
124
24
24
24
24
24
24
24
44
44
44
44
9
9
9
24
24
24
24
44
44
44
44
44
44
44
9
9
9
44
44
44
44
9
9
9
6
8
9
12
16
18
22
4
5
6
6
8
8
10
'dimension "H " given ir feet.
FIGURE 5. DESIGN STANDARDS FOR MULT IPLE-CHAMBER RETORT INCINERATORS
-18-
-------
>^tev:N\^>o -,
AyX'-vX-SSfX'-
' ,/ '/• ,'/
H
t
PLAN VIEW
SIDE ELEVATION
1. STACK
2. SECONDARY AIR PORTS
3. ASH PIT CLEANOUT DOORS
4. GRATES
5. CHARGING DOOR
6. FLAME PORT
7. IGNITION CHAMBER
8. OVERFIRE AIR PORTS
9. MIXING CHAMBER
10. COMBUSTION CHAMBER
I I . CLEANOUT DOORS
12. UNDERFIRE AIR PORTS
13. CURTAIN WALL PORT
14. DAMPER
15. GAS BURNERS
SIZE OF INCINERATOR
POUNDS PER HOUR
LENGTH IN INCHES
ABCDEFGHIJKL*MNOPQRSTUVWXY
750
1000
1500
2000
854
9*1
99
108
49*
54
76i
90
51i
94
65
69i
45
474
55
57*
151
18
18
22*
5*
63
72
794
27
31*
36
404
27
314
36
404
*o
94
11
124
15
24
29
32
36
18
224
27
314
32
35
38
40
44
44
44
44
5
5
5
5
74
10
74
10
9
9
9
9
24
24
44
44
24
24
44
44
30
30
30
30
9
9
9
9
44
44
44
44
5
7
8
9
11
12
14
15
51
52
614
634
7
8
9
10
mension "L" given in feet.
FIGURE 6. DESIGN STANDSRDS FOR MULTIPLE-CHAMBER IN-LINE INCINERATORS
-19-
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IX. DESIGN CALCULATIONS
To use the factors itemized in Table I, calculations must be made that
will yield incinerator data in usable form. The calculations fall into
three general categories: (1) combustion calculations based upon the
refuse composition, assumed air requirements and estimated heat loss,
(2) flow calculations based unon the properties of the products of com-
bustion and assumed gas temperatures, ami (3) dimensional calcula-
tions based upon simple mensuration and empirical sizing equations.
Simplifying assumptions that are made ir. connection with the incinera-
tion process should be reasonable esiimate.c of conditions known to
exist. Their value lies in the resultant ease of application of the calcu-
lated data in preparing incinerator designs and comparing them with the
established parameters and with similar satisfactory units. The simpli-
fying assumptions upon which calculations arc based may be summarized
as follows:
a. The burning rate and average refuse composition are
taken as constant. An exception may be required when
extremes in material qualm n.id composition are en-
countered. The most difficult burning condition is
assumed in such cases.
b. The average temperature of the combustion products
is determined through normal heat loss calculations
except that losses due to radiation, refractory heat
storage and residue heat content are assumed to aver-
age 20-30 per cent of the gross heating value of the
refuse during the first hour of operation. Furnace data
generally available indicate that the losses approximate
10 to 15 per cent of the gross heat after four to five
hours of continuous operation.
c. The overall average gas temperature should be about
1000°F when calculations are based on 300 per cent
excess combustion air and the heat loss assumptions
previously given. The calculated temperature is not
flame temperature and does not indicate the probable
maximum temperatures attained in the flame port or
mixing chamber. Should the temperature be lower, the
need for auxiliary primary burners is indicated and
should be sized as indicated in Table I.
-20-
-------
The temperatures used in checking gas flow velocities are
approximations of the actual temperature gradient in the
incinerator as the products of combustion cool as they pass
from the flame port to the stack outlet.
d. Indraft velocities in the combustion air ports (overfire,
underfire and secondary) are assumed to be equal, with
a velocity pressure of 0.1 inch water column (equivalent
to 1,265 ft. per min.). Control in design of the draft
system so that available firebox draft is about 0.1 inch
water column and oversizing of adjustable air ports
insures maintenance of proper air induction.
e. Air ports must be sized for admission of theoretical air
plus 100 per cent excess air. The remaining air enters
the incinerator through the open charging door during
batch operation and through expansion joints, cracks
around doors, etc.
The combustion calculations needed to determine weights and velocities
of the products of combustion and average temperatures may be derived
from standard calculation procedures when the preceding assumptions
are followed, using average gross heating values and theoretical air
quantities. The sizing of inlet air areas in the proportions designated
is accomplished readily once the volumes of air and inlet velocities are
established. The minimum areas required should be oversized in prac-
tice by the factor indicated in Table I in order to provide operational
latitude.
Determination of velocities requires only volume and temperature data
for the products of combustion and the cross-sectional flow areas of the
respective ports and chambers. Calculations for draft characteristics
follow standard stack design procedures common to all combustion engi-
neering. The stack velocity given for natural draft systems is in line
with good practice and minimizes flow losses in the stack.
The remainder of the essential calculations needed to design an inciner-
ator are based on substitution in the parameter equations and measure-
ment of the incinerator dimensions. Recommended grate loading, grate
area and average arch height may be calculated by equation or estimated
from Figures 3 and 4. Proper length-to-width ratios may be determined
and compared with proposed values.
-21-
-------
Supplementary computations are usually required in determining neces-
sary auxiliary gas burner sizes and auxiliary fuel supply line piping.
Where moisture content of the refuse is less than 10 per cent by weight,
burners usually are not required. Moisture content from 10 to 20 per
cent normally will indicate the necessity of installation of mixing cham-
ber burners, and moisture percentages of over 20 per cent usually will
mean that ignition chamber burners must be included.
The criteria presented for incinerator design are applicable to the plan-
ning of most combustible refuse burners. The allowable deviations
given in Table I should be interpreted with discretion to avoid consist-
ently high or low deviation from the optimum values. Application of
these factors to design evaluation must be tempered by judgment and by
an appreciation of the practical limitations of construction and economy.
The following example shows the mathematical calculations necessary to
design an incinerator.
Problem:
Design a multiple-chamber incinerator to burn
100 Ibs/hr of paper with 15 per cent moisture.
Given:
Specific heat of products of combustion--0.26 Btu/lb/°F
Gross heating value of one pound dry paper--7590 Btu
0. 56 Ib of water formed from the combustion of -1 pound
of dry paper
21.7 pounds of products of combustion formed from the
combustion of 1 pound of paper with 300 per cent
excess air
68.05 scf of air theoretically necessary to burn 1 pound
of dry paper
1265 fpm is equivalent to velocity pressure of 0.1 inch
283. 33 scf of products of combustion formed from the
combustion of 1 pound of paper with 300 per cent
excess air
0.0092 inch of theoretical draft per foot of stack at
-22-
-------
Solution:
1. Composition of refuse
Dry combustibles (100 Ibs/hrXO. 85)
Moisture (100 Ibs/hr )(0.15)
2. Gross heat of combustion
(85 lbs/hr)(7590 Btu/lb)
3. Heat losses
85 Ibs/hr
15 Ibs/hr
= 645,200 Btu/hr
Radiation, etc.(0.20)(645,200 Btu/hr) - 129,040 Btu/hr
Evaporation of contained moisture
(15 lbs/hr)( 1060 Btu/lb)
Evaporation of water from combustion
(0. 56 lb/lb)(85 lbs/hr)(1060 Btu/lb)
Total
4. Net heat
645,200 Btu/hr - 195, 340 Btu/hr
5. Weight of products of combustion
with 300 per cent excess air
Paper (85 lbs/hrX2l.7 Ibs/lb)
Water 15 Ibs/hr
6. Average gas temperature
449,860 Btu/hr
T • (0.26 Btu/lb/uF) (1859 Ibs/hr)
T = 930°F + 60°F
7. Combustion air requirement
- 15,900 Btu/hr
- 50,400 Btu/hr
195,340 Btu/hr
449,860 Btu/hr
1,844 Ibs/hr
15 Ibs/hr
1, 859 Ibs/hr
930°F
990°F
Basis: 300 per cent excess air. 50 per cent of the air
is admitted through open charging door and leak-
age around doors, ports, expansion joints, etc.
-23-
-------
Combustion air
(85 lbs/hr)(68.05 cf/lb)(2) = u, 580 cfh
192. 8 cfm
3. 2 cfs
8. Air port opening requirements @ O.I" we
Total (192.8cfm)(144in2/ft2) . 22 Q in2
1265 ft/min
Overfire air port (0. 7)(22. 0 in2) • 14. 5 in2
Underfire air port (0. 1X22. 0 in2) = 2. 2 in2
Secondary air port (0. 2)(22. 0 in2) = 4. 4 in2
9. Volume of products of combustion
Basis: 60°F and 300 per cent excess air
Paper (85 lbs/hrX283. 33 cf/lb) - 24, 080 cfh
Water (15 Ibs/hr) () = 3l6 cfh
18 :
24, 396 cfh
6. 8 cfs
10. Volume of products of combustion through flame port
Total volume minus secondary air
6. 8 cfs -(3.2 cfsXO.20) =• 6. 16 cfs
11. Flame port area:
(6.l6cfsX1560°F_) = o. 31 ft2
(60 ~
12. Mixing chamber area:
(6.8cfsX1460°R) _ 0 ?6 ft2
(25
-24-
-------
13. Curtain wall port area:
(68
ft2
n
(20 fps)(5200R) ~
14. Combustion chamber area:
(6 8cfs)(l3600R) 2
(0 fps)(52UuR) = ^.*°"
15. Stack area:
(6 8 cfs)(l3600R) 2
(25 fps)(520°R) = 0-71 ft
16. Grate area:
From Figure 3 grate loading for average refuse
is 18 Ibs/ft2/hr
(lOOlbs/hr) . 5.56ft2
18 lbs/ft-/hr
17. Arch height:
From Figure 4: 2'3"
18. Stack height:
0. 17 inches we
0.0092 inches we
18'6"
-25-
-------
X. STANDARDS FOR CONSTP UCTION
Mechanical design and construction of multiple-chamber Incinerators are
regulated in several ways. Ordinances and statutes which wet forth basic
building requirements have been established by most, if not all. munici-
palities. Air pollution control authorities have also set some material
and construction limitations which must be met: and manufacturers'
associations have established recommended minimum standards to be
followed. The building codes governing incinerator construction adopted
in the past have been based primarily upon concepts of structural safety
and fire prevention by restricting the rate of heat transfer through the
walls. Little or no attention was given to the abrasion, erosion, spalling,
and slagging that are encountered in a high temperature incinerator; yet
these conditions lead to equipment failure which are comparable to struc-
tural or insulation failures. During the process of developing multiple-
chamber units it has been found that high quality materia,s are necessary
if a reasonable and satisfactory service life is to be expectel
The structural features and materials used in Lie cons^rucdon of muitiple-
chamber incinerators can be discussed only in general terms. There are
as many methods of erecting the walls of a multiple-changer incinerator
as there are materials from which to build them. The exterior of the
incinerator may be either of brick or steel plate constraction, and the
refractory lining may be of firebrick, castable refractory or plastic
firebrick or combinations thereof.
In accordance with standard practices, the exterior walls are protected
further from extreme temperature conditions by providing a suitable
peripheral air space in brick construction, or by using air cooling lanes
or insulation in units fabricated from steel.
Changes in the methods of construction of multiple-chamber incinerators
are typified in the portable prefabricated units available today. Installa-
tion of such Incinerators is reduced simply to placement of the unit on
its foundation and attachment of an auxiliary fuel supply where needed.
Transportation considerations of weight and size limit the capacities of
these units to 500 pounds per hour or less. Plastic and castable refrac-
tory linings in steel exteriors are used widely for this type of fabrica-
tion. All large incinerators of any type construction and those for which
brick is desired as an exterior wall are erected on the site.
-26-
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Refractory
The most important element of multiple-chamber Incinerator construc-
tion, other than the design, is the proper installation and use of refrac-
tories. It is imperative that manufacturers use suitable materials of
construction and be experienced in high temperature furnace fabrication
and refractory installation, as faulty construction may well offset the
benefits of good design. In choosing one of many available materials,
service conditions alone should dictate the type of lining for any furnace.
Minimum specifications of materials in normal refuse service should
include high heat duty firebrick or 120 pounds per cubic foot castable
refractory. These materials, when properly installed, have proved
capable of resisting the abrasion, spalling, slagging and erosion result-
ing from High temperature incineration.
As incinerator capacity and severity of duty increase, superior refrac-
tory materials such as super duty firebrick and plastic firebrick should
be employed. A recent improvement in standard construction has been
the lining of all stacks with a 2000°F refractory lining of 2-inch mini-
mum thickness.
Grates and Hearths
The grates commonly used in multiple-chamber incinerators are cast
iron with "tee" or channel cross-section. As the size of the incinerator
increases, the length of the ignition chamber also increases. In the
larger hand-charged incinerators, is is difficult to keep the rear section
of the grates completely covered because of the greater length of the
ignition chamber. The substitution of a hearth at the rear of the ignition
chamber in these units has been accepted as good practice, as a hearth
in this region prevents open areas from being formed in the normally
thin refuse pile. This prevents excessive underfire air from entering
in front of the bridge wall and reduction of flame carryover into the
mixing chamber. As surface combustion is the primary combustion
principle, the use of a hearth has little effect upon the combustion rate.
Installation of a sloping grate, which slants down from the front to the
rear of the ignition chamber, facilitates charging. Such a grate also
increases the distance from the arch to the grates at the rear of the
chamber and reduces the possibility of fly ash entrainment which fre-
quently occurs when the fuel bed surface approaches the level of the
flame port.
-27-
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Air Inlets
Positive control for all combustion air inlets should be provided by
means of fully adjustable dampers. The retort incinerator designs
shown in Figure 5 incorporate round spinner type controls with rotating
shutters for both underfire and overfire air openings and rectangular
ports with sliding or hinged dampers for the secondary air openings.
The in-line incinerator designs shown in Figure 6 have rectangular
ports for both overfire and secondary air openings and spinner style
ports for the underfire air openings. Air ports may be of any conven-
ient shape although the port arrangement indicated in the in-line designs
with rectangular overfire ports is preferred since the combustion air is
distributed more evenly across the fuel bed.
Stack Construction
Stacks for incinerators with a capacity of 500 pounds per hour or less
are usually constructed of a steel shell lined with refractory and
mounted over the combustion chamber. A refractory lined, reinforced
red brick stack is used as an alternate method of construction when
appearance is deemed important. Stacks for incinerators larger than
500 pounds per hour are normally constructed in the same .manner as
those for smaller incinerators but often are free-standing for structural
stability, as indicated in Figure 6. Stack linings should be of increased
thickness in proportion to the incinerator size.
Induced Draft
The replacement of a stack by an induced draft system introduces com-
plications. It is necessary to cool the effluent gases to reduce their
temperature to that for which the draft fan is rated. Evaporative cool-
ing with water is standard practice. The contact of the flue gas with
water forms a solution of weak acid. The action of the acid eventually
corrodes the evaporative cooler and accessory equipment, making
replacement necessary. To overcome these problems, stainless steel
or acid resistant brick may be installed. The excess spray water also
creates a problem, requiring a sewer outlet for its disposal or a re-
circulation system for its re-use. Recirculation of acidic water not
only results in more rapid corrosion of the spray chamber and fan,
but also subjects the pump, piping and spray nozzles to corrosion.
-28-
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XI. OPERATION
The most important single aspect of operation of a multiple-chamber
incinerator is the charging of refuse into the ignition chamber. A multi-
ple-chamber incinerator must be charged properly at all times in order
to reduce the formation of fly ash and to maintain adequate flame cover-
age of the burning rubbish pile and the flame port.
A recommended charging cycle starts with the placing of the initial
charge of refuse in the incinerator. The ignition chamber should be
filled to a depth approximately two-thirds to three-fourths of the distance
between the grates and the arch prior to light-off. After approximately
half of the refuse has been burned, the remaining refuse should be care-
fully stoked and pushed as far as possible to the rear of the ignition cham-
ber. New refuse should be charged over the front section of the grates
which were emptied by the moving of the burning refuse. To prevent
smothering the fire, no new material should be charged on top of the
burning refuse at the rear of the chamber. Using this charging method,
"live" flames will cover the rear half of the chamber, fill the flame port
and provide nearly complete flame coverage in the mixing chamber. The
fire will propagate over the surface of the newly charged material, spread-
ing evenly and minimizing the possibility of smoke emission. Since the
refuse pile need not be disturbed unduly, little or no fly ash will be
emitted.
It is characteristic of the multiple-chamber incinerator that emission
control is built-in, if it is operated with reasonable care. The discharge
of combustion contaminants is almost entirely a function of ignition cham-
ber design and the actions of the operator. Control of smoke is attained
by proper admission of combustion air and by utilization of secondary
burners in cases of incineration of refuse with a low heating value or a
high moisture content. The use of secondary burners is required at
times as the efficiency of the mixing chamber depends upon both luminous
flame and adequate temperatures for vapor phase combustion. The need
for supplementary burners may be determined readily by observing the
nature of the flame travel and coverage at both the flame port and the
curtain wall port.
The overfire and underfire air ports are usually half open at light-off
and are opened gradually to a full open position as the incinerator
reaches its rated burning capacity. If black smoke is emitted, it is
advisable to admit more secondary air and reduce the capacity of other
air ports. On the other hand, white smoke is usually the result of too
-29-
-------
cold a furnace and may be eliminated by reducing or closing all air
ports Following the final charge of refuse, the air ports are closed
gradually so that during the burndown period the only air introduced
into the furnace is provided through leaks around door and port
openings.
When ignition and mixing chamber burners are necessary, the mixing
chamber or secondary burner is lighted prior to placing the incinerator
in operation. The burner should remain in operation for the first 15 to
20 minutes of operation, and should be used thereafter as needed.
Under normal conditions, the ignition chamber or primary burner is
used only when wet refuse is charged. At other times, its use also
may be required when burning refuse containing high percentages of
inorganic compounds such as clay fillers used in quality paper.
-30-
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XII. CONCLUSIONS
The most important item to be considered in the selection of an incinera-
tor is its capacity. A complete survey of the quantity and type of refuse
produced should be conducted and accurate weights obtained. Considera-
tion should be given to possible future expansion of existing facilities. On
the basis of this information, the size of the incinerator is determined by
the scheduled number of hours of operation.
It is also important that the site for the incinerator be selected with rea-
sonable care. Its position will be dictated primarily by the location of
existing equipment and spatial provisions necessary for convenient oper-
ation and adequate storage. Also to be considered are the proximity of
surrounding buildings, the need for incinerator mobility and the aesthetic
requirements to be met in some situations.
The purchase of an incinerator always should be by contract that explic-
itly specifies structural and refractory requirements. The contractor
should be required to guarantee that the operation of the incinerator will
comply with the statutes of all agencies and that mechanical performance,
including refractory and material service life, will be satisfactory for a
reasonable period.
Combustion engineering and furnace design authorities agree that multiple
chamber incineration combines the best means of disposing of combusti-
ble refuse at the source with a minimum emission of air contaminants.
Furnace manufacturers have found that construction of multiple-chamber
incinerators of designs that comply with air pollution control regulations
is only slightly more difficult or expensive than equivalent construction
of industrial incinerators of earlier design.
The multiple-chamber incinerator has been accepted by industry and the
public in Los Angeles County as a practical device to dispose of combus-
tible, wastes economically and within the limits of air pollution control
regulations.
-31-
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XIII. REFERENCES
1. State of California Health and Safety Code, Section 24242. 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 Ringel-
mann 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 sec-
tion.
Los Angeles County Air Pollution Control District Rules and Regula-
tions, Rule 53. Specific Contaminants. A person shall not discharge
into the atmosphere from any single source of emission whatsoever
any one or more of the following contaminants, in any state or com-
bination thereof, exceeding in concentration at the point of discharge:
(a) Sulphur Compounds calculated as sulphur dioxide (SC-2): 0*2 per
cent, by volume, (b) Combustion Contaminants: 0. 3 grain per cubic
foot of gas calculated to 12 per cent of carbon dioxide (C02) at stand-
ard conditions. In measuring the combustion contaminants from
incinerators used to dispose of combustible refuse by burning, the
carbon dioxide (CO2) produced by combustion of any liquid or gaseous
fuels shall be excluded from the calculation to 12 per cent of carbon
dioxide (CO2).
2. Chass, R. L., Lunche, R. G., Shaffer, N. R., and Tow, P. S.,
"Total Air Pollution Emissions in Los Angeles County." Presented
at the 52nd Annual Meeting of the Air Pollution Control Association,
Los Angeles, California, June 1959.
3. ChaflS, R. L., and Rose, A. H., "Discharge from Municipal Inciner-
ators." Journal of the Air Pollution Control Association (Air Repair),
Vol. 3, No. 2, November 1953.
4. MacKnight, R. J., Williamson, J. E., Sableski, J. J., and Dealy, J.O.,
"Controlling the Flue Fed Incinerator." Journal of the Air Pollution
Control Association, Vol. 10, No. 2, April I960.
5. Rose, A. H., and Crabaugh, H. R., 'Incinerator Design Standards."
A.S. M. E., First International Congress on Air Pollution Controls,
March 1955.
6. Kanter, C. V., Lunche, R. G., and Fudurich, A. P., "Techniques of
Testing for Air Contaminants from Combustion Sources." Journal of
the Air Pollution Control Association, Vol. 6, No. 4, February 1957.
-32-
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THE PROBLEMS OF APPLYING INCINERATOR CRITERIA
Edward M. Voelker
I AIR POLLUTION CONTROL AUTHORITIES
Today many communities, counties and states
have created Air Pollution Control Authorities
and the authorities have in turn adopted cri-
teria for the design of incinerators. Each
day more and more authorities are being
established and again many are adopting cri-
leria of their own. Much of the "criteria"
or "rules" are incomplete making it almost
mandatory to obtain prior approval before
making a recommendation to an architect,
engineer, or owner and certainly before bid-
ding the job.
Needless to say this in many cases is impos-
sible because of time and cost limitations,
and in other cases wheretime does permit, the
prior approval is not recognized by the ai r pol-
lution authority at the time of formal sub-
mission since he, :n the meantime, has had
some new thoughts on the subject.
In attempting to compare the criteria being
issued by these governing bodies, it becomes
immediately apparent that the air pollution
control officials arc not aware of the situations
being created by their various independent
actions. Unfortunately it is impossible to
make a direct comparison of all regulations
in effect at the present time nor for that
matter can any one individual become familiar
with all such regulations. In many cases a
direct comparison is impossible because of the
lack of some basic design factor in the publish-
ed version of the criteria, or the regulations
are changed arid quite often not in written or
published form.
The need for test procedures, and incinerator
criteria acceptable to all Air Pollution Control
Authorities is of vital importance to the in-
cinerator industry. To achieve this goal the
Incinerator Institute of America has established
liaison between its organization and the TA-3
Committee of APCA and also with the Inciner-
ator Committees of the American Society of
Mechanical Engineers and the American Gas
Association.
The Incinerator Institute of Am-.-ri.--i has also
established an assoc.ate membership for com-
panies and individual ; who are not in the in-
cinerator business h ;t whom Ui.- Institute be-
lives can contribute lo the modern requirements
of air pollution f-ontrol. We since rely invite ,;iif•'
organizations as oil mid gas burner manufac-
turers, firebrick, instrument, gas washer am.
scrubber manufacturers to join and become
active on ourtechni. ;il and standards commit!.-t -
II INCINERATOR CKlThlUA
The incinerator criteria being adopted today
by states, counties ind communities fall ini.<
two distinct c ate got ies:
A
B
The very rigid criteria i - jaliy in the form
of charts and diagrams arui covering onl\
incinerators fur Type 1 and Type 2 Wast.-.
The flexible criteria which sets forth
minima and maxima governing designs
of incinerators for burning all types of
waste.
From the viewpoint of the Air Pollution Control
Authority or Department, the rigid criteria i.-
the more acceptable because by its very nature
it is the easier and simpler to apply. The ex-
aminer, when reviewing an application, has no
problems - either the application and accom-
panying drawing conforms to tl:.- charts and
diagrams in the criteria and he approves the
application, or they do not and he rejects it.
However, such rigid criteria leave nothing to
the imagination of the incinerator designer and
certainly leave no room for meritorious
improvements.
Eventually the responsibility for the design
must be decided by the Courts. In areas where
the Air Pollution Authority advises the inciner-
ator designer exactly how he must design the
incinerator and exactly how he must construct
it, is the Air Pollution Authority or the designer
and builder responsible if the installation cannot
be operated at capacity and within the emission
limits ?
PA.C.ce.5. 1.66
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The Problems of Applying Incinerator Criteria
III RIGID CRITERIA
Since there is such a wide variation among
the rigid criteria adopted in various areas,
one can only assume that certain features of
such criteria are based on the whim of one
individual involved and not the combined
thinking of experienced designers. In the
East we have rigid criteria based on the as-
sumption that complete combustion of a
homogeneous mass of refuse can be obtained
in one single chamber and in the far West we
have criteria based on many tests performed
proving that multiple chambers are necessary
for complete combustion. What has happened
to the three "Ts" - temperature, time, and
turbulence - which have always been con-
sidered a must in good incinerator design?
Many articles have been written on this sub-
ject over the years confirming these points,
yet have never been disputed.
At the Air Pollution Control Association
Annual Meeting in New York in June 1961,
H. G. Meissner presented a paper from which
is quoted the first paragraph:
The three Ts of combustion, namely
"time, " "temperature, " and "turbulence"
are so closely related that they must be
considered together in determining the
performance of the incinerator. Without
time enough for the combustible matter to
burn, the desired temperature will not be
obtained, and without adequate turbulence
neither the time or temperature require-
ments will be achieved. "
At about the same time the New York City
criteria was issued with no request or pro-
visions for turbulence as a means of encour-
aging complete combustion, with complete
combustion to take place in the primary
chamber, and secondary chambers provided
for fly ash settlement only.
Reasonably high velocities and turns for the
products of combustion, or forced air in the
form of jets are the two systems most gen-
erally accepted as the means of creating tur-
bulence and mixing to promote complete com-
bustion. The former method is certainly the
more reasonable in cost and for most refuse
burning, as effective as the latter.
Under the criteria issued by Allegheny
County, Pa., the incinerator designer can-
not provide in the incinerator any zone when;
the products of combustion exceed five feet
per second. When designing an incinerator
to be built in Columbus, Ohio, the designer
must provide an area in the incinerator
where the velocity of the products of com-
bustion must reach fifty-five feet per second.
The Allegheny County criteria does not cover
the important basic design points of quantities
of theoretical and excess air nor operating
temperatures. Columbus, Ohio, on the other
hand, calls for 300% excess air and design
temperatures considerably below those ac-
ceptable to most air pollution control authori-
ties and incinerator designers.
This brings us to an even more important
weakness of a rigid criteria in which precise
dimensions and configuration of design are
outlined; namely the difficulty of differentiating
between designs for materials other than Type
1 or Type 2 Waste. Most rigid criteria which
are now in effect are based upon the burning
of normal rubbish which may contain small
quantities of garbage or other reluctantly
combustible materials. Such criteria, how-
ever, so restrict the incinerator designer
that he has difficulty in providing equipment
which he feels can handle such other wastes
as'might be collected.
The presence of a refractory hearth area
will, of course, provided for the retention
of wet materials until the moisture can be
driven off and the organic materials burned.
But in the rigid criteria the interior dimen-
sions of the incinerator are determined by
need for large volumes and great quantites
of excess air for burning Type 1 Waste and
a change is required in the criteria if proper
operation is to be achieved. It is not sufficient
to say that multiple units should be provided
each with its special design in order to take
care of its particular material since this
involves the owner in collection and selection
of waste which is at best impractical. From
experiences we know that all of these materials
are collected together and it has long been the
goal of the incinerator designer to provide
equipment which is as versatile as possible.
The modern hospital will produce large
-------
The Problems of Applying Incinerator Criteria
quantities of bulky dry waste which must, of
course, be disposed of in the incinerator.
The same hospital will, however, also pro-
duce wet garbage from the kitchen area as
well as anatomical and pathological wastes
from the laboratories and operating rooms
and possibly such materials as cage wastes
from their animal laboratories.
The incinerator design which is capable of
handling such heterogeneous materials may
vary considerably from that which has been
predetermined by the local Air Pollution
Authority as proper for incinerator design.
This same problem often arises in the field of
industry where the wastes may include Types
4, 5, and 6 in appreciable quantities. Again
the incinerator design for general rubbish may
have to be varied considerably to provide
facilities for special materials but most "rigid
criteria" have no provisions for flexibility of
design.
IV FLEXIBLE CRITERIA
From the viewpoint of the incinerator designer
or builder, the flexible criteria are by far the
more acceptable. The incinerator must, of
course, be designed within the maximum and
minimum set forth, so the inexperienced can-
not go too far afield, but the experienced de-
signer can apply his knowledge and experience
to both design and construction. Most im-
portant of all, however, is that he, the
designer and constructor, is held responsible
for his design. This the architect, engineer,
and owner want and this the responsible de-
signer is willing to accept.
In metropolitan areas around the country, it
is becoming increasingly important that cri-
teria in one form, or another be established in
order that the engineer and/or architect can
properly plan the waste disposal equipment
and its space requirements. A modern hos-
pital or laboratory facility is designed in such
a way that no waste space is provided and each
and every factor in its operation must be care-
fully planned. The incinerator designer is con-
stantly being asked to make recommendations
upon which space allocations can be established
and which in turn will determine what stack
facilities, utility services, etc., must be
provided. They cannot wait until a general
contractor has been established and he in
turn has determined all of his subcontractors,
including the incinerator contractor, in order
to determine what will be acceptable in the
way of incincerator facilities for their various
waste materials.
Neither can the incinerator designer provide
the necessary data to allow a formal application
to be presented to the local Air Pollution Authori-
ties. This then leaves the absolute necessity of
establishing acceptable limits of design based
not only on Type 1 Waste materials but on the
anticipated character of wastes whatever they
may be. It further necessitates an approach
by Air Pollution Authorities which will allow
the incinerator designer prior knowledge as
to the acceptability of a special design. A
flexible criteria augmented by a practical
means of confirming operation within accept-
able limits would, therefore, leave the in-
cinerator designer free to make proper
recommendations, based upon his experiences,
to archietects or engineers with the assurance
that these recommendations would be accept-
able to the local authorities.
If after such an installation were made,
criticism is then leveled at the owner for
the operation of his equipment, there is no
question of responsibility since it lies entirely
with the incinerator designer and he must
make whatever changes are necessary to
comply with the local ordinances.
As outlined above, the use of flexible criteria
does indeed place the responsibility for the
design upon the incinerator engineer. It
further points up the need for an economical,
visual, and practical test of the operation of
such equipment in order to prove compliance
with the local ordinances as they apply to
stack emissions.
V INCINERATOR STANDARDS OF 1.1. A.
It is the sincere belief of the members of the
Incinerator Institute of America that the In-
cinerator Standards of April 1963, its fifth
published version, outlines the basis for
good incinerator design. The Standards are
in sufficient detail, yet flexible enough to
-------
The Problems of Applying Incinerator Criteria
allow the designer leeway in providing for
any type of waste, and not restrictive to
meritorious improvements.
The requests for copies is definite proof of
its popularity and, since more and more com-
munities are adopting it, in whole or in part,
as their incinerator criteria, it is further
proof of its reasonable approach to good in-
cinerator design.
It is interesting to note that one of the Incin-
erator Institute members, Joseph Coder
Incinerator Company, has constructed and
tested three incinerators one designed on the
basis of the 1.1. A. Standards, another based
on the Los Angeles criteria and the third
based on the New York City criteria. The
results of the tests, conducted by a recognized
testing laboratory, are available through 1.1.
A. and show that the incinerator designed ac-
cording to the 1.1. A. Standards is as efficient
as the other two. If the efficiency of operation
is compared to construction costs, the I.I. A.
design was approximately 20% more efficient
than the Los Angeles design and approximately
100% more efficient than the New York City
design.
In comparing the criteria published by the
various Air Pollution Control Authorities
with the Incinerator Institute Standards, there
appears to be no disagreement with the fol-
lowing portions of the 1.1. A. Standards:
A Definitions
B Waste Analysis
C Classification of Incinerators
D Specifications of Incinerators by Classes
E Cast iron and hearth area requirements
for the burning of solid refuse. (Although
there appears to be some minor disagree-
ments on the use of hearth areas and the
proportion of one to the other and the pro-
portion of length versus width, it must be
remembered that the areas stipulated in
the Institute Standards are minimum and
can be increased at the discretion of the
incinerator designer.)
F Auxiliary burner capacity
The points of disagreement might be listed
as follows:
1 Furnace volume: The point of dis-
agreement on this subject appears to
center more on whether complete com-
bustion takes place entirely in the pri-
mary chamber or continues after
turbulence has been provided.
2 "Time, " "temperature, " and "turbu-
lence": These we do not believe arc
actual subjects of disagreements but
rather oversights in many of the criteria
being issued. Apparently Allegheny
County recognizes this and now permits
a higher velocity than five feet per
second in the first gas port. Columbus,
Ohio, on the other hand, have apparently
concluded the 55 feet per second for
velocity is excessive and they now per-
mit a 20% reduction on all sizes of in-
cinerator and as much as 85% reduction
on units with a capacity of 100 Ibs per
hour or less.
3 Amounts of excess air to be used in
calculations: This again appears to be
an oversight not to have included the
requirement in the criteria rather
than a disagreement. The Institute
Standards require 100% excess air,
New York City speaks of 200% but
actually uses 100%, whereas Columbus,
Ohio, requires 300% with a resultant
lower furnace temperature.
4 Velocity reduction required to settle
out fly-ash.
To give you a visual comparison of inciner-
ators based on published criteria and stand-
ards, there is shown below five designs.
Each incinerator shown has a rated capacity
of 1000 Ibs hour of Type 1 Waste.
All of the figures are drawn to scale with
1/4 inch equal to one foot, and "A" indicating
location of secondary air inlet and "B" the
auxiliary gas burner.
-------
The Problems of Applying Incineratpr Criteriii
When using the 1.1. A. Standards, the exact
locations of secondary air inlets and auxiliary
burner are determined by the incinerator
designer.
Furnaces in Figs. 1, 2, and 3 have an in-
ternal width of five feet and furnaces shown
in Figs. 4 and 5, an internal width of four
feet six inches.
C I!
Fie. i.
fie. 3.
'-,-.._
t
1
s
^v
1
^.
\
vvV.v.v V. .. ,-^v,
S^^^SS VVS
rr
p H U
^Isssssss^-
-rr-
r"
\
SSSSK
Fig. 4.
r 'r~^s
,;
v^
\
M
tN
Fig. i.
REFERENCE
1 A.P.C.A. Publication, Vol. 14, No. 9,
Sept. 1964. pp 363-365.
l-.l
Fie. 3.
-------
DISCUSSION OF"THE PROBLEMS OF APPLYING
INCINERATOR CRITERIA"
H.G. Meissner* and H. C. Johnson**
The author discourses at considerable length
on the relative merits of "flexible" vs. "rigid"
criteria, without defining either term. He
acknowledges that there must be maximum
and minimum values, so that the "inexperi-
enced cannot go too far afield, but the experi-
enced designer can apply his knowledge and
experience to both design and construction. "
Unfortunately there seems to be more inex-
perienced than experienced incinerator de-
signers, at least in this territory.
Criteria are in many ways similar to building
codes and specifications, in that they set up
standards that will be acceptable, so that
designers will know beforehand what to ex-
pect and how to plan. When the criteria are
too flexible, the examiners personal opinion
may decide approval or disapproval. The IIA
Standards are in some respects inadequate
for this reason, as H.C. Johnson notes in
his discussion. We have found in checking
various incinerator manufacturer catalogs,
as much as 100% variation in sizing for the
same capacity. In one test, the incinerator
could not burn more than 25% of its rated
capacity, yet we have been asked v/hy we con-
sider the refuse burning rate such an impor-
tant factor.
Basing approval entirely on test results may
be satisfactory where the number of incinera-
tors is limited, but would place an impossible
burden on both parties, where hundreds of
applications are filed yearly, many of which
would have to be tested to prove compliance.
At present we know of no "economical, visual,
and practical test of the operation of such
equipment in order to prove compliance with
the local ordinances, as they apply to stack
emissions, " which the author suggests is
desirable.
The New York City Criteria state that "in
order to preclude prohibition of meritorious
improvements not in compliance with these
Criteria, the Commissioner may consider
alternate designs. Experimental or temporary
permits may then be issued, with final approval
when and if the incinerators are found to
operate satisfactorily. "
The so-called tests run on three designs of
incinerators by the Joseph Coder Incinerator
Company, were of such short duration, and
under such unfavorable operating conditions
of draft, etc., that the results would be con-
sidered unsatisfactory for all three designs.
The author's comparison of efficiency of opera-
tion with construction costs, to show that one
design is 100% more efficient than another, is
novel but totally unacceptable to a control
agency, as this would favor a poor design just
because it was cheap.
This paper would be of more value if the author
had been more specific in what he wants. Re-
peated reference to the IIA Standards, which
are in themselves not too specific, leaves the
reader wondering just what Criteria the author
would favor. *
^Assistant Director of Engineering, Department
of Air Pollution Control, New York, N.Y.
This paper questions the role of air pollution
control agencies in setting incinerator design
standards. It infers that the design standards.
set up by the Incinerator Institute of America
should be adopted in preference to any other
Standards. I believe that most air pollution
authorities would be willing to accept the
standards of some organization such as IIA,
the APCA, or the ASME, if they could be
assured that adoption of such standards would
result in satisfactory incineration in their arr-a.
The question to be answered then is what
standards will provide incinerators which in
actual day-to-day operation, will discharge
the least amount of objectionable materials into
the atmosphere, and provide the lowest total
cost of incineration?
PA.C. ce. 6. 1.66
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Discussion of "The Problems of Applying Incinerator Criteria'
Diagrams of four basic designs are presented
tests on three of these are mentioned. The
apparent similarity between the Los Angeles
and IIA diagrams in this paper is misleading.
The IIA Standards as presently written allow
wide variations in design not shown or men-
tioned in the paper. No test data or stack
observations have been presented to show the
effect of these many possible design variables
on emissions. Intelligent analysis of these
design standards cannot be made until an
extensive test program has been carried out
on all of the possible incinerator designs
under these standards. Before such a testing
program is carried out, agreement should
be reached on test methods, types of material
to be burned, and operating procedures dur-
ing the tests. The test results will not be
representative of actual emissions from in-
cinerators unless the materials burned re-
present the usual type of refuse to be burned,
and incinerators are operated in the normal
manner to be expected by the majority of
operators. Most operators and owners dis-
play little interest in their incinerator, there-
fore, it must be designed to be as foolproof
as possible. An incinerator must be capable
of burning a wide variety of refuse charged
in varying amounts and varying cycles with-
out violating air pollution requirements.
Under these adverse operating conditions,
we have found the Los Angeles design dis-
charges less visible plume, particulate, and
combustibles than other designs observed or
tested in this area. Los Angeles engineers
have supplied design data for several special
designs which have not yet been published;
this includes pathological, insulation burners,
and wood waste burners.
The Los Angeles multiple chamber incinera-
tor admittedly is an expensive design, but
the statement that the IIA design is 20%
cheaper than the Los Angeles design needs
clarification. This difference represents the
difference in burning rate per square feet of
grate between IIA and Los Angeles publica-
tions. Burning rate tests have been conducted
by this District on Los Angeles and IIA de-
signs. Very little difference in burning rate
per square feet of grate per hour were noted.
In fact, under normal operating conditions,
burning rates were considerably below either
the Los Angeles or IIA ratings. Therefore,
if incinerators arn given a nominal rating that
can be normally achieved, the first cost should
be compared on the basis of square feet of
grate area. When put on this basis, the cost
of the Los Angeles and IIA design are not far
apart according to the representatives of the
Bay Area Incinerator Industry.
We have had no experience with the New York
Allegheny County designs, and have received
no test data on these units. However, our
experience with the Los Angeles design indi-
cates that while some improvement in fly ash
emission may have been achieved with these
designs, all other emissions could be expected
to be considerably higher. The emission of
fly ash is prohibited in this District if it falls
on the property of others and causes an annoy-
ance. The few complaints received have been
completely solved only by the installation of
some type of water spray chambers. No
baffle chambers have been tried, but settling
chambers have not proved effective in pre-
venting the emission of paper ash containing
essentially no combustibles.
The question of flexible vs. rigid criteria
should also be considered. This District de-
pends entirely on emission standards, com-
pliance being determined by tests and plume
observations. The West Coast Incinerator
Industry has standardized on the Los Angeles
designs, which have been quite satisfactory
in this area. However, several special de-
signs have been installed to fit into existing
space, which could lead to new designs to
reduce cost or achieve other desired
characteristics. **
**Senior Air Pollution Engineer, Bay Area
APCD, San Francisco, California.
REFERENCE
1 APCA publication, Vol. 14, No. 9, pp.
366-377. September, 1964.
-------
COMBUSTION AND HEAT CALCULATIONS
FOR INCINERATORS
Elmer R. Kaiser*
I ABSTRACT
The design of industrial and municipal incin-
erators is based on combustion and heat con-
siderations. The procedures are given for
calculating the quantities of air, flue gas,
water and heat, as well as the gas temper-
atures. To assist the reader, a municipal
incinerator is used as an example. The re-
lation between refuse analysis and flue gas
analysis is explained. Sections on dry and
wet dust collection are included.
II INTRODUCTION
Incineration is a combustion process which
today is becoming more technical and
scientific. More understanding of the process
through quantitative measurement and analysis
will surely aid in developing the incinerator
art as it has similar arts, such as steam gen-
eration and gas manufacture.
Coupled with experience factors and valid
assumptions, combustion and heat calculations
are invaluable in designing an incinerator and
in evaluating its performance. The sizing of
furnaces, gas passages, dust collectors,
fans and stacks are based on expectations de-
duced with the help of combustion and thermal
data.
The purpose of this paper is to provide some
of the methods and formulas for establishing
the relationships between the quantities of
air, refuse, residue, water and fly ash, as
well as the heat and material balances. When
the flow sheet and temperatures have thus
been established for a given incinerator, the
engineer can size the equipment. The latter
subject includes many experience factors be-
yond the scope of this paper.
The methods and procedures that will be help-
full shall be presented for a hypothetical in-
cinerator and refuse. Data which will be
assumed are close to those for actual in-
cinerators and refuse, but are intended for
illustration only. In actual designs the reader
is advised to use data that apply to the designs.
The calculations are presented in a basic form
for clarity and for the precision necessary for
heat and material balances. Short cuts are
possible and desirable, especially for any
specific type of incinerator. Nomograms
graphs, tables and special factors are avail-
able elsewhere or may be prepared by the
reader. However, one frequently returns to
the fundamental relationships and should retain
facility with them. The weight method of com-
bustion calculation is used in this paper rather
than the mole method. Both methods are ex-
plained in the 37th edition of "Steam". < 1)
III EXAMPLE INCINERATOR
A hypothetical municipal incinerator furnace
is assumed which has continuous charging,
24-hr a day, and continuous residue discharge.
A Rated Capacity
Usually expressed as tons per 24-hr,
the rated capacity of this incinerator is
240 tons. The hourly charging rate is
10 tons or 20, 000 Ib of refuse.
B Grate Loading - Firing Rates
Assume the grate had a projected plan
area of 333 sq ft. The firing rate = 20, OOO/
333 = 60 Ib per sq ft-hr.
C Furnace Volumes - Combustion Chamber
Volume
Assume the primary furnace has a volume
above the grates of 31. 2 cu ft per ton of
rated capacity, the furnace volume is
31.2 (240) = 7500 cu ft.
*Senior Research Scientist, New York University, New York, New"Tork7
Proceedings of the 1964 National Incinerator Conference.
PA.C.ce.23. 9.66
Published in the
-------
Combustion and Heat Calculations for Incinerators
A combustion chamber usually follows the
furnace and has the purpose of completing
combustion of the gases and suspended
particles, as well as trapping some of the
fly ash. Volumes range up to 2.4 times
the furnace volume. '2) in Some cases
the primary furnace discharges its gases
into a spray chamber where water quenches
combustion and traps particulates matter^3)
For the present purpose, one may assume
complete combustion of the gases but allow
4 per cent unburned carbon in the total
residue.
D Heat Release Rates
The higher heating value of the refuse is
assumed at 4230 Btu/lb as fired. The nominal
heat release per cu ft of furnace volume is
20,000(4230/7500 = 11, 280 Btu/cu ft-hr. Be-
cause of unburned carbon in the residue, the
actual heat release rate is 10, 890 Btu/cu
ft-hr.
E Gas Cleaning
Because of the carry-over of fly ash from
the furnace and combustion chamber, and
alternative possibilities for cleaning the
gases, calculations will be presented for
the furnace and combustion chamber in
combination with:
1 A spray chamber followed by a dry-type
dust separator, ID fan and stack.
2 A gas scrubber, ED fan and stack.
Hence, the hypothetical incinerator con-
sists essentially of a furnace with con-
tinuous charging, a combustion chamber,
a spray chamber for partially cooling the
gases and trapping some fly ash, one of
several methods of collecting dust, an
induced-draft fan and stack.
Steady-state operation is assumed at
rated capacity.
Moisture
Carbon
Hydrogen
Oxygen
Nitrogen
Sulfur
Non-combustibles'
Per cent
30.00
22.95
3. 25
18. 80
negl.
negl.
25.00
100.00
The net hydrogen ( H) available for com-
bustion is 3.25 - (18.80/8) = 0.90 per
cent. The bound water in the above re-
fuse, which is released during combustion,
is 18. 80(9/8) = 21. 15 per cent of the
residue.
In essence, the dry combustible matter
consists in this case of 4 parts of cellulose,
starch and sugar (CgH10O5) and 1 part of
a mixture of proteins, fats, oils, waxes,
rubber, plastics, etc. The main con-
stituent is cellulose, which like starch and
sugar has the following makeup:
Carbon
Net hydrogen,
(H)
Moisture (bound
water)
Per cent
44.4
0.0
55.6
100.0
Approximate
higher
heating value
(HHV):
7500 Btu/lb(4)
The mixture of proteins, fats, oils, etc.
has, for practical purposes, the following
composition:
Carbon
Per cent
77.4
Net hydrogen, 10.0
(H)
Moisture (bound 12. 6
water) JOO. 0
Approximate
higher
heating value
(HHV):
17, 000 Btu/lb
IV BASIC ASSUMPTIONS
A Refuse
The charging rate is assumed at 20, 000 Ib
an hr of refuse consisting of:
*Non-combustibles include ash, glass, ceramics,
mineral dirt and metals. The latter are partial-
ly oxidized, release heat, and increase in
weight. The design calculations for the burn-
ing of the metals may be neglected in this
case.
-------
Combustion atid Heat Calculations for Incinerators
Nitrogen is about 0. 3 per cent and sulfur
is be.'ow 0. 2 per cent of municipal refuse.
They are not included in these calculations.
By arithmetic, the HHV of the combined
refuse is:
4(7.500) .(17.000) (0.45)B4230Btu/lb.
B Air
To prevent furnace temperatures high
enough to cause slag to run down the
furnace walls, enough air is supplied to
control the temperature of the furnace
exit gases at 1600 - 1800°F. As a first
approximation, the air to the grate and
furnace is 2. 3 times the stoichiometric
air requirement, or 130 per cent excess
air. The air is supplied at 80°F and 30
in. Hg barometer. The air contains
0.0132 Ib water vapor per Ib dry air. The
air, refuse, and water for sprays are all
assumed to be at 80°F. At any specific
location a different set of conditions may
be assumed.
C Residue and Fly Ash
The total solid residue is assumed to con-
tain 4 per cent carbon. All of the unburned
carbon is assumed to remain in the grate
residue, although in actual practice some
is lost in the stack gases. The residue
from the grate is cooled from 1200°F to
150°F by spraying with water or dropped
into water before removal from the ash
pit. The water vapor produced joins the
furnace gases. The carry-over of solids
with the furnace exit gases is assumed at
40 Ib/ton of refuse, or 400 Ib per hr.
D Other Assumptions
The heat loss through the furnace and com-
bustion chamber walls is assumed at
1, 800, 000 Btu/hr (Btuh). The heat losses
through the walls of other equipment ahead
of the ID fan will be assumed and stated
in the calculations. The heat losses
through the walls can be predicted reason-
ably well from thermal conductivities of
the refractory and insulation.
Alternate methods of tempering the
furnace exit gases in preparation for
dust collection will be considered in turn.
Only two of many types of dust separators
are considered. The ultimate objective is
to clean the gases to legal limits, which
vary with communities from about 1.0 to
0.4 Ib per 1000 Ib of flue gas, corrected
to 50 per cent excess air.
Among the many questions to be answered
by calculation are:
1 How much air does the furnace require?
2 What is the flue-gas analysis?
3 What is the actual cfm flowing from the
furnace to the spray chamber? From
the spray chamber?
4 How much water is required for the
spray chamber? For a gas scrubber?
5 What is the saturation temperature of
the flue gas, an index to white fog plume
from the stack?
6 How can the fog plume from a scrubber
be prevented ?
7 What is the dust loading of the stack
gases, corrected to 50 per cent excess
air?
V COMBUSTION CALCULATIONS
A Refuse
For combustion purposes the refuse may
be restated in the following form:
-------
Combustion and Heat Calculations for Incinerators
Carbon: (0. 2295)(20, 000)
Less C in residue: (0. 04)(0. 24)(20, 000)(0. 96)
Available hydrogen: (0.009) (20,000)
Moisture, initial: (0.30) (20,000)
bound water (0.2115) (20,000)
Residue, all forms
Ash, metal, glass: (0.25) (20,000)
Carbon
= 4, 590
208
= 6,000
= 4,230
= 5, 000
208
Hourly total
4, 382
180
10, 230
5.208
20, 000 Ib
B Combustion
We are now ready to analyze the combus-
tion process in more detail. The first
question to answer is: How much theoretical
or stoichiometric air is required to burn
the carbon and available hydrogen gasified ?
The stoichiometric proportions are:
1 Ib carbon requires 11. 53 Ib air to pro-
duce 3. 665 Ib of carbon dioxide and 8. 865
Ib nitrogen. 1 Ib hydrogen requires 34.34
Ib air to produce 8. 936 Ib of water vapor
and 26.404 Ib nitrogen.
The dry air theoretically required for com-
bustion of the refuse actually burned is
For the carbon: 4382 (11. 53) = 50, 524 Ib
For the available hydrogen: = 6, 181
180(34.34)
Theoretical dry air, = 56, 705 Ib
hourly
Excess air = 1. SOX 56, 705 = 13, 717
Total dry air per hr = 130, 422 Ib
The calculations are carried beyond the
usual 3 or 4 significant figures to reduce
adjustment later in the heat and material
balances.
Dry air consists of 23. 15 per cent oxygen
and 76. 85 per cent nitrogen by weight,
and 20. 9 per cent oxygen and 79. 1 per
cent nitrogen by volume. Some engineers
use 21.0 and 79.0 per cent, respectively,
for the volumes. As outdoor air contains
moisture, it is standard practice in com-
bustion calculations for boilers to add
0.0132 Ib of moisture per Ib of dry air.
This value corresponds to 60 per cent
relative humidity at 80°F dry bulb
temperature.
The water vapor produced in quenching
the grate residue is added to the furnace
gas. The dry grate residue is 5208 -
400 = 4808 Ib. Sp. ht. = 0.25. The heat
liberated by residue = 4808(0.25) (1200 -
150) = 1,262,000 Btu. Approximate heat
gained by each Ib of quench water
evaporated;
1150 - 48 = 1102 Btu/lb
Lb water evaporated = 1,262,000/1102
= 11451b/hrto
quench grate
residue.
At this point it is advisable to summarize
the weights in the form of a material
balance. The tabulation provides an over-
all view of the process, and assists in
tracking down errors in calculations as
input must equal output. Table 1 is based
on the calculations for the example
incinerator.
C Flue-Gas Composition
Assuming complete combustion, if the
flue gases that leave the combustion chamber
were sampled and analyzed by Or sat
apparatus, the following analysis would
be obtained:
-------
Combustion and Heat Calculations for Incinerators
TABLE I
MATERIAL BALANCE FOR FURNACE
AND COMBUSTION CHAMBER
Input
R«fuie
Dry air
Air moisturft
Quench wa'f
Lb/hr
20,000
130,472
1.722
1.145
Totol, hourly 153,289 Ib
Ju tpot
O'v )lu« goi
123.375
CO,
0,.
H,.
Wo..r
(rom
•r'.m
from
''Of,
."-rcfff
C a-rv
Gat
CO,
o,
CO
N,
: 4382 (3.6C5)
. 110,422(1.30/2.
i 30. 422 O. 7685)
vnpor
rflfuie
dir (130 J4/i{0.0
16,073
301(0.2315) 17,073
100,229
10,230
"(21 1,722
14,706
corrb-ilt.on o( (HI, (180)(8.936) 1,609
ash pit
tn s idu*
ovo- 10! idi
Wgt, Ib
16,073
17,073
0
100,229
133,375
1, 14.S
Totol, hourly
Cu ff/lb* Cu ft*
8.548 137,390
11.819 201,786
13.506 0
13.443 1,347,378
1,686,554
4.306
400
153,289 Ib
Orsdt, dry
vol. p«r cent
8.15
11.96
0.0
79.89
100.00
Lb C +(H) = _
Lb air
18. 3N_
= 0^528 (79.89) +4(8. 15) - 2(11.96) + 5(0. 0)
18.3(79.89)
= 0.0348.
The reciprocal,
Lb air l
Lb C + (H) Lb~C
air = 0.0348 = 28' 7'
which checks Jf-+^_ a 28.6
from the weights of carbon burned and the
net hydrogen.
When cellulose, starch, sugar or carbon
are burned completely, alone or in any
combination, the Orsat readings of CO2
and O2 total 20. 9 per cent. When some
available hydrogen is present, the total of
CO2 and O2 is reduced, while nitrogen in-
creases above 79. 1 per cent. If the C:(H)
ratio of the fuel burned is not known, it
may be calculated from the Orsat analysis,
thus:
If we did not know the percentage excess
air, we could calculate it from the analysis
of the flue gases by substituting gas volume
percentages in the following equation:
Excess air, per cent = 100 x
0, - CO/2
0.264/Y, - (0, - CO/2)
1196
0.264(79.89) - 11.96
1196 1196
-= 131%
21.09-11.96 9.13
a good check on 130 per cent originally
assumed.
From the Orsat data one can also determine
the Ib air/lb C + (H) and the Ib C + (H) per
Ib air.
C:(H) ratio
CO,,
8.80 - 0.421 (CO ~+0_)
£ 2
8. 15
8.80 - 0.421 (8. 15 + 11.96)
24.4.
*At 60°F, 30 in. Hg abs. press. The water
vapor is not measured by Orsat, but would
be determined by condensing the moisture from
a measured volume of flue gas. Incidently, the
Orsat apparatus measures only to 0. 1 per cent.
A series of readings without error must be
averaged to obtain significant values beyond
0. 1 per cent.
-------
Combustion and Heat Calculations for Incinerators
The actual ratio was
4382
180
= 24.4 ck. If
all the carbon had been burned, the ratio
4590
would have been = 25.5.
VI HEAT CALCULATIONS
A Furnace and Combustion Chamber
The heat input is the heating value of the
refuse, to which should be added the heat
of vaporization of the air moisture as all
other water is initially in the liquid state.
The base temperature is 80°F.
Refuse: 20,000(4230) 84,600,000
Air moisture: 1,722(1048.6) 1,805.690
Total heat input
86,405,690
Btuh.
The known heat losses from the furnace
include:
1) Sensible heat in carry-over solids at
an estimated 1630°F; sp. ht. of ash
assumed at 0. 25.
400(0.25) (1630-80) =
155,000 Btuh.
2) Sensible heat in quenched grate residue,
4808(0.25) (150-80) = 84,140
3) Sensible heat lost through furnace and
combustion chamber enclosure
1. 800, 000
4) Latent chemical heat of the carbon in
the residue:
208(14,093) =
2.931. 340
4,970, 480 Btuh
The heat of vaporization at 80°F for
moisture in the flue gas is 14, 706 (1048.6)
= 15.420, 710 Btuh. The heat remaining
for superheating gases and vapor above
80°F is
As the resultant gas temperature is to be
read off Figure 1, we must first establish
the moisture content of the gases in per
cent of the flue gas, thus:
14,706
133, 375 + 14. 706
= 9. 85% moisture by
weight of total flue
gas.
The enthalpy of the flue gas above 80 F,
with all moisture in vapor form is
66,014, 500
133, 375 + 14, 706
= 446 Btu/lb.
Figure 1 indicates a gas temperature of 1630°F
at the combustion-chamber exit; hence the
assumed temperature is correct. The wall
andarchtemperatures in the furnace would
probably be slightly hotter in the zone closest
to the hottest flames. Slag deposition and run-
ning onthe walls is experienced above 1800°F.
The assumed conditions and exit gas temper-
ature are in the range of good practice. The
temperature can be increased by decreasing
the amount of excess air entering the furnace.
The heat balance for the furnace and com-
bustion chamber, Table 2, can be com-
pleted with the aid of steam tables. It is
not necessary to achieve a perfect balance;
minor differences may be carried as "un-
accounted for. "
VII SPRAY CHAMBER
When the furnace gases are to be cleaned by
a cyclonic, electrostatic or other dry dust
collector, the gases must be cooled or tem-
pered. A waste heat boiler would accomplish
the result, or water sprays with or without
additional ambient air could be used. The
objective in this example is to cool the furnace
gases to 600°F by adding air and water in a
chamber following immediately after the com-
bustion chamber. Water sprays alone could
do the job but the addition of air is a practical
86, 405, 690 - 4, 970, 480 - 15, 420, 710 = 66, 014, 500 Btuh.
Bur-
*Resultant of successive approximations of
exit gas termperature from bustion chamber.
The correct temperature assumed must finally
equal the temperature obtained from Figure 1.
-------
Combustion and Heat Calculations for Incinerators
TEMPERATURE, F.
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TEMPFRATURE, F.
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FIO. I. ENTHALPY OF FLUF GAS ABOVF RO F.
aid in the protection of refractories and in
temperature control.
The additional air bled into the example spray
chamber, including leakage, assumed at
50, 000 Ib/hr, consists of 49, 350 dry air and
650 Ib air moisture. Heat lost through the
walls is 1, 200. 000 Btuh. The amount of spray
water needed is that quantity which will absorb
the excess of heat above 600°F after the
other losses have been deducted. Each Ib of
spray vvater evaporated will absorb 1334. 8 -
48. 0 or 1286. 8 Btu. To sluice ash out of the
spray chamber 10 gpm of water is added. The
ash trapped is assumed a 175 Ib per hr. As
the available heat for the sprays can be cal-
culated by difference, we prepare the heat
balance for the spray chamber, Table 3.
-------
Combustion and Heat Calculations for Incinerators
Table 2. HOURLY HEAT BALANCE FOR FURNACE AND
COMBUSTION CHAMBER HEATS ABOVE 80°F
Input Btuh Per cent
HeatmR vtiluc of rt- fusi- 84. 600, 000 97. 9
20.000 (4230)
Latent heat of air moisture 1. 805. 690 2. 1
Total 86, 405. 690 100. 0
Outfmt
Sensible heat of dry gas at 1630°F
133. 375 (408) - from Fig. 1 54, 417, 000 63. 0
Sensible and Latent heat In water
vapor 14,706(1874-48) • from
steam tables 26, 882. 568 31.1
Sensible heat in dust carry-over
400 (0.25) (1630-80) 155.000 0.2
Sensible heat in grate residue
4808 (0. 25) ( 150-80) 84, 140 0. 1
Sensible heat loss through wallg 1. 800, 000 2. 1
Chemical heat of carbon in residue
(14,093) (208) 2,931. 340 3.4
Unaccounted for 135, 642 0. 1
Total 86,405.690 100.0
Table 3. HOURLY HEAT BALANCE KOK
SPH.AY CHAMFIEH UK ATS ABOVE B0°l'
Input at I630°F Btuh
Sensible heat of dry gas from furnace 54, 417, 000
Sensible and latent heat in water vapor from
furnace 26, B82, 5GB
Sensible heal in carry-over • • - 155,000
Unaccounted for heat from furnace 135, 642
Latent heat of moisture in bleed air -
(104B.6) (650) 681, 590
Toial 82, 271. 000
Output at 600 F
Sensible heat m dry gas: (49. 350 + 133, 375)
(128) - Fig. 1 23,388, BOO
(600-80) 29.250
Sensible und latent heat in bleed air
moisture 650 (1334. 8 - 48.0) 83$, 420
Sensible heat in sluice water at 150°F: 349, 860
10 (8.33) 60 (110-80)
In sluice ash, 175(0.25)1150-80) 3,063
Sensible and latent heat in vapor from furnace
and spray water, by difference:
43,880(1331.8-48.0) 56,464,407
Total 82. 271, 800
The amount of evaporated spray water is
43, 800 - G50 - 14. 70C " 28, 524 Ib/hr. or
57 0 fpm. The sluice water Is an additional 10 gpm.
All of the data are now available for Table 4,
the material balance of the spray chamber,
which should now be prepared. The material
balance for the furnace and combustion chamber
provides much of the data needed.
TABLE 4
HOURLY MATERIAL BALANCE FOR SPRAY CHAMBER
'"Put Lb/hr
Dry 901*1 from com bullion chamber 133,375
Carbon dioiid* 16,07)
Oiygon 17,073
Nilraaon 100,229
Dry blood oir 49,350
Wotor vapor: 15,356
In blood air 650
Wotor lupply: 33,522
To .pray, (ovaporatod) 28,524
To iluico 4,998
Fly o.h 400
Total 232,003
Output
Dry ,0101: 182,725
Corbon die, id. 16,073
O.yo.n 17,073+0.2315(49,350) 28,498
Nitrogon 100,229+0.7685(49,350) 138.154
Wotor vapor: 28,524+15.356 43,880
Sluico orator: 10 gpm 4,991
Trapped fly ath 175
Fly Ofh in goiot 225
Totol 232,003
182,7?5
Stream fog occurs when the mixture is cooled
below the saturation temperature. (5)
The Orsat analysis of the gas leaving the spray
chamber would show the composition below if
no CO? is absorbed by the water or ash. Con-
flicting data exist on the latter point.
.j. D'y »ol.
Cot Wgt Cu It/lb^ Cu ft por cont
CO, 16,073 8.548 137,390 5.89
0, 28,498 11.819 336,818 14.44
N, 138,154 13.443 1,857,204 79.67
2,331,412 100.00
Note that the C:(H) ratio is 24.4 aa before:
5.89
C'fH) ratio - - "4 4
"""' 8.80-0.421(5.89+14.44)
If CC>2 is absorbed in the spray chamber, the
sum of CO9 and O2 will decrease and the C:(H)
ratio will not match that of the original com-
*At 60°F, 30 in. Hg. abs. pressure.
bustible burned.
-------
Combustion and Heat Calculations for Incinerators
The final per cent excess air =
1444
100(0.)
0.264/V, - 0,
1444
0.264(79.67)-14.44 21.03-14.44
= 216 per cent,
which compares with the per cent excess air by weight:
Total air-Theoretical air 130,422 * 49,350 - 56,705
Theoretical air
56,705
2.17 or 217 percent clc.
VIII COMBINED PROCESS
The result obtained by the furnace, combustion
chamber, and spray chamber may be compared
with the total input by a Process Materials
Balance and Process Heat Balance. For this
purpose the process is ended at the discharge
from the spray chamber. However, process
balances can also be prepared to include later
stages if desired.
TABLES
PROCESS MATERIAL BALANCE —FURNACE.
COMBUSTION, AND SPRAY CHAMBERS
Input
Refute, at fired
Dry Air
Air moittgre at 0.013] Ib/lb air
Qu*nch and tluice wattr, 69.3 gpm
Total input, Ib
Output
Dry flu* got:
CO, 16,073
0, 28,498
N, 138.154
Water vapor
Rotidue: Grot*
Fly Ath
Sproychambar flurry
Water 4,998
Solidt 175
Lb/hr
20,000
179,772
J.372
34,667
236,811
182.725
43,880
4.808
225
5,173
Total output, Ib 236,811
If additional water is required for wetting and
transporting residue, this extra water does
not affect the combustion and heat calculations.
IX DUST LOADING OF STACK GASES —
DRY COLLECTOR
The spray chamber tempers the gases to 600°F
but discharges 225 Ib of fly ash per hr mixed
TABLE b
PROCESS HEAT BALANCE —FURNACE,
COMBUSTION, AND SPRAY CHAMBERS
Input
Btu/hr
Heating value (HHV) of ref
4230 Btu/lb
ute,
Latent heat of air moiitura,
2372 (1048.6)
Total, hou'ly
Output
Sintibl* and lot
water vapor at
Sent ibU h*Ot in
and tolidt at 1
Sensible h«at in
150F
Sent ible heat in
S«n»ibl« heat lo
• nt h»ot in
600 F
I50F
600F
84
2
87
23
57
grata rasidua o1
fly oth at
• t through
Chemicol h»ot in unburnod
600F
wolll
carbon
3
2
,600,
,487,
,087,
,388,
,300,
352,
84,
29,
,000,
,931,
000
280
280
800
967
923
140
250
000
000
200
Per cent
97.
2,
100,
26,
65.
0,
o,
3
3,
2
6
,0
,8
9
,4
,1
.4
4
Total, hourly
Roughly two-third* of the h»ot in ttv
vapor, ona-fourth to dry gai ond tha
athar lo«t*t.
87,087,260 100.0
I r*futa it lott to wOt*r
remaining twelfth to all
with 226, 605 Ib of flue gas. Incinerator fly
ash is not easy to catch mechanically, because
it readily degrades to fine powder. Neverthe-
less, methods are available which have a
wide range of efficiency. By way of illustra-
tion, we may assume a dry dust separator of
60 per cent collection efficiency. Hence,
90 Ib of dust per hr is emitted out the stack.
What is the magnitude of this emission in
relation to the oft-accepted standard limit
of 0. 85 Ib per 1000 Ib flue gas, corrected to
50 percent excess air1*6'
The actual emission is 90/226. 605 = 0. 397 Ib
per 1000 Ib flue gas. By sampling the stack
gases one would establish the dust loading as
well as the 216 per cent excess air (by Orsat)
and the moisture content of the flue gas. The
amount of spray water evaporated would not
normally be determined, nor would the moisture
content of the refuse be known.
tent of the flue gas is 5. 89 per cent, dry"
volume.
The CO2 con-
It is common practice to assume that 50 per
cent, excess air corresponds to 12 per cent
CO2 volume in the dry flue gas. If this assump-
tion is accepted, the corrected dust loading is
0. 396 X 12/5.89 = 0. 809 lb/1000 Ib of corrected
flue gas.
-------
Combustion and Heat Calculations for Incinerators
The validity of this assumption and resultant
calculation can be compared with the actual
flue gas corrected to 50 per cent excess air
in the example case. The total air supplied
was 179, 772 Ib at 217 per cent excess air.
At 50 per cent excess air, the total air would
have been 179, 772 (1. 50/3. 17) = 85, 065 Ib/hr.
The flue gas would be 226, 605 - (179, 772 -
85, 065) = 131, 898 Ib/hr at 50 per cent excess
air. The corrected dust loading on the weight
basis would be 0. 397 X226, 605/131, 898 =
0.683 Ib per 1000 Ib flue gas.
If the evaporated spray water is also deter-
mined and deducted as dilution of the stack
gases, the corrected weight of flue gas at 50
per cent excess air would be 131, 898-28, 524 =
103, 374 Ib per hr. The corrected dust loading
on this basis would be 0. 397 X 226, 605/103, 374
= 0. 870 Ib per 1000 Ib of corrected flue gas.
The three corrected dust loadings vary from
0. 683 to 0. 870 Ib per 1000 Ib of corrected flue
gas, or from well below the above the old
ASME standard, depending on interpretation
of the method of correction. The high moisture
content of incinerator refuse and the effect of ,
sprays cause the difference in results. Stand-
ardization of the method of correcting the dust
loading is needed.
X FLUE-GAS SCRUBBER
The use of flue-gas washers or scrubbers
with incinerators presents interesting thermal
problems which are amenable to calculation.
When this method of gas cleaning is used, the
equipment beyond the combustion chamber is
n duct for quenching of gases, a scrubber with
de-mister, ID fan and stack. The gases leaving
the combustion chamber enter the quench
section where the gases are cooled and satu-
rated with spray water. The gases and excess
water then enter the scrubber proper.
The thermal exchange in the scrubber system
has an important bearing on the composition
of the gas-vapor mixture received by the ID
fan and stack. For the calculations the quench
duct and scrubber may be considered together.
The scrubber water and 1630°F flue gas are
intimately mixed and come to equilibrium at
a temperature which is that of water-saturated
gas, not the boiling point of water. A small
excess of water is supplied to the scrubber
to carry away the trapped fly ash via an over-
flow pipe.
The loss in enthalpy of the flue gas equals
the enthalpy gained by the scrubber water.
Collection efficiency is obtained by an expendi-
ture of fan power. The higher efficiencies are
obtained under conditions of high pressure drop
for initimate contact of gas and water, which
increases the load on the ID fan.
Assume a case in which water is supplied to
the quench duct and scrubber at 80°F. The
water loss to the drain is assumed at 10 gpm
to carry away the solids. The initial enthalpy
(above 80°F) of the flue gas is obtained from
Table 2. Assume a heat loss from the scrub-
ber system to the surroundings of 1. 1 million
Btu/hr in this case.
Determine the quantity of scrubber water re-
quired and the temperature of the scrubber
exhaust. First prepare heat and material
balances to the extent possible. Then solve
by successive approximations of temperature
with use of Reference 5, assuming the dry
flue gas is the same as air. The humidity
ratio of the scrubber exhaust must match that
for air at the exhaust temperature.
The fan capacity is based on the cfm. The
water required by the scrubber equals the
water vapor in the scrubber exhaust plus the
sluice water less the water vapor in the gas
from the combustion chamber: 70, 582 + 4998 -
14,706 = 60,874 Ib/hr or 122 gpm. The ma-
terial balance of the quench section and scrub-
ber is presented in Table 8.
A vapor plume is produced when the scrubber
exhaust enters cold air, which may be unde-
sirable under some conditions and negligible
in others. The amount of water evaporated
in the scrubber- can he reduced by the extrac-
tion of heat from the flue gases ahead of the
scrubber, as by a boiler or heat exchanger.
Reheating the scrubber exhaust is also help-
ful. The vapor plume should be discharged
at a sufficient height to insure that it is
dispersed by natural evaporation without bo-
coming a nuisance or hazard to visibility.
10
-------
Combustion and Heat Calculations for Incinerators
TABLE 1
SCRUBBER HEAT BALANCE. HOURLY BASIS
Table8. SCRUBBER MATERIAL
BALANCE, HOURLY BASIS
Input (1630F from Tobie II)
Dry gos
Water vapor
Carry-over solid*
Unaccounted for heat
Output 175 F
~bry got (42.087- 19.221)(133,375)
Water vapor 70,582(1136.17-48.05)
Heat in drain water.
4998 (175-4B.O)
Heat in trapped iclids,
360(0.251(175-80)
Heot in escape lolidt
40(0.251(175.80)
Heat loss to air from apparatus
Btuh
54,417,000
26,882,568
155,000
135,782
81,590,350
3,049,753
76,401,686
621,546
8,550
950
1,100,000
7 865
81,590,350
Per Cent
66.6
33.0
0.2
0.2
100.0
3.7
94.3
0.7
.
_
1.3
100.0
The volume of gas-vapor mixture at standard barometer,
(30 in. Hg) and 175F is as follows:
CO,: 16,073 (8.548) (460+ I75)/(520)(60) = 2,760
0,: 17.073 (11.819) (635)/(520)(60) - 4,110
N,: 100,229 (13.443) (635)/(520)(60) : 27,400
H,0: 70,582 (I3.47S)/(0.5292) 60 = 29,950
203,957 Ib/hr Total 64,220 cfm
XI GAS AND VAPOR VOLUMES AND
FLOW RATES
The data in the previous tables enable one to
calculate volumes and flow rates for the
purpose of sizing equipment.
A Furnace and Combustion Chamber
Air at 80 F, 60 per cent humidity.
Volume of 1 Ib dry air = 13.601 X
29.92/30.0 = 13.56 cu ft
Volume of water vapor = 0. 60 X 0. 486 X
29.92/30.0 = 0.29
Ambient air volume per Ib dry air at 30 in. Hg
= 13.85 cu ft
130, 422 (13. 85)/60 = 30. 106 cfm air and air
moisture to furnace and combustion chamber.
Density of air to fan inlet = 1.0132/13. 85 =
0.0731 Ib/cu ft
Dry gas
Water vapor
Carry-over solids
Water
Ib/hr
133, 375
14,706
400
60,874
Total, hourly 209, 355
Output
Dry gas 133,375
Water vapor 14, 706 + 55, 876 70, 582
Solids in exit gas at 90 per 40
cent collection efficiency
Scrubber water to drain 4,998
solids to drain 360
Total, hourly 209, 355
The humidity ratio of scrubber exhaust
= 70,582/133, 375 = 0.5292 Ib/lb dry gas.
which is the humidity ratio of saturated
air at 175°F.
B Combustion-Chamber Outlet and Spray-
Chamber Inlet: 148, 081 Ib/hr
Cfm
Water vapor at 1630F: Sp. vol. = 84.64
cu fr/lb 14,706 (84.64)760 20,745
Dry gas volumes
CO,: 16,073 (8.548X460 + 1630)/
(460 + 60) (60) r 9,200
0,: 17.073(11.819)(2090)/(520)(60) - 13,530
N,-. 100,229(13.443)(2090)/(520)(60)= 90,050
Total cfm at 1630F 133.525 cfm
Sp. vol. of furnace gas = 60 (133.525)/
148,081 r 54.1 cu ft/lh
C Spray-Chamber Outlet and Dry Dust-
Separator Inlet
11
-------
Combustion and Heat Calculations for Incinerators
Water vapor at 600F, Sp. vol. = 42.86
cu ft/lb 43,880 (42.86)/60
Dry furnace gas
CO,. 16,073 (8.548)(460 + <>00)/
(460 i 60K60)
0,. 28,498 U1.819)(1060)/(520)(60)=
N,: 138,154 U 3.443X1060)7
(520)(60)
Cfm
31,345
4,670
11,450
= 63,100
Total cfm at 600F 109,565 cfm
Sp. vol. of exit gas = 60 (109,565)7
226,605
D Scrubber Exhaust
= 29.0 cu ft/lb
When the scrubber receives untempered
gas from the combustion chamber, the
scrubber exhausts at 175°F. The exhaust
cfm at 30 in. Hg abs. pressure is 64, 220
cfm and the density is 203, 957/(64, 220)
(60) = 0.0530 Ib per cu ft.
XII SUMMARY
A A hypothetical municipal incinerator oper-
ating at 240 tons a day capacity was used
as an example to present the methods for
calculating the following items:
1 Refuse composition for combustion
calculation.
2 Air required for combustion and tem-
perature control.
3 Gas analyses, excess air, fuel-air
ratios.
4 Heat and material balances.
5 Tempering of combustion gases by
spray water and air.
6 Dry dust collectors and gas scrubbers.
7 Dust loading of stack gases, corrected
to 50 per cent excess air and to 12 per
cent CO2-
8 Flow rates and densities of gas-vapor
mixtures.
B When burning a refuse of 4230 Btu/lb heat-
ing value, 130 per cent excess air is re-
quired for a gas temperature of 1630 F
leaving the combustion chamber.
The flue gas consists of CO2 8. 15 per cent,
O2 11. 96 per cent and N2 79. 89 per cent by
volume, dry basis. The weight of air re-
quired is 6. 5 times the weight of refuse.
C To cool the furnace gases from 1630 to
600°F, requires about 2.50 Ib air and
1. 43 Ib spray water evaporation per Ib
refuse, or equivalent proportions of these
coolants. Sluice water to remove trapped
ash is additional.
D A gas scrubber that received gases directly
from the combustion chamber at 1630 F
would evaporate 2.79 Ib water per Ib refuse.
The scrubber would exhaust at 175°F and
the gases would contain 3.53 Ib water per
Ib refuse.
E Because of high content of water vapor in
incinerator stack gases, several different
corrected dust loadings can be calculated
from the same test data. Calculations for
the example incinerator show that the cor-
rected dust loading per 1000 Ib stack gas
is considerably lower at 50 per cent ex-
cess air than at 12 per cent CO .
ACKNOWLEDGMENT
The research in this paper was supported by
grant EF-00530-01 from U.S. Public Health
Service, Division of Environmental Engineer-
ing and Food Protection.
REFERENCES
1 Steam, Its Generation and Use. The Bab-
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Appendix 37th ed. 1955.
2 Municipal Incinerator Design. Prepared
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3 Damiano, D. J. Incinerator Refractory
Studies. The American City. April
1962.
International Critical Tables.
1926. p. 167.
Vol. 5,
12
-------
Combustion and Heat Calculations for Incinerators
ASHRAE Guide and Data Book. Published 6 Example Sections for a Smoke Regulation
annually by American Society of Heat- Ordinance. Information Bulletin pub-
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J3
-------
BIBLIOGRAPHY ON INCINERATION OF REFUSE
The following bibliography on incineration of refuse was compiled in two parts.
For convenience both parts have been integrated alphabetically according to the
author's last name. The following references were consulted in preparing Part
I of the bibliography:
1 Library of Congress Bibliography on Air Pollution.
2 San Francisco Bay Area Air Pollution Control District,
Uniterm Cards (through June, 1960).
3 Engineering Index, 1945 - 1955.
4 Chemical Abstracts, 1945 - 1956.
5 APCA Abstracts, January 1957 - October 1960.
References consulted for Part II of the bibliography include'the following:
1 Engineering Index (Jan. 1961 -Aug. 1965).
2 Science and Technology Index (Jan. 1961 - July 1965).
3 APCA Abstracts (Jan. 1961- Aug. 1965).
4 Public Health Engineering Abstracts (Jan. 1962 - July 1965).
5 Chemical Abstracts (1961 - July 1965).
6 Library of Congress - Air Pollution Index.
7 "Disposal - Incineration". Section of Unpublished Annotated Bibliography.
Supplement F, Refuse Collection and Disposal 1962 - 1963, U. S. Public
Health Service.
8 Bay Area Air Pollution Control District Uniterm File (1961 - 1964).
""Compiled by Air Pollution Training Section, Training Program, U.S. Public
Health Service, Division of Air Pollution. Part I was prepared in 1961 by the
Engineering Research and Development Section, Laboratory of Engineering and
Physical Sciences (Cincinnati). Part II was prepared in 1965 by the Engineering
Control Section, Technical Assistance Branch (Cincinnati).
PA.C. ce.2. 1.66
-------
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Auto Burning Problems Eased. APCA
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Bibliography on Incineration of Refuse
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18
-------
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-------
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21
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23
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Section 4
BURNING OF GAS AEROSOL WASTE
Catalytic, Furnace and Flare Combustion - Basic
Concepts and Selected Applications
Catalytic Incineration
Catalytic Incineration - Design Parameters and
Operation Practices (by Clark)
Catalytic Incineration - Design Parameters and
Operation Practices (by Romeo, et al.)
Thermo Oxidation
Thermo Oxidation of Gaseous and Aerosol Waste
Controlled Endo-Exothermic Oxidation of
Industrial Wastes
Flare Combusticm
Flare Combustion
Flare Burning of Waste Gases
-------
CATALYTIC, FURNACE AND FLARE COMBUSTION-
BASIC CONCEPTS AND SELECTED APPLICATIONS
Darryl J. von Lehmden-
I INTRODUCTION
Many organic compounds released from manu-
facturing operations can be converted to
innocuous carbon dioxide and water by rapid
oxidation -- combustion. Three rapid oxi-
dation methods are used to destroy combus-
tible contaminates: 1) furnaces, 2) flares
and 3) catalytic combustion. The furnace
and flare methods are characterized by the
presence of a flame during combustion.
Whereas, catalytic combustion utilizes a
metallic catalyst to promote rapid oxidation.
Catalytic combustion is a flameless-type
combustion.
II BASIC CONCEPTS
A Flare Combustion
All process plants which handle hydro-
carbons, hydrogen, ammonia, hydrogen
cyanide, or other toxic or dangerous gases
are subject to emergency conditions which
occasionally require immediate release
of large volumes of such gases for pro-
tection of plant and personnel. In many
petrochemical processes, hydrocarbons
present with inert gases, such as nitrogen
and carbon dioxide, must be continuously
released in variable volume and concen-
tration. Where these gases are released
at energy concentrations constantly within
or above the flammable range, their
disposal can be handled most economically
and safely by application of flares. How-
ever, smokeless burning of hugh quantities
of gases by flares presents some serious
design problems. First, the flare must
be sufficiently elevated above ground level
for heat and flame protection of adjacent
buildings and personnel. Flame must be
sustained at varying rates, exceeding by
many times to operating range of indus-
trial burners. These physical demands
prevent the employment of combustion
chambers.
*Chemical Engineer, Air Pollution Training,
Training Program, SEC
Flare combustion is often characterized
by a luminous (yellow) flame. The lumi-
nous flame results when oxygen in the air
surrounding the flame comes in contact
with the hydrocarbons by diffusion only.
The luminous color results from incan-
descent carbon which result from the
cracking of the hydrocarbon molecules.
Blue-flame flare combustion can be ac-
complished by adding water vapor, under
proper temperature conditions, as the
gas is burned. A water-gas reaction is
set up, generating carbon monoxide and
hydrogen which assists in the production
of blue flame burning by removing the
unburned carbon. Combustion of carbon
monoxide and hydrogen results in carbon
dioxide and water.
C + HO = CO +
co + io = co
(water-gas
reaction)
H + iO = HO
£ 6 £
One design of a steam injected flare is
illustrated in Figure 1. * ^
B Furnace Combustion
Whereas flares are effective in destroying
waste gases which are released continuous-
ly or periodically at concentrations above
the lower limit of flammability, gases
vented from industrial processes are
generally exhausted at concentrations far
below the lower flammable limit. At
these concentrations of gases, combustion
in an enclosed chamber is necessary.
Furnace combustion is commonly called
"direct flame incineration" since a
separately fired burner is normally em-
ployed to sustain rapid oxidation. The
flame, per se, has no influence on the
PA.C.ce. 7. 1. 66 1
-------
Catalytic. Furnace and Flare Combustion - Basic Concepts and Selected Application
reaction except as it provides the time -
temperature - turbulence factors.
Since "the three T's" allow considerable
latitude in design, numerous combinations
of the "three T's" will result in complete
combustion. Generally, however, furnace
construction costs requires a practical
limit on holding time.
When there is 1 percent or less (by volume)
combustible matter in a gas stream of
otherwise inert material, experience
shows*3' clearly that design temperature
in the order of 1800°F to 2000°F with a
residence time of 3 to 5 seconds in the
presence of not less than 25% excess air
will be required to secure complete oxida-
tion of some combustibles, particularly
odors with low threshold limits.
FLARE TIP
PILOT TIP
A diagram of a waste gas and odor-
incinerator is shown in Figure 2.
;|TU« f*
ITltL H»TI
imuutiM piMMiet
.... mi
lUPMRtl
IM IUIIIH
IAI MV
•ill liTilUM
STEAM
JETS
LAME FRONT
IGNITOft TIP
"L»MC FRONT
CNITOH TUBE
STEAM
SUPPLY LINE
PILOT MIXER
PILOT CAS CONN.
J-WAY
PLUG VALVE 3
O PILOT-I
(ICTIM I
MCTIM *
Figure 1. STEAM INJECTION TYPE FLARE
Figure 2. DIAGRAM OF A WASTE GAS
AND ODOR INCINERATOR
C Catalytic Combustion
Catalytic combustion is the lowest
temperature method of rapidly oxidizing
combustible gases and vapors. Many
substances exhibit catalytic properties,
but metals in the platinum family are
recognized for their ability to produce
the lowest catalytic ignition temperatures
and are therefore conventionally used.
Since catalytic oxidation is a surface
reaction, relatively small amount of
platinum are used in a way which exposes
the maximum surface area to the gas
stream. This is accomplished by coating
a high surface area substance with the
catalyst and arranging the catalyst coated
substances in catalyst beds.
Sufficient surface area must be supplied
to permit the oxidation reaction to be com-
pleted within the bed, since "the three T's"
still apply if "exposed catalyst surface"
is substituted for "time. " Turbulence is
achieved in the passage of the contaminated
gases through the bed. Catalyst tempera-
ture results from the oxidation reaction
itself, plus burner or electric preheating
where necessary. With platinum alloy
catalysts, oxidation of hydrogen will be
initiated at ambient temperature, naptha
at 450°F, and methane at 750°F. ^'
-------
Catalytic, Furnace and Flare Combustion - Basic Concepts and Selected Applications
The temperatures required to catalytically
oxidize many organic compounds are given
in Table 1.
Catalytic combustion is generally appli-
cable where the following conditions apply:
1) where the gas stream to be handled
contains vaporized or gaseous combustible
materials, and 2) where there is no large
amount of dust, fly ash, or other solid
inorganic material in the gas stream.
Catalytic systems are designed to prevent
condensate formation in exhaust equipment.
The exhaust fan in a catalytic system is
located on the hot side of the system so
that all vapors passing through it are above
the condensation temperature.
A typical catalytic combustion systejn
employing a preheat burner is shown in
Figure 3. (1>
Heat evolved by the catalytic oxidation can
also be used to preheat the gas stream.
Figure 4< ' shows a heat exchanger and
preheat burner arrangement to heat the
gas stream to the catalytic ignition
temperature.
Ill SELECTED APPLICATION OF COMBUS-
TION TO AIR POLLUTION CONTROL
A Flare Combustion
Table 1. INDUSTRIAL APPLICATIONS OF CATALYTIC COMBUSTION
Industrial process
Contaminating agents
In waste gases
Approximate temperature
required for
catalytic oxidation
Asphalt Oxidizing
Carbon Black Mfg.
Catalytic Cracking
Units
Core Ovens
Formaldehyde Mfg.
HNO3 Mfg.
Metal Lithography
Ovens
Octyl-phenol Mfg.
Phthalic Anhydride
Mfg.
Polyethylene Mfg.
Printing Presses
Varnish Cooking
Wire Coating and
Enameling Ovens
Aldehydes, Anthracenes,
Oil Vapors, Hydrocarbons
H2, CO, CH4, Carbon
CO, Hydrocarbons
Wax, Oil Vapors
H2, CH4, CO, HCHO
NO, NO2
Solvents, Resins
Maleic Acid, Phthalic Acid,
Naphthaquinones, Carbon
Monoxide, Formaldehyde
Hydrocarbons
Solvents
Hydrocarbon Vapors
Solvents, Varnish
600°
*1200°
650°
600°
** 500°
500^
600°
700°F
1800°F
800°F
700°F
650°F
1200°F
750°F
800°F
600° - 650°F
500 - 1200°F
600°F
600° - 700°F
600° - 700°F
* Temperatures in excess of 1200°F required to oxidize carbon,
** Reducing atmosphere required.
-------
Catalytic, Furnace and Flare Combustion - Basic Concepts and Selected Applications
E.howt
ton
HEAT EXCHANGER>
EXHAUS
J ,
"1
/•PREHEAT BURNER
OXYCATSx
M
V V • Z=
p
FROM PROCESS
Figure 3. CATALYTIC COMBUSTION SYSTEM
INCLUDING PREHEAT BURNER AND
EXHAUST FAN
Dimethylamine odor control during
the manufacture of soaps and
detergents'5
New and improved products for the
consumer requires new processes
and new chemical raw materials. The
manufacture of new products by a soap
and detergent company required the
use of dimethylamine as a raw material.
Dimethylamine (jSTH (CH3)^) is a
gaseous material at 40°F and atmos-
pheric pressure. The material is a
first cousin of ammonia (NHg) and at
concentrations in excess of 100 ppm
the odor of this a mine is nearly
identical to that of ammonia. As the
amine concentration becomes diluted
it takes on an odor resembling fish
which has been in the sun too long. As
the concentration falls below 100 ppm
the fish odor becomes predominant over
the ammonia odor.
Figure 4. CATALYTIC COMBUSTION
SYSTEM INCLUDING HEAT EXCHANGER,
PREHEAT BURNER AND HEAT FAN
In order to protect residence 2500 feet
from the plant from this fishy odor a
method was needed to destroy the di-
methylamine emissions. The solution
to this odor problem was obtained
through the use of a 100-foot flare
stack. The amine-laden waste gases
are vented to a holding tank for storage.
A continuous flow of the amine-laden
gases enters the base of the flare stack;
passes through a flame arrestor and
are incinerated at the top of the flare
stack. The stack is equipped with four
natural gas pilot lights to assure igni-
tion of all combustibles released from
the stack. The result has been a smoke-
less flare which reduces the odor pro-
blem several orders of magnitude.
B Furnace Combustion
1 Methyl mercaptan, hydrogen sulfide
and methyl sulfides odor control from
the Kraft Pulping Process^6'
Odors resulting from the Kraft (sulfate)
pulping process have been reduced by
rapid oxidation of the non-condensable
gases emitted from the black liquor.
-------
Catalytic, Furnace and Flare Combustion - Basic Concepts and Selected Applications
Gaseous emissions from the black liquor
contain the odorous compounds, methyl
mercaptan, hydrogen sulfide and
methyl sulfide. The oxidation of these
compounds results in sulfur compounds
which are less volatile and therefore
less odorous than the original
contaminants.
Several west coasts pulp and paper
mills have installed equipment to
incinerate these odorous sulfur gases.
One mill utilizes an integral part of
the Kraft process, the lime kiln, to
incinerate the odors. Another method
of reducing the odors has been the
oxidation of the black liquor itself.
Emissions of gaseous sulfur compounds
may be as high as 100 pounds per ton of
pulp from an uncontrolled Kraft process.
Vapor control from paint and varnish
cookers* '
In the burning of combustible vapors
from paint and varnish cookers,
adequate consideration must be given
to prevent fire or explosion in the
kettle as a result of flashback through
the vapor. Safeguards can be achieved
by diluting the vapor concentration to
less than 25 percent of the lower ex-
plosive limit and by maintaining gas
velocities in the ducts well in excess of
20 feet per second, the rate at which
flame could propagate along the duct.
A fume (vapor) combustion system for
incinerating vapors from paint and
varnish cookers is shown in Figure 5.
A correctly proportioned and well in-
sulated furnace requires a fuel input
between 600 and 1200 BTU per hour
per gallon of processed batch. In
some processes, enough vapors are
produced to appreciably supplement
the regular fuel.
Discharge to
stack
Closed Kettle
Open Kettles
Figure 5. LAYOUT OF FUME COMBUSTION SYSTEM FOR PAINT AND VARNISH COOKING
-------
Catalytic, Furnace and Flare Combustion - Basic Concepts and Selected Applications
3 Odor control from coffee roasters^8)
The combustibles in coffee roasting
effluent gases may be present in con-
centration ranging from 0. 17 to 0. 27
grains per cubic feet, depending upon
the type of roaster and the rate of
exhaust flow.
The roaster exhaust gases include the
following compounds: formic acid,
high fatty acids, furfural, methylamine,
pyrole, acetic acid, acetone, ammonia
pyridine and hydroquinone.
Furnace combustion is presently being
employed to incinerate the combustible
gases from coffee roasters and to re-
duce the odor per se.
C Catalytic Combustion
1 Catalytic oxidation of lithographic oven
Catalytic combustion is used in many
industrial processes to destroy odors
and contaminant gases. Among the
processes in which catalytic oxidation
is used includes varnish cooking, carbon
black manufacture and metal lithographic
ovens.
Figure 6 shows a catalytic oxidation
system used on a metal lithographic
oven. Here a portion of the process
effluent, after having been catalyzed
and cleaned, is channeled back to a
lithographying oven. The returned
exhaust, split among several zones
in the oven, provides all or a part of
the oven heat requirements. Excess
exhaust over that needed to heat the
oven is vented directly to the atmosphere.
Catalytic reduction (deoxidation) of
nitrogen oxides in waste gases from
nitric acid manufacture'
Catalytic combustion is also used to
reduce contaminants to lower oxidation-
state compounds. Waste gases (tailgas)
from the manufacture of nitric acid
contain NO, NO2 and nitric acid vapors.
Concentrations of nitrogen oxides in
these waste gases range from less than
0. 1 percent to almost 50 percent by
volume. By mixing a hydrocarbon
(e. g. , methane) or reactive fuel (e. g.,
carbon monoxide with the waste gases
and passing the gases through a catalyst,
the following reaction takes place if
the reaction goes to completion.
+ (n) HC = (n) HO + (n CO + (n N
Litho - Oven
Catelyit B«d S Fr«»h Air Domoef
Automatically
Controlled
Figure 6. CATALYTIC OXIDATION OF SOLVENT FROM METAL LITHOGRAPHIC OVENS
-------
Catalytic, Furnace and Flare Combustion - Basic Concepts and Selected Applications
EXHAUST
FAN
This reaction can be made to proceed
at comparatively low temperature
(500 - 1200°F}* The amount of free
oxygen contained in the waste gas
stream presumably influences the ease
with which the reaction can be completed.
Obviously, when the waste gas stream i«
is entirely devoid of free oxygen, then
oxidation of the hydrocarbons can occur
only through simultaneous reduction of
the nitrogen oxides to a lower oxidation
state or free nitrogen.
A schematic of a catalytic reduction
system for nitric acid waste gases is
shown in Figure 7.
EXHAUST
TO ATMOSPHERE
CATALYST
BED
RECYCLING
GASES
PREHEAT
BURNER
REDUCING
FUEL
PROCESS
WASTE GASES
Figure 7. SCHEMATIC OF CATALYTICAL
REDUCTION SYSTEM FOR NO,,
2 Coward, H. F. et al. U. S. Bureau of
Mines - Bulletin 503. Vol. 4, 1952.
3 Reed, R. D. Controlled Endo-Exothermic
Oxidation of Industrial Waste. Pre-
sented at Waste Disposal Conference,
Oklahoma State University. Nov. 16,
1965.
4 Oxy-Catalyst, Inc. Basic Engineering
Principles of the Oxycat. Berwyn,
Pennsylvania.
5 Byrd, J. F. et al. Solving a Major Odor
Problem in a Chemical Process.
JAPCA, Vol. 14, pp 509-516.
December, 1964.
6 Hendrickson, E. R. et al. Black Liquor
Oxidation as a Method for Reducing
Air Pollution from Sulfate Pulping.
JAPCA, Vol. 14, pp 487-490.
December, 1964.
7 Stenburg, R. L. Control of Atmospheric
Emissions From Paint and Varnish
Manufacturing Operation. U. S. Public
Health Service. R. A. Taft Sanitary
Engineering Center. Technical Report
A58-4.
8 Anon. Discussion of Coffee Roasting
Process. LAAPCD.
REFERENCES
1 Stern, A. C. Air Pollution. Academic
Press, New York City, Vol. II.
Chapter 32.
9 MacKnight, R. J. et al. Controlling the
Flue-Fed Incinerator. JAPCA, Vol.
10. April, 1960.
10 Donahue, J. L. System Designs for the
Catalytic Decomposition of Nitrogen
Oxides. JAPCA, Vol. 8, pp 209-212,
222. November, 1958.
*Table 1.
-------
CATALYTIC INCINERATION-DESIGN PARAMETERS
AND OPERATION PRACTICES
L. W. Clark*
In order to become familiar with the rudi-
mentals of catalytic incineration design I feel
the best procedure would be to follow through
a simple design example. Accordingly, the
following would be representative of a typical
catalytic incineration problem.
One gal/hr of napthalene is being emitted
from an oven operation in a gas volume
of 100,000 SCFH at 200°F. It is desired
to remove at least 907o of the napthalene
and, if possible, provide heat exchange
to heat the oven intake air to 200°F.
Natural gas and 440 volt electricity are
available as utilities.
The first step is to determine the catalyst
entry temperature of the heated gas from
the burner. The temperature to which the
gas is heated is a function of the ease of
oxidation of the contaminators along with the
desired efficiency. Alcohols, ketones and
aromatics are relatively easy and require
an entry temperature of roughly 600°F,
whereas tars and asphaltic vapors need a
900°F temperature. A difficult odor re-
moval problem may also require the higher
oxidation temperatures. For our problem
we will choose a 600°F entry temperature.
Next we will determine the heat duty of the
burner by first determining the heat required
to raise 100,000 SCFH of 200°F gas to 600°F
by the following calculation:
100, 000 SCFH X
X (600-200)°F =
BTU
755,000
hr.
Q = Q inlet gas +
(quantity of combustion gas)
However, for burner sizing an integration
factor of I/. 7 is commonly used giving an
operating heat duty of:
Q = I/. 7 X 755,000 = 1.08X 106 BTU/hr.
Our problem calls for 1. 08 X 10G BTU/hr. ;
and natural gas has a heat capacity of 1000
BTU/SCF. This means 1080 SCFH of gas
which combined with a 10 to 1 ratio of com-
bustion air gives 11, 880 SCFH of combustion
products to be heated under operating con-
ditions. Consequently, the effect of com-
bustion air is significant.
The maximum heat duty of the burner occurs
during start-up when cold air is heated to
the catalyst entry temperature before the
contaminated gases are introduced,
Q « 100,000 X 1/53 X (600 - 70) X 1 /. 7 X 1. 25
This heat duty might be considered a pre-
liminary estimate. There is a fallacy in the
calculation for we neglected to include the
heating of the combustion air. Theoretically
this is a calculus integration over the tem-
perature range.
*Sales Engineer, Chemical and Process Industries,
Air Correction Division, Universal Oil Products.
PA.C.ce.37. 1.67
hr.
The burner itself may be of the atmospheric
type when the system is under suction. This
type of burner has an effective turn-down
ratio of 3 to 1 which fits our requirements.
The natural gas should be available with at
least 4-6 inches water gage pressure.
The fan for moving the contaminated gas is
preferably installed between the burner and
the catalyst. This allows for an atmospheric
burner and for complete mixing of the gases
before reaching the catalyst. Pressure
-------
Catalytic Incineration
burners are not uncommon in catalytic work,
but they need combustion air at 4 - 6 inches
water gage pressure requiring a blower.
However, the pressure burner does have a
10:1 turn-down ratio, and it is necessary for
fuel oil burning.
Most catalysts for air pollution work are a
platinum, palladium alloy with only occasional
traces of rhodium and ruthenium. Generally,
palladium seems to be the most effective and
is used in heavier concentrations for the
difficult oxidations of methane and nitrogen
oxides.
The choice of catalyst support is a more
arbitrary decision than the type of catalyst
and perhaps the best procedure would be to
list the various types and their characteristics.
1 Alumina or ceramic honeycomb
advantages:
a effective use of surface area in pitted
nature of substance and in design;
b low pressure drop - a 12 inch depth
has roughly a 0. 5 inches water gage
drop.
disadvantages:
a cannot be reactivated or washed;
b breakable due to brittleness.
2 Wire ribbon - a chromium-nickel alloy
best suited for corrosion, heat resistance
and ease of electrolytic coating.
advantages:
a low pressure drop;
b ability to reactivate and wash;
c very rugged with the ribbon inclined
to hold in the absence of a retaining
screen.
disadvantages:
a perhaps not as effective use of
surface area;
b heat destruction of the metal at
continuous 1400°F temperatures.
However, the catalyst also vaporizes
at this temperature.
3 Ceramic spheres
advantages:
a reasonable use of surface area.
disadvantages:
a high pressure drop - roughly three
times that of the honeycomb and
ribbon;
b must be effectively retained by a
screen.
4 Wire screen - Sufficient for easy oxi-
dations where surface contact can be
inefficient. Very low pressure drop
is involved, but screens are not good
for any degree of difficulty in oxidation.
Returning to our example, the next step is to
determine the number of catalyst elements.
Our ribbon design is available in an 18 X 24
inch unit. The D-2 unit is 2 1/2 inches thick
and designed for 600 SCFM. For our 100,000
SCFM three elements are required. It is
possible to have a thicker unit, but the system
pays for it in pressure drop. For instance
a D-3 element has 1. 2 inches water gage
pressure drop for 33/4 inches thickness but
is capable of 960 SCFM or two elements for
our example. The reason for this considera-
tion is the smaller housing.
The enthalpy of napthalene is 120,000 BTU/gal.
Our loading then produces a 120,000 BTU/hr.
heat content of organics. The outlet tempera-
ture of the gas leaving the catalyst can then
be calculated:
120,000
BTU
X
hr. 100,000 SCFH
X 53 = 63. 5°F
From the catalyst we now have 100,000 SCFH
of air at 663°F. This air is to be passed
through a heat exchanger, but preferably not
to cool beneath 400°F due to condensation
considerations in downstream equipment.
Typically, a tubular heat exchanger of 2 1/2
inch tubes would be considered. An overall
-------
Catalytic Incineration
heat transfer coefficient is roughly 3. 5
BTU/hr. -ft2- °F. Assuming the same
100,000 SCFH of air is to be heated from
70°F to 200°F, the following determines the
surface area of the heat exchanger:
Q - U A delta
whe re :
Q = 100,000 SCFH X (663 -400)°F X
1/53 BTU/SCF - °F
Q = 4.96X 105 BTU/hr.
delta T = (40° - 70> - <663 - 20°) - 388oF
delta TLM Ln 330/463 388 F
4. 96X1Q5
388X3.5
ft
There are two standard instruments provided
with the catalytic incinerator. A burner con-
troller is placed before the catalyst to insure
a constant temperature to the catalyst. A
high-low limit is placed before and after the
catalyst, and by flipping a switch the tempera-
ture rise across the catalyst can be read.
The lower limit is set for roughly 550°F and is
used primarily for start-up. The system will
heat-up on air until 550°F when a damper
isolating the process opens. This prevents
unburned organics from passing through the
system eliminating the possibility of deposits
on the catalyst. The high limit set for 1200°F
cuts out the burner and closes the damper to
the process in order to protect the materials
of construction.
Usually a heat resistant steel is suitable for
the housing of the unit. Our product uses
Armco steel - steel with an aluminum alloy
plating - as an inner liner with a 4 inch thick
rock wool insulation and a 20 gage steel
jacket. This type of steel can be used due to
the lower operating temperatures relative to
a thermal system. Occasionally stainless
steel is used for heat and corrosion resistance.
No differentiation is made between the pre-
heat and combustion zone.
The life of the catalyst is normally three to
five years depending on the service and up-
keep. The catalyst life is not so much a
function of the gases being oxidized as the
presence of the various contaminents, such
as the following:
1
A dirty environment causing the
catalyst to be coated.
Catalyst poisons which may be as
simple as galvanized ductwork. Typical
poisons are Pb, Zn, Hg, Cu, Fe, Sb,
Bi, phosphates and silicones.
Suppressants which slowly destroy the
catalyst activity. Common suppres-
sants are the halogens of F, Cl, Br,
and I and the sulfur compounds of
H2S, SC>2 and the sulfates. A suppres-
sant may be periodically washed off
the catalyst by a mild acid solution,
but there is an unpredictable degree of
reactivation.
High temperature excursions vaporizing
the catalysts.
Low temperature start-up causing
organic particulates to reach the
catalysts, which in turn cause carboni-
zation on the catalyst.
-------
CATALYTIC INCINERATION-DESIGN PARAMETERS
AND OPERATION PRACTICES
P.L. Romeo and A. Warsh*
The removal of objectionable gases and
vapors from industrial process off-gases is
usually accomplished by one of the following
methods.
1 Absorption in a liquid
2 Adsorption on a solid
3 Chemical conversion to an innocuous
compound
a non-catalytic
b catalytic
4 Incineration
a non-catalytic
b catalytic
An economic or technical evaluation describ-
ing the comparative advantages and disad-
vantages of each method is beyond the scope
of this discussion.
Briefly, however, it is safe to say that
under ideal conditions and where the objec-
tionable component has a substantial salvage
or re-use value, methods (1) and (2) are
generally preferred. Where the value of the
objectionable component is low, and purity
of the recovered product is beyond tolerable
limits, methods (1) and (2) are difficult to
justify.
Therefore, one is left to choose between
chemical conversion or incineration. From
a chemical and economical standpoint, the
choice between chemical conversion and in-
cineration is often relatively clear cut.
However, should incineration be indicated,
the choice between catalytic and non-catalytic
treatment is not easily determined and many
factors must be considered.
Examples of chemical conversion are the
non-catalytic oxidation of various hydro-
carbons to carbon dioxide in permanant
solutions; and the catalytic reduction of
nitrogen dioxide to nitrogen and water using
ammonia as the reducing agent.
At this point in the discussion, it may be
worthwhile to define the basic differences
between catalytic and non-catalytic
incineration.
In order for non-catalytic incineration to be
considered, the concentration of both
oxygen and the combustible impurity must
be within the limits of flammability, which
is defined as the maximum and minimum
percentages of a fuel in an air-fuel mixture
which will burn. Concentrations of combust-
ibles outside these limits are not flammable
by the usual interpretation.
The energy contained in a mixture of air and
fuel, while at the lower flammable limit,
is - almost without regard to the type of
fuel - equivalent to approximately 52 BTU
per SCF. At room temperature, therefore,
the combustible in the air must provide at
least 52 BTU per SCF in order that a flame
may be initiated by a high temperature source,
and be self sustaining. If these conditions
are not satisfied, the gas temperature must
be raised above the auto-ignition point of
the component to be removed in order to
permit the oxidation reaction to occur; or
auxiliary fuel and/or oxygen (air) must be
added to provide for burning on a self pro-
pagating basis.
Because of safety considerations, high con-
centrations of undesirable combustibles are
generally diluted to 25% or less of the lower
explosive (flammability) limit and heat is
provided by independently burning a second
source of fuel.
*Engelhard Industries, Inc., Gas Equipment Division,
East Newark, New Jersey
PA.C.ce. 35. 5. 66
-------
Catalytic Incineration Parameters and Operating Practices
Catalytic incineration, on the other hand,
can be accomplished in any concentration
range and is usually limited only by the
prescribed operating temperature limits
of the catalyst and related equipment. A
point worth mentioning is the catalytic in-
cineration is flameless.
In general, where large amounts of the
undesired combustible impurities are pre -
sent, and sufficient heat and oxygen is
already available, non-catalytic treatment
is often more economical. However, in the
case of streams with widely varying amounts
of impurities or where preheat is required,
catalytic treatment offers many advantages.
Table 1 compares auto-ignition temperatures
for various substances with experimentally
determined catalytic ignition temperatures.
From the table, it can be seen that signifi-
cantly less heat must be required to raise
the gas temperature to that required for
combustion via the catalytic method as
opposed to the non-catalytic method.
It has been found that for a simple catalytic
incinerator, with the same capital invest-
ment as that required for direct flame in-
cineration, operating fuel costs can, at
times, be as low as 30% of the flame
incinerator. As an example, let us consider
the case of carbon monoxide. Assuming
the carbon monoxide concentration is out-
side the limits of flammability and the
stream is available at ambient temperature,
almost four times as much auxiliary fuel
would be required for flame incineration as
that required for catalytic incirieration.
Having ascertained the applicability of
catalytic incineration, it must then be de-
cided which catalyst will best meet the
needs for the particular application under
consideration.
Contrary to the often expressed axion that
precious metals have a definite order of
reactivity for all reactions, it has been
established that each combustible must be
evaluated individually to ascertain which
metal catalyst exhibits maximum activity
at the lowest ignition temperature.
TABLE 1
Compound Flammability Range Mol% Auto Ignition °F
Acetylene 2.5 - 80 365
Benzene 1. 4 - 7. 1 1076
n-Butane 1. 6 - 8. 5 806
Carbon Monoxide
Hydrogen
Methane
Naphtha
Propane
Xylene
12.5 - 74.2
4. 1 - 74.2
5. 3 - 13.9
1. 1 - 6.
2.4 - 9.5
1.0 - 6.0
1204
1076
999
950
870
924
Catalytic Ign. °F
280
500
570
300
32
800
570
660
570
-------
Catalytic Incineration Parameters and Operating Practice'
The probable cause of this phenomenon can
best be understood if we examine the five
steps in any solid-catalyzed vapor phase
reaction.
The five basic steps in catalysis are:
1 Diffusion of the reactants through
the stagnant fluid around the surface
of the pellet, and diffusion through the
pores of the pellet to the catalytic
surface.
2 Adsorption of reactants on the catalytic
surface.
3 Reaction of the adsorbed reactants to
form products.
4 Desorption of the products from the
catalytic surface.
5 Diffusion of the products through the
pores and surface film to the bulk
vapor phase outside the pellets.
Given the identical support, (e. g., A^C^
pellets), the rate of steps (1) and (5) would
be approximately equal, regardless of the
catalytically dispersed metal which is pre-
sent, for each specific hydrocarbon.
The criteria which govern the order of
reactivity for various catalytic metals must,
therefore, fall into steps (2), (3) or (4).
For example, it is a well-known fact that the
diffusion and adsorption of hydrogen into
palladium is rapid and substantial. (Com-
mercial units utilize this principle for the
generation and purification of hydrogen; e. g. ,
the Palladium-Alloy Diffusion Purifiers).
No other metal approaches palladium in this
property.
One would assume, therefore, that step (2)
would be considerably more rapid when using
a palladium catalyst in the presence of H2,
than for other metals.
This is proven by examining the following
reactions:
H
1/2 O — HO
2) C2H2 +H2 - C2H4
Palladium is, by far, the preferred catalyst
for these reactions under a wide variety of
commercially attainable conditions.
Further examples showing order of reactivity
of hydrocarbon combustions over different
catalysts is given in U.S. Patents 3,056,646
and 3,098, 712.
Not only is the order of reactivity governed
by the hydrocarbon being reacted, but it is
also governed by such factors as the avail-
able excess oxygen, and the availability of
more than the required inlet temperature.
Table 2 is a summary of results obtained,
using methane as a fuel.
Order of Reactivity
1
2
3
4
5
TABLE 2
Neutral Atmosphere
Rhodium
Palladium
Iridium
Ruthenium
Platinum
Oxidizing Atmosphere
Palladium
Rhodium
Ruthenium
Iridium
Platinum
-------
Catalytic Incineration Parameters and Operating Practices
(Economic, as well as technical factors, will
affect the choice of catalyst in individual
cases, and thus palladium may often be
chosen to operate in a neutral atmosphere,
where rhodium shows a slight technical
advantage.) Conclusion:
Each gas purification problem requires
specific evaluation concerning the proper
choice of catalyst for maximum performance.
Operating experience has shown that, while
one metal may prove superior for the oxida-
tion of one compound or class compounds,
the exact reverse may be true for a separate
compound.
WHAT SHAPE CATALYST?
The geometric configuration or individual
catalysts often profoundly influences the
extent and direction of a reaction.
Catalysts are currently supplied in the
following forms:
1 Pellets
2 Spheres
3 Wire Gauze
4 Raschig Rings
5 Low Pressure Drop, Unitary Ceramic
6 Berl Saddles
7 Extrudate
8 Metallic Ribbon
The variety of shapes, coupled with the
variety of catalytic metals, offers a multitude
of catalysts available for each application.
Asa result, a good general rule to follow is
to consult with a catalyst manufacturer on
the most suitable catalyst and optimum bed
configuration.
Catalyst life, in general, is in excess of two
years. In some instances, catalyst charges
have operated satisfactorily for over seven
(7) years without requiring regeneration or
replacement.
Catalysts are susceptible to various poisons.
Among these are base metals, halogens, and
concentrated acids. Poisons of this type have
a cumulative effect and when present in high
concentrations, can shorten catalyst life
appreciably. Recent data also indicates that
the presence of sulfur dioxide has a marked
deleterious effect on catalyst life.
Some types, e. g., pelleted, spherical, and
wire ribbon catalysts, can also act as filters
and become plugged and inoperative when
processing dust-laden gas streams. There-
fore, in these instances, pre-filtration
equipment may also be required.
Table 3 gives an indication of the wide
variety of applications for which catalytic
incineration can be and is used. Table 4
lists the sources of hydrocarbon air pollutants
from a typical refinery operation alone.
Catalytic incineration is flexible in that a
relatively wide variety of systems and puri-
fication schemes can be employed. Figures
1 through 5 schematically depict some
typical systems.
Figure 1 depicts the simplest type of cata-
lytic incineration system. In this case, the
contaminated stream is delivered to the
catalyst element at some constant predeter-
mined temperature, purified over the
catalyst, and vented through a stack. In
such cases, sufficient pressure is already
available in the primary system to overcome
the inherent pressure drop through the
catalytic unit.
In Figure 1 through Figure 5 it is assumed
that sufficient oxygen is already present in
the contaminated stream so that an auxiliary
source of combustion air is not required.
-------
Catalytic Incineration Parameters and Operating Practices
TABLE 3
TYPICAL INDUSTRIAL USES OF CATALYTIC SYSTEMS
Asphalt Blowing
Burnoff Ovens
Chemical Processing
Deep Fat Frying
Fat Rendering
Fish and Vegetable Oil
Processing
Fool Processing
Foundry Core Baking
High Purity Gas Purification
Metal Decorating
Nitric Acid Manufacturing
Paint Baking
Paint and Varnish Kettle Cooking
Paper Printing and Impregnating
Pharmaceutical Manufacturing
Phthalic and Maleic Anhydride
Sewage Disposal
Textile Finishing
Wire Enamelling
TABLE 4
TYPICAL REFINERY SOURCES OF HYDROCARBON
AIR POLLUTANTS WHICH CAN BE TREATED BY CATALYTIC
INCINERATION
Air Blowing
Barometric Condensers
Blind Changing
Blow Down Systems
Boilers
Catalyst Regenerators
Compressor Engines
Cooling Towers
High Pressure Equipment
Handling
Decoking
Loading Facilities
Process Heating
Pumps
Storage Tanks
Sampling
Turnarounds
Vacuum Jets
Valves
Waste Water Separators
Incinerators
It should be pointed out, however, that in
many cases either sufficient oxygen for
complete combustion is not available, or the
gas velocity is not adequate to provide for
good premixing. In these instances, make
up combustion air must be supplied, which in
many cases necessitates the addition of a
secondary air mover to the system.
Figure 2 depicts a system into which a
secondary air mover has been incorporated
because the primary system pressure was
insufficient to overcome the pressure drop
across the incinerator.
Please note that the preheat burner is
located ahead of (up stream) the blower.
-------
Catalytic Incineration Parameters and Operating Practices
Although locating the blower at this point
requires more expensive materials of con-
struction, two important operating advantages
are gained, namely;
1) Condensation of vapors on the fan
blades is minimized thus requiring
less frequent maintenance.
2) Adequate mixing of hot and cold gases
is obtained in the blower prior to
entry into the catalyst bed, thereby
insuring uniform reaction.
Figure 3 depicts a somewhat more elaborate
system which incorporates two additional
features.
A recycle damper (F) has been added to pro-
vide for the mixing of the hot purified effluent
gas with the cold inlet gas, thereby minimiz-
ing fuel requirements. Naturally, only a
portion of the hot purified gas is mixed with
the inlet gas. This feature is often used
where the concentration of the undesirable
or combustible impurity in the inlet stream
exceeds 25% of the lower explosive limit.
The addition of the effluent gas dilutes the
combustible concentration to a tolerable
level.
"CLEAN
STREAM
A second feature incorporated into the
system is the counter-current heat exchanger
(G). A portion of the heat produced during
the catalytic incineration of the undesirable
combustible is transferred to the cold inlet
gas stream thereby further minimizing fuel
requirements.
These features may be used separately or
together depending on individual process
requirements.
Figure 4 depicts the ideal situation where
sufficient combustibles are liberated from
the primary process (A) to supply, after
catalytic incineration in the pollution abate-
ment equipment (E) a substantial portion of
the energy requirements for the process.
Examples of applications where the decon-
taminated stream is returned to process
would be paint baking or wire enamelling
ovens.
Figures 5A and 5B illustrate even more ela-
borate systems which, in addition to incor-
porating many of the previously mentioned
features, also supply a signal to the primary
process proportioned to the amount of im-
purity being evolved, so that more economic
operation of the primary process can be
realized.
IB!
A.
B.
CATALYTIC ELEMENT
AUXILIARY (START UP) BURNER
FIGURE 1
CONTAMINATED
STREAM
FUEL
BASIC' C'ATALYTIC
OXIDATION UNIT
-------
Catalytic Incineration Parameters and Operating Practices
B
FUEL
C'oni.:i mjiiatod
I,ow
Temp.
C'loan Stream Ai
High Temp.
(ean he used for
make1 up air)
A. Blower Motor
B. Blower (Mixer)
C. Fuel Burner
D. Catalytic Burner
E. Temperature Controller
FIGURE 2
Catalytic Oxidation
Low Temperature
Feed
d
B
FUEL
Clean
Contaminated
Stream
Stream
A. Blower Motor
B. Blower (Mixer)
C. Fuel Burner
D. Catalytic Elementl
E. Temperature Controller
F. Recycle Damper
G. Heat Exchanger
FIGURE 3
Catalytic Oxidation
Low Temp. Feed With
Recycle and Heat
Exchanger
-------
Catalytic Incineration Parameters and Operating Practices
CONTAMINATED
STREA iV
D
HOT CLEAN
STREAM
A Process
B Process Feed Gas
C Process Exhaust Gas
D Hot Clean Exhaust
E Pollution Abatement Equipment
FIGURE 4
Catalytic Oxidation
Recycle to Process
A
B
C
l_
Contaminated
Stream (500°F or
. Greater)
Clean
Stream
Signal to Alarm
A.
B.
C.
D.
E.
F.
Blower Motor
High Temperature Blower
Auxiliary Electric Heater
Catalyst Bed
Temperature Controller (Inlet Gas)
Temperature Controller (Outlet Gas)
Schematic Diagram
Engelhard Deoxair Purification System
FIGURE 5A
-------
Catalytic Incineration Parameters and Operating Practices
E
B
A. Blower Motor
B. Blower
C. Fuel Burner
D. Catalyst Bed
E. Temperature Controller (Feed Heater)
F. Temperature Controller (Process Controller)
Contaminated
.Stream
Clean
Stream
Control
SicnaJ To Process
Catalytic Oxidation
With Combustion
Analyzer Control
Signal For Process
FIGURE 5B
-------
THERMO OXIDATION OF GASEOUS
AND AEROSOL WASTE
Jim Eraser-
I INTRODUCTION
Thermo oxidation of gaseous and aerosol
waste is not a new concept having been used
for many years in limited manufacturing
processes. The deodorizing type air heater,
for example, was developed for use with
drying systems where vent gases had an
objectionable odor. However, this application
was always part of the process system and
was usually too large and costly to be thought
of as a deodorizer by itself.
In recent years a larger emphasis has been
placed on a more effective and practical
means of eliminating odorous air pollutants
through incineration methods. There is a
wide range of these odorous air pollutants
and they include most organic materials plus
inorganic combustibles such as ammonia,
hydrogen sulfide, hydrazine and cyanide
gases.
A few substituted hydrocarbons cannot be
effectively and economically oxidized to
materials suitable for discharge by methods
now available. These include certain halogen
compounds, metallic inorganics and organic
phosphates.
Odorous combustible gases are released
from a great many industrial processes.
A list of a few typical applications is given
below:
Chemical Processing
Resin manufacturing
Coil and strip coating
Fungicide and pharmaceutical
Carbon furnaces
Tar and asphalt blowing and coating
Bonding and burn-off
Rendering
With very few exceptions these fume streams
contain pollutant gases mixed with air in non-
flammable concentrations, that is, concen-
tration below the lower flammable limit. For
this reason they cannot simply be ignited or
flared. They may also contain certain
catalyst poisons or solid particles which rule
out low temperature or catalytic oxidation.
Therefore, it is necessary to heat them to
temperatures in the 1000 to 1500 degree F.
range in temperature for direct thermal
incineration.
II DESIGN PARAMETERS
The 1000 to 1500°F thermal incineration
range lends itself to a very practical and
economical all metal type incinerator such
as that designed and manufactured by the
UOP Air Correction Division which we will
be considering in the following design
parameters.
The design parameters must provide thorough
mixing of the combustibles with air. Enough
heat input to raise the temperature and gas
stream to the required level for oxidation,
even temperature and flow distribution and
sufficient dwell time at temperature to
accomplish the degree of oxidation required.
These conditions are met by supplying the
necessary temperature through a burner
firing into a holding chamber where oxidation
occurs. Actual design conditions for tem-
peratures and dwell times will differ
according to the reaction kinetics for the
particular pollutant present and combustion
efficiency required for odor cleaning. The
required dwell time is set by the size of the
holding chamber. The cross-sectional area
is normally fixed to give the desired linear
velocity and the length varied to obtain the
required dwell time. Because of economics,
systems are usually designed so that dwell
time does not exceed one second.
The reaction chamber temperature then
becomes the controlling variable and is
adjusted to obtain the desired combustion
efficiency. The mixing and distribution are
supplied by design features of the incinerator.
*Eastern Regional Manager, Air Correction Division,
Universal Oil Products, Greenwich, Connecticut
PA.C. ce. 39.1.67
-------
Thermo Oxidation of Gaseous and Aerosol Waste
We might also mention the fact that in many
applications, it is possible to add heat re-
covery equipment to the odor correction
system to reduce operating fuel costs. This
is a function of B. T. U. demand and fuel
savings versus the pay-out time for the
recovery equipment.
Ill PREHEAT BURNER
There are many reliable burner manufacturers
which can be considered for supplying equip-
ment. An important consideration is to get
a high turndown burner which will adjust to
requirements of the entire system. This
burner may be picked to burn various types of
fuel, the most common being natural gas or
oil. However, one point that should be stressed
here is that when oil fuel is picked, it should
be one with a low sulfur content that burns
without producing a lot of ash or sulfur
pollutants.
The burner size is a function of the desired
incineration temperature. The volume of the
fume stream handled and the thermal in-
efficiency of the system. Additional capacity
is sometimes added if it is anticipated that
more stringent combustion efficiencies will
be required in the future.
The outlet temperature will generally be re-
garded by air pollution control officials as
the primary measure of performance, with
all other phases of the operation normal to a
casual inspection, maintenance of a specified
outlet temperature will generally be accepted
as providing acceptable conversion level.
IV HEAT EXCHANGER
Of critical importance in the design of heat
exchangers is the handling of expansion and
contraction. Nearly all designs involve the
use of tubes or tubelike members. These
are supported between the tube sheets and
enclosed within a housing. The metal com-
prising the housing will ordinarily operate at a
different temperature than the tubes them-
selves. This requires that the sheets are
free to move relative to the housing. Careful
integration of the combustion chamber and
heat exchanger design is necessary to take
into account all the expansion factors.
Pressure drop and heat transfer rate are the
other critical variables in heat exchanger
design. The pressure drop on both sides
must be carefully calculated in order to
provide accurate information for fan selection.
The overall heat transfer coefficient must
be known to avoid oversizing the heat ex-
changer (for high combustible loads an over-
sized heat exchanger might mean an uncon-
trollable unit) and to insure that adequate
temperature levels may be sustained by the
burner.
V MATERIALS OF CONSTRUCTION
The odorous air pollutants encountered today
from industrial processes of which some
have been listed, can normally be incinerated
in the range of 1000 to 1500°F within the
design parameter discussed above. This
makes it possible to use easily available
metallic materials for incincraior and heat
exchanger construction and refractory
material is not normally required. This has
a 2-fold advantage. First, the ease and
economics of fabrication which allows for
ease in handling and transportation of the
equipment. Second, the light weight materials
make it possible to install this equipment
where weight limitations are imposed such
as roof tops, etc. However, it is very im-
portant that good engineering design be
followed to accommodate for thermal expansion
and gas distribution in the all metal construction.
The heat exchanger also forms a vital part of
the thermal incineration system regarding
materials of construction. It reduces the
exit temperature to a level where ordinary
steel may be used for the ductwork and stack.
The heat exchanger may be constructed of
stainless steel; or if the tube walls and tube
sheets are properly handled, of carbon steel.
Even where the hot gas temperature exceeds
the usual temperature limits for carbon steel,
aluminized steels are available for tubewall
design temperature up to 1200°F.
-------
Thermo Oxidation of Gaseous and Aerosol Waste
VI INSTRUMENTATION REQUIREMENTS
Instrumentation burner control, safety con-
trol and wiring used in the thermal incinerator
are of the same type as conventionally used
in ovens and dryers and set up by the insur-
ance underwriters covering the operation on
which the equipment will be installed.
Process gases are maintained at the desired
temperature by controlling the preheat burner.
As the temperature, volume and combustible
concentration of the fume stream varies, the
burner input is automatically adjusted pro-
portionately. An independent high and/or
hi-low temperature indicating alarm controller
is also incorporated in the instrumentation to
protect against extreme temperature condi-
tions. The incinerator will automatically shut
down and divert through a bypass to the ex-
haust stack.
The auxiliary equipment used for heat re-
covery is again controlled using approved
control circuits and equipment. The recovery
train is custom designed and the controls will
vary depending on the particular application
for which the recovery will be applied.
VII OPERATING CONDITIONS
In most air correction problems, the fume
stream will carry sufficient oxygen to be
used as a source of secondary air allowing
the burner to operate at stochiometric pro-
portions or less primary air. However, in
some cases it is necessary to add excess
primary air in amounts up to 5 percent if the
fume stream has a large percentage of inerts
and consequently, minimum oxygen. Since
the fume stream has to be heated to the re-
action for air pollution control, it provides
an economic source of secondary combustion
air. Any primary air added must be heated
to the reaction temperature and adds to the
operating cost. Excess primary air has
little influence on the combustion efficiency
and wastes fuel.
VIII RATE OF REACTION
The kinetic theory of gases in relation to the
rate of reaction of variables such as time,
temperature and degree of reaction is not a
clear cut proposition. If sufficient background
data and fume analysis is not available, pilot
tests or source tests have to be conducted
on the fume stream to determine this reaction
rate.
The design of equipment for the primary
purpose of odor elimination is not simply a
matter of reducing total pollutant concentra-
tion to some arbitrary level. Different gases
and vapors have different odor thresholds.
To complicate the problem still further, a
mixture of materials will usually have a
different odor threshold than any of the
individual components. Because most indus-
trial exhaust gases contain mixtures of pollu-
tants and because these mixtures vary greatly
from one process to another, it is frequently
necessary to run pilot or laboratory tests to
determine the degree of cleanup necessary to
accomplish odor freedom. Much of this vita]
data has been correlated by our source testing
department, from which practical and economi-
cal system design is obtained. It has been
found in many cases a typical reaction rate
can be utilized for common air pollutants.
Various air pollution control authorities have
set up design standards of their own. For
example, the Engineering Department of the
Los Angeles Air Pollution Control District
requires that all thermal incinerators be
designed for a fume stream velocity of 40
f. p. s. and at least 0. 6 sec. residence time,
having the ability to operate in the temperature
range of 1500°F.
IX SUMMARY
In conclusion, odor elimination can be accom-
plished effectively by thermo oxidation in
nearly all cases where combustible gases
and aerosol waste are involved.
The importance of the basic design parameters
should not be underestimated and to review,
these are: through mixing of the combustibles
with air, even temperature and flow distribu-
tion, high enough temperature, and sufficient
dwell time. By proper selection of these
parameters through reliable fume stream
analysis, pollutant destruction closely
approaching 100 percent can be achieved.
-------
CONTROLLED ENDO-EXOTHERMIC OXIDATION
OF INDUSTRIAL WASTES
Robert D. Reed*
Uncontrolled venting of waste gases and
liquids to the atmosphere and to the water-
ways of the world which once was an accepted
way of life in industry is no longer to be
tolerated and is rapidly becoming illegal.
Cost for means to avoid air and stream
pollution is, at times, considered awe-inspir-
ing according to the nature of the materials
for disposal. In fact, necessity for avoidance
of pollution in any respect may well be the
determining factor in choice of plant location
according to local ordinances or pollution
regulations.
Fuel demand for satisfactory disposal is
entirely governed by the nature of the gases
or liquids for disposal. If no means for heat
recovery .are to be provided the fuel cost
represents a complete loss except for the
fact that the cost is an operating expense
and represents means for some tax relief.
Capital expense of erection of means for
disposal is significant in any case. The
total capital expenditure is also governed by
the nature of the products for disposal as
well as local regulations for control of
pollution. Separate studies of disposal
problems should be made in each case with
the study to take into careful consideration
minimum acceptable standards for the
service as required.
The separate and careful studies are
suggested because there is ample history of
under-designed facilities causing great
financial loss as well as embarrassment
where lack of knowledge of the problem in
all details as well as reluctance to make a
suitable capital expenditure may be
considered as causes.
Where endo-exothermic oxidation is the
means to the end of disposal of waste matter,
the end-products required are those of
complete oxidation. Any matter which
contains elements which are subject to oxi-
dation in exposure to adequate temperature
level for a great enough length of time is
subject to such disposal means whether it
be in the liquid or the gaseous phase.
Requirement for such disposal means must
be based on the design temperature level,
great enough residence at the design tempera-
ture level, a suitable condition of controlled
turbulence and the presence of adequate
quantities of oxygen. It is, perhaps, a bit
disconcerting to consider that carbon tetra-
chloride (CC 1 ) held at 1800°F (982. 22°C)
A
for a period of 5 seconds and in the presence
of oxygen is converted to CC>2 + 2 Cl2 in a
series of reactions which terminate in an
exothermic state.
Thus the factors time, temperature and tur-
bulence which are classic for the burning of
fuels become factors in disposal by oxidation.
However, there are equally important
supplementary factors which also must be
considered.
Experience shows clearly that the auto-igni-
tion temperatures of disposal products are
of small concern. Experience shows equally
clearly that the deciding factor for design
temperature level for speed of oxidation with
any fuel can best be stated as one of mole-
cular proximity. In this sense the proximity
of molecules of fuel to molecules of oxygen
governs.
In the case of a stoichiometric mixture of
air and methane (CH4) where both methane
and air are dry. there will be approximately
18. 92% oxygen, 9. 46% CH4 and 71. 62%
nitrogen. Under normal conditions this
mixture will burn in approximately 10 milli-
seconds at 1500°F environmental temperature.
This speed of burning is established by the
molecular proximity of oxygen to mcthnne
typical of this mixture or the readiness of
combination as based on typical molecular
dispersion in a homogeneous mixture such
as this.
*Vice President, Engineering, John Zink Company,
Tulsa, Oklahoma.
PA.C. ce. 12.5. 66
-------
Controlled Endo-Exothermic Oxidation of Industrial Wastes
If, however, the methane should be diluted
with nitrogen so that there is only 2% methane
in the methane-nitrogen fuel and if this fuel
should be mixed homogeneously with air in
stoichiometric mixture the burning time
would be very greatly increased because of
reduction in proximity of oxygen to CH4 in
the mixture and the burning time would now
be approximately 0. 32 seconds AFTER the
time required to elevate the temperature of
the fuel-air mixture to auto-ignition tempera-
ture to produce an observed burning time
very close to 1 second at environmental
temperature of 1500°F.
If the dilution of the fuel with inert matter is
carried further, burning times at 1500°F
begin to be tremendous and the cost of a
structure for disposal to provide the required
time at 1500°F goes far beyond economic
limits. Fortunately the equations of
arrhenius in point of the effect of temperature
On reaction velocities provide a very suitable
solution for this problem but at the expense
of greater fuel demand.
Where there is 1% or less of burnable toxic
or noxious matter in a stream of otherwise
inert material experience shows clearly
that design temperature in the order of from
1800°F to 20006F with a time factor of from
3 to 5 seconds will be required to secure
complete oxidation in the presence of not
less than 25% excess air.
At this point, it becomes expedient to more
comprehensively define the term "complete
combustion" or oxidation of fuel. In the
typical practice of burning fuels for produc-
tion of useful heat, combustion is considered
complete when the Orsat or the electrical
flue gas analyzer shows absence of combus-
tibles in the gases following burning. How-
ever, these devices are seldom capable of
accuracy better than 0. 05%. With accuracy
at 0. 05% there could be as much as 500 ppm
of the toxic or noxious material in the flue
gases following the burning period. Com-
plete combustion, as we define it, does not
exist in this case.
It is true that thermal rise and exit velocity
effects will produce dilution of the stack
gases so that as the gases reach grade down-
wind of the stack, the concentration of toxic
materials may be reduced to tolerable limits
for most toxic or noxious materials with
dilution obtained through selection of proper
stack height. There are standard calcula-
tion methods for determination of stack height
to obtain the required dilution. However,
the formulation contains both empirical and
judgment factors which may introduce error
to a greater or lesser degree.
Average target concentration at grade and
downwind of the stack is in the order of
0. 10 ppm or perhaps less. For most toxic
or noxious substances this concentration is
satisfactory; however, there are many
substances where this small concentration
is far too great and severe odor or health
nuisance is created. A further hazard is
the tendency for products not present in the
disposal stream to be synthesized in the
course of passage through the furnace. These
products can be alcohols, aldehydes,
organic-sulphur compounds and others.
It is interesting to note that according to
the Manual of Disposal of Refinery Wastes,
Volume II, Waste Gases and Particulate
Matter as published by the American
Petroleum Institute the following substances
will cause odor nuisance in concentrations
as shown.
Iso-butyl alcohol
Iso-amyl alcohol
Methyl mercaptan
Ethyl mercaptan
nPropyl mercaptan
nButyl mercaptan
Iso-amyl mercaptan
pThiocresol
Methyl sulphide
Ethyl sulphide
Propyl sulphide
nButyl sulphide
.003 ppm
.0026 ppm
. 041 ppm
. 0028 ppm
.0016 ppm
. 001 ppm
. 00043 ppm
. 0027 ppm
. 0037 ppm
. 000056 ppm
.011 ppm
.015 ppm
-------
Controlled Endo-Exothermic Oxidation of Industrial Wa:
It is considered in order to question the
absolute accuracy in measurement of such
tiny concentrations; however, if the accuracy
is only 50% odor nuisance will still exist. In
the "blowing" of hot asphalt to improve the
characteristics of the asphalt through partial
oxidation, the gases contain odorants and
while there is no definition of odor perception
levels for these compounds in the literature
there is mounting evidence that concentrations
in the order of 0. 01 ppm are capable of
creation of odor nuisance.
Various researches*1* which have not been
reported into the literature have shown that
in the burning of compounds containing sul-
phur from 10 weight per cent to 25 weight
per cent of the sulphur will appear in the
stack gases as 803 when the burning has
been carried out in a refractory lined furnace.
The remainder of the sulphur is as SO2. The
influence of SO3 on the dew point character-
istics of combustion gases is such that dew
point occurs immediately after departure
from the stack to produce a light gray-blue
"smoke" of sub-micron size particles of 803.
The particles are small enough to be air-
colloid. Such "smoke" diffuses very poorly
and, from an airplane, has been observed^
in travel over more than 75 miles from the
point of origin of the "smoke" to disappear
into the haze in the distance. This phenom-
enon was observed in a very dry climate
and at mean ground altitude of 4000 feet with
ground wind velocity at approximately 20 MPH.
In disposal of liquid streams the residence
time factor must provide for the time inter-
val required for conversion of the liquid to
the gaseous state. This can be quite appreci-
able. Also in disposal of liquid streams and
when mineral salts are present it has been
repeatedly shown that the mineral exists
from the furnace in the form of its oxide and
as sub-micron size particles which also are
air-colloid to appear at the stack as "smoke. '
In one particular instance where there was
approximately 5 weight per cent of sodium
acetate in the liquid stream for disposal and
at 1800°F there was very little accumulation
of mineral residue within the furnace after
a period of approximately G months. In this
case the waste stream was approximately
5 gpm continuously for the period of opera-
tion. Also in this case there was no report
of hazard or damage due to the gas carried
particles of sodium oxide. Operation has
continued safely and without incident for a
number of years. Operation of the furnace
at excess air in the order of 175% completely
suppresses any tendency for the mineral
oxides to appear as "smoke. "
The fuel cost factor for disposal is subject
to considerable relief if suitable heat re-
covery systems follrw the disposal system;
however, the business of heat recovery
must not be allowed to interfere with com-
plete burning. Heat recovery can be as
steam generation; heating of process
materials or air-preheat, but the recovery
means must suit the disposal problem and
must be chosen according to the nature of
the problem.
REFERENCE
1 Private communications, John Zink
Company.
-------
FLARE COMBUSTION
LeonardC. 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.
Air Pollution can result from flare combus-
tion. As we realize, pollution implies an
adverse ecological situation. Air being
man's universal and most vital environment
makes the control of air pollution a major
responsibility of The Public Health
Profession.
A survey would indicate that air pollution
means different things to people. However,
all of these meanings can be placed in one
of three categories, namely:
A Adverse effects upon our health
B Nuisance irritation to our basic senses
C Economic loss
These affects may occur singularly or in
various combinations with each other.
Experience has shown that the slightest
unwanted change in the air causes great
consternation among people. We have
become accustomed to expect certain things
from the air: that is, odorless, tasteless,
and invisible - that it should be neutral
in regard to its physical and bio-chemical
effects. Further, air is expected to fulfill
certain requirements that relate to our
well-being and enjoyment, namely:
When respired, air will effect the
metabolic needs for our activities without
adverse physiological consequences of
either an acute or chronic nature.
That air not be offensive to our basic
senses of hearing, seeing, feeling,
tasting or smelling.
That air not cause damage to our property,
be it buildings, furniture, automobiles,
livestock, vegetation, or other physical
or animal assets - all of which would
result in economic loss.
Accordingly, anything that modifies the
nature of air as we have learned to know
and enjoy it, may be called an Air Pollutant.
Flares may rightly be classed as significant,
potential sources of local pollution because
they can emit gases that are not only toxic
but that can cause property damage, person-
al injury, nuisance and psychosomatic illness.
*Consulting Engineer, Leonard C. Mandell Associates,
66 Pitman Street, Providence, Rhode Island.
PA. C. ce. 38. 1. 67
-------
Flare Combustion
may evolve from the nature of
the raw vent gases - - as the highly
dangerous carbonyl chlorides and phthalic
anhydrides, chlorine, hydrogen cyanide
-- or from products of incomplete incom-
bustion as phenols, aldehydes, organic
acids, or from products of complete
combustion as sulfur oxides and hydro-
chloric acid vapors.
Property damage may vary from being
rather apparent as soiling from soot/ smoke
or heat-damage from radiant flames- or
more subtle as from corrosive damage of
sulfur trioxide, mist- size aerosols.
Personal injury may occur from falling
and burning liquid aerosols that somehow
should not have arrived at the burner- tin
for flaring. '
The nuisance aspect is excellently brought
out by the odor problem from say hydrogen
sulfide or the organic mercaptans. It
should be noted that noise is also becom-
ing a problem -- especially with high,
specific steam ratios.
The psychosomatic aspect can be involved
with ones knowledge of just the presence
of the Hare, (in his effective environment)
whether it is creating an invisible-plume
or a smokey, sunlight obscuring plume.
Hence, it behooves the "operators" to
minimize these effects - any of which can
cause not only poor community relations but
even costly litigation. It has been the author's
experience that, as a rule, industry is
desirous of being a good neighbor and will
do the right thing if shown the need and if
properly handled.
II BASIC THERMODYNAMICS
It should be noted that very few if any text-
books on combustion or thermodynamics con-
tain any information on flares -- not
withstanding the fact that successful flare-
burning is a highly-specialized thermodynamic
combustion process. Perhaps, the reasons
are that the universal need for Hares is
relatively very small and what information
has been learned is treated as proprietary -
and so kept confidential for business reasons
III COMBUSTION - In General:
Any combustion gas can be completely
oxidized if exposed to an adequately high
temperature level for a long period of
time in an atmosphere of sufficient oxycen
and turbulence.
For purposes of this lecture let us look at
combustion as a continuous, highly-complex,
high-temperature, gas-phase oxidation
process with very specific characteristics
namely:
A It involves a very rapid chemical reaction
between the elements and compounds of
hydrogen, carbon and sulfur and the
oxygen in the air.
That this reaction in order to be rapid
enough requires fuel/air mixture temper-
atures much higher than the conventional
ambient of 70°F, and within definite
ranges of concentrations for various
combustible compounds.
B
C That concurrent heat energy will for the
most part be liberated and/or occasionally
be required by the reaction to maintain
its continuity. The common oxidation
reactions of carbon, hydrogen and sulfur
are exothermic liberating 14, 500 BTU'S
and 4000 BTU'S per Ib. solid of carbon and
sulfur, and 61, OOOBTU'S/lb. of gaseous
hydrogen respectively.
The water-gas reactions of:
C +
H20- CO + H2
2 C
2H20
C0 + 2H
These reactions
are quite rapid
at temperatures
greater than
1650°F.
require heat inputs of approximately
5900-6000 BTU/lb. carbon.
-------
Flare Combustion
D That the combustion process requires
close control of adequacy and intimacy of
contact between the gas fuel and the
oxygen molecules in order to obtain
complete combustion; otherwise undesir-
able pollutants such as soot, smoke,
aldehydes and carbon monoxide, etc. will
be formed.
E That the reaction occurs with presence
of a luminous flame. Certain Basic
Concepts must be understood:
L. E. L. or Lower Explosive Limit or
lower inflammable limit: This is the
leanest mixture (minimum concentration)
of the gas-in-air which will support
combustion (where flame propagation
occurs on contact with an ignition source).
U. E. L. or Upper Explosive Limit: This
is the richest (Maximum proportion) of
the gas in air which will propagate a
flame.
Autogenous Ignition Temperature or
Auto Ignition Temperature: The minimum
temperature at which combustion can be
initiated:
It is not a property of the fuel but of the
fuel/air system. It occurs when the rate
of heat gain from the reaction is greater
than the rate of heat loss so that self-
sustained combustion occurs.
Flame Propagation - The speed at which
a flame will spread through a combustible
gas-air mixture from its ignition source,
it is usually lower at L. E. L. and the
U. E. L. , and higher at the middle of
range.
Flame: A mass of intensely, heated
gas in a state of combustion whose
luminosity is due to the presence of
unconsumed, incandescent, fractional-
sized, particles - mainly carbon. (Small
particles of suspended carbon/soot formed
by cracking of hydrocarbons). Visibility
ceases at complete combustion or where
the glow of the ash ceases.
Infra Red Radiation: Is, for the most
part an invisible, electromagnetic
phenomena. Relatively large amounts
of heat are radiated at elevated tempera-
tures by such gases as carbon dioxide,
water vapor, sulfur trioxide, and hydro-
gen chloride. The I. R. spectrum begins
at 0. 1 micron wave length and extends up
to 100 microns. For reference, I. R.
solar radiation (10, 240°F) lies within
the 0. 1 to 3 micron range. (We know
that a large proportion is emitted in the
visible band of 0. 4 to 0. 8 micron. A
2300°F black body emits most of its
energy between 0. 7 and 40 microns. For
the discussion at hand, (temps between
1500 and 2500°F) radiant emission may
be assumed between 0. 5 micron and 50
microns with maximum intensity occur -
ringatthe2 micron wave-length.
Timing is important in that the attainment
of satisfactory combustion requires
sufficient, high-ambient, reaction
temperatures, and an adequate oxygen-
fuel mixing. Both phenomena are related
to time/probability functions.
IV BASIC COMBUSTION CONCEPTS AS
APPLIED TO FLARES:
A Gaseous fuels alone are flared because
they:
Burn rapidly with very low percentage
of excess air resulting in high flame
temperatures.
Leave little or no ash residue.
Are adaptable to automatic control.
B 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 (C2H2)
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.
-------
Flare Combustion
Ethane (C2H6) with a H/C r 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.
C In flare burning of sulfur-bear ing com-
pounds: approximately 90% or more
appears as sulfur dioxide and 10-30% of
the (SO2> mutually appears as sulfur
trioxide. Blue grey smoke becomes
visible as the sulfur trioxide falls below
its dew point temperature.
D In flare burning of chlorine-bear ing
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.
Atll50°FAIT: A minimum H. V. of
350 BTU/ cu. ft. is required.
At 1300°F AIT: A minimum H. V.
500 BTU/cu. ft. is required.
of
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 Actual Flare Burning Experience (John
Zink Company)
(Dilution/ Temperature Effects for
acetylene in air)
@1800°F temperature will burn com-
pletely in 0. Oil sec -- 50% Dilution
C2H2 @ 1800°F temperature will burn com-
pletely in .016 sec. -- 75% Dilution
C2H2 @ 1800°F temperature will burn
completely in .034 sec --90% Dilution
C2H2 @ 1800°F temperature will burn com-
pletely in .079 sec --95% Dilution
F Since the heat content of many gases vary
much below 100 BTU/cu. ft. and since
@ 1800°F temperature will burn com-
pletely in 1. 09 sec --99% Dilution
C2H2 @ 1800°F temperature will burn com-
pletely in 4. 08 sec --99. 5% Dilution
Note: The 4. 08 sec. time @ 1800°F falls to
less than 1 sec. @ 2000°F temperature.
J Flared gases must be kept at temperatures
equal to or greater than auto ignition
temperature until combustion is complete.
K Carbon monoxide burns rapidly with high
heat and flame temperature, whereas
carbon burns relatively slow.
-------
Flare Combustion
L 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) Stearn 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.
M 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.
N Water sprays, although effective in low-
profile, ground-flares, have not been
effective to date in elevated Hares. 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.
Note: Recent water shortages dictate the use
of steam since specific water wastes of
1-2 Ibs. water/lb. of gas is customary.
Approximately 2-3 times as much
water as steam is needed for ground-
level flaring.
O The following table summarizes some
pertinent gas characteristics for flaring.
GAS PROPERTIES RE-FLARING
Element/
Compound
H2
C2H2
NH3
H2S
CO
C3H8
CH4
HCN
C
S
C2H4
C4H6
Mol.
Wt.
2
26
17
34
28
44
16
28
54
II
H/C AIT
1000-llOOOp
.083 600- SOOOp
1200
550- 700
1200
.222 1000-1100
.33
1000
750°
470°
. 17
. 13
% by Vol.
LEL
4. 1
2.5
16
4. 3
12.5
2. 1
5.3
3
2
in Air"
UEL
74
80
27
46
74
11.4
14.0
29
11.5
Btu/cu.
ft.. Net
275
1435
365
596
321
2360
914
1512
2840
Flame Flame
TemD-°F =;n<=eri
4100°F l-16'/Sec
4200 2-5
4200 1-4
3800 .8-2.2
-------
Flare Combustion
V TYPES OF FLARES:
Flares are arbitrarily classed by the elevation
at which the burning occurs; i. e. -- The
elevated-flare, 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.
A 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.
Note: Rothschild Oil built a 2, 000, 000 Scfd
(standard cubic feet per day unit) in 1953
for $5,000.00.
B Ground Flares: In general, ground flares
require approximately 2l/i 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.
Typical water spray flare-design
requirements are;
The spray must intimately mix with
the burning gases
These gases require an outer shell to
retain heat and flame.
Combustion air of at least 150% must
be allowed to enter the base through
the surrounding shells. The higher the
molecular weight of the gas, the
greater the spray rate: Example:
200,000 Scfhr. M. wt. : 28 30-40 psig.
@35 gpm.
is required.
200, 000 Scfhr. M. wt. = 37 120 psig,@
80 gpm.
is required.
Back in 1959, Esso Research developed
the Multi-Jet Flare. It operates in a
smokeless and non-luminous manner
with very little noise. The flare requires
little of the conventional auxiliaries. It
consisted of a series of rows of horizontal
pipes containing 1 inch diameter jets that
served as burners. These burners were
located at the base of the stack approxi-
mately 2 ft. above ground level. The jets
require flame-holders (rods) to provide
time and turbulence for adequate air-mixing
-------
Flare Combustion
for smokeless combustion. A 32 ft. high
stack was required to shield the flame.
A 3 ft. diameter flare handled up to
140, 000 standard cubic feet per day and
a 6 ft. diameter stack up to 600, 000 Scf /
day. It operated with a 25 ft. high flame.
A cost comparison with other flares
types at that time was made: - Based on
12, 000, 000 Scf/day of a 40 Mol. wt. gas,
the multi-jet cost $148,000. This was
twice the cost of an elevated flare without
steam, or one half the cost of an elevated
flare with steam. This was also about
the same cost as a ground-flare with
water.
C 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 flare
may or may not operate smokelessly.
Elevated flares require special burner
tips, special pilots and igniters, wind
screens, refractory lining, and instru-
mentation--for acceptable performances.
Let us take a moment and review what
happens at the flare-tip.
HAPPENINGS AT THE FLARE TIP:
2 ROWS OF
SUBORDINATE PORTS
FLARED GASES
TO ATMOSPHERE
PILOT TIP
STEAM
FLAME FRONT
IGNITER-TIP
IGNITER
•-TUBE
SUPPLY
RISER
COOLING
AIR-UP
PRE-MIXED
PILOT
GAS-AIR MIXTURE
-• DIAMETER SIZE OF FLARE
-------
Flare Combustion
Gas is ignited just as it reaches the top
of the stack. Before adequate oxygen/fuel
mixing can occur throughout the entire
gas profile certain things occur:
Part of the gas burns immediately
resulting in an oxygen deficiency which
induces carbon-formation.
The unburned-gases crack to form
smaller olefins and paraffins; and at
the same time some molecules poly-
merize to longer chain hydrocarbons.
More carbon is created from combus-
tion of these newly formed compounds
in a reducing atmosphere.
The long, luminous-flame in ordinary
flaring is made up of incandescent,
carbon particles which form smoke
upon cooling. Steam-mixing suppresses
carbon formation by:
a) Separating the hydrocarbon mole-
cules, thereby minimizing
polymerization.
b) Simultaneously forming oxygenated
compounds which burn at a reduced
rate/temperature not conducive to
cracking/polymerization.
Note: The absence of incandescent carbon
also gives the appearance of a shorter
flame.
That the idea of injecting water/steam
into flares originated at Esso Refinery
in Everett, Massachusetts.
VI TYPICAL DESIGN CONSIDERATIONS AND
PARAMETERS
B Capacity must handle the maximum
expected quantity if toxic, or a statistical
compromise of the maximum expected
release. This may indicate normal
operation of 1-5% of these capacities.
C Pilots must be stable in high winds (80 mph)
and heavy rains.
D Pilots must be ignitable in high winds
(80 mph) and heavy rains.
E The height of the flare is determined
by fire and heat safety. Dilution may
also be important from an air pollution
standpoint.
F Steam requirements are related to the
H/C ratio (wt.). For H/C ratios greater
than 0. 33 - no steam is needed. Lower
ratios can demand up to 2 Ibs. steam/lb.
of vent-gas to obtain smokeless operation.
As a rule, 0. 6 Ib/lb. appears to be the
average required. Steam requirements
are proportional to the degree of
unsaturation and the molecular weight
of the gas being flared. Flares are
designed to be smokeless for up to 15%
of capacity only.
G Sizes may vary from 1^ inch pipe to
120 inch diameter.
H The burning rate can vary from 0. 5% -
100% of design.
I Systems up to 1, 000, 000 Ib/hr. of 43 mol.
wt. @ 700°F have been flared. (Zink)
J Typical data for hydrogen sulfide flares
would appear as follows:
A Ignition and stable-burning must be
insured.
-------
Flare Combustion
DATA
Ibs/hr:
cfm
cfday
flare size
cost installed
type
steam
flame dimensions
Ht. above ground
to negate heat
effects from flame
SIZE OF FLAME
600 Ibs/hr.
112 cfm
164,000 of day
2 inch diameter
$2300
non smoking
no1
10 ft. ht. X 1 ft. diam.
50 inch*
10,000 Ibs/hr
1900 cfm
2, 750,000 cf day
12 inch diameter
$5800
non smoking
no'
40 ft. long X 3 ft. diam.
85 inch*
* May be much higher for air pollution control.
K It should be noted that radiant, flame
effects can be serious. Radiation and
solar heating should not exceed 1000
BTU/Hr./Sq. Ft. at ground level with
700 BTU/Hr./Sq. Ft. from the flame and
300 from the sun. (Zink)
L The igniters operates only to start the
pilot. The pilot burns continuously. A
2-3 inch diameter flare requires one pilot.
A 4-6 inch diameter flare requires two
pilots and Hares greater than 6 inch dia-
meter requires three pilots.
M Auxiliary heat is needed for gases with
lower heating values of from 50-100 BTU/
cu. ft.
N Flare heights range from 25-375 ft. with
flame radiation being the determining
factor.
O Hydrogen, carbon monoxide, and ammonia
burn smokelessly without assistance.
P Tendency for smoking begins at H/C of
0. 25 and becomes heavy @H/C of 0. 20.
Q In general, flare operation of gases less
than 150 BTU/cu. ft. heat content becomes
quite critical in point of maintenance
of ignition in all-weather conditions.
Here endothermic design is needed. Only
very few are in use. Usually they are
limited by economics to sizes less than
5, 000, 000 BTU/hr equivalent of
auxiliary fuel.
R Steam may also be required for preheating
in very cold areas -- besides being
needed for smoke control.
VII AUXILIARIES REQUIRED FOR SUCCESS-
FUL FLARE OPERATIONS:
A Flare Tips of Inconel or other stainless
alloys with steam jets, air cooling,
stabilizing parts, etc.
B Ignitors are used to light the pilot at
start-up or at Pilot name failure.
C Pilot Burners to light flare and keep it
lit
D Mist Trap: to remove fine, liquid aerosols
from reaching the stack.
E Flame arrestor: to prevent flame-travel
back into piping.
F Liquid seal: To reduce pulsations from
surges: to prevent air from entering
vent-gas lines: to prevent reverse-name,
flash-back.
G Flow Sensors for steam control
H Pilot flame detectors
I Auto reignition system for pilots
-------
Flare Combustion
J Shrouds are not of real value in smoke
control, however, they can be used in
preventing downwash.
Note: The pilots initiate combustion of the
flared gases. They also help to heat
and maintain flame temps. The ig-
nition system consists of premixed
15 psig. fuel gas/air mixture that is
pre-ignited in a special in-line, pipe-
chamber by a spark plug. The flame-
front, under flow-pressure, travels
through a 1 inch igniter pipe to the
tip of the pilot burner. Once the pilot
is ignited, the fuel and air valves are
closed. Time for ignition of all 3
pilots averages 1-2 minutes. Pilots
must burn at a rate of at least
30,000 BTU/hr. each.
VIII MATERIALS OF CONSTRUCTION:
Reflection will indicate that many flare-gases
are corrosive at normal atmosphere temper-
atures. Chemical activity, as a rule,
increases with increasing temperatures.
Hence, the selection of suitable materials
for the handling/conveying of these gases
-- especially at the flare-tip becomes signi-
ficant to the feasibleness of this particular
method of combustible, gas disposal.
It should be remembered that metals or
alloys provide the function of corrosion-
resistance by either formation of a surface
film or resistance to chemical activity with
the environmental materials. Accordingly,
other corrosive factors as gas velocity,
thermal shock and catalytic influences must
be considered in addition to temperature
effects. Another practical consideration
is the deleterious carbide precipitation that
results from the welding process. It removes
some of the corrosion resistant and strength
constituents from the alloy.
The stainless-steel, iron alloys (approxi-
mately 74% steel) are at present, the most
feasible metals for flare construction. The
stainless steels compose a class of nickel
and chrominum alloys that owe their
corrosion resistance to the high metal content
and the strength to the chromium. Tenacious,
protective film develops especially
in oxidizing atmosphere. Typical stainless
compositions are:
ALLOY % Cr
TYPICAL STAINLESS STEEL ALLOYS
% Ni % C % Mo % Si
% Mu
Co
304
316
347
430
Hastelloy
Inconel
(6% Fe)
18-20
16-18
17-19
14-18
's X
10
8-10
10-14
9-12
X
84
. 08 max.
.10 2-3
.10
. 12
X
. 75 max.
. 75 max.
. 75 max.
. 75 max.
2.
2.
2.
0.
0
0
0
max.
max.
max. 1. 0% max
50
10
-------
Flare Combustion
Leading suppliers of special stainless steels
are International Nickel Company; Haynes
Stellite. Division of Union Carbide; Carpenter
Steels, etc.
Experience has shown that:
Type 304 s. steel is satisfactory for
1600 F -sulfur exposure
Type 309 s. steel is satisfactory for
2000°F -sulfur exposure
Inconel - a high heat resistant alloy for
hydrogen sulfide, but not sat-
isfactory for hydrogen chloride,
sulfur dioxide or sulfuric acid
vapors.
Hastelloy - (special s. steel) manufac-
tured by Haynes Stellite is
good for SO3, H2SO4 and Hcl.
Hastelloy B for chlorine resistance
H2S04
Hastelloy A for Hcl,
, SOg, H2SO
In the final analysis of material selection.
the cost of replacement must be carefully
weighed against the longer life and higher
initial cost of the most resistant materials.
REFERENCES
1 American Petroleum Institute, N. Y.
Manual on Disposal of Refinery Wastes,
Volume II Waste Gases and Particulate
Matter, 1957.
2 Reed, Robert D. John Fink Co. , Tulsa,
Oklahoma, Private Communications,
1966.
3 Smith, Richard H. J. Arthur Moore Co. ,
N. Y. C., Private Communications.
1966.
4 The Various Petroleum Companies, (such
as Shell, Esso, Gulf) Research and
Engineering Departments.
5 Petroleum Processing Journals.
Type 430 is suitable for general use up
to 1600°F
11
-------
FLARE BURNING OF WASTE GASES
Robert D. Reed*
Flare design for safe and satisfactory dis-
posal of waste gases is far more important
in point of avoidance of air pollution than
would normally be considered.
Abatement of air pollution would require that
all the components of the waste gases not only
be subject to complete oxidation by burning
but that the flare must be capable of complete
oxidation of such gases as are directed to the
flare.
Compounds which completely oxidize to CO2
and H2O are many. Some are as follows:
Paraffins
Iso-Paraffins
Olefins
Diolefins
Alcohols
Glycerols
Carbon Monoxide
Acetylenes
Olef in-Acetylenes
Aromatics
Cyclo-Paraffins
Glycols
Ketones
Hydrogen
Many of these compounds when only partly
oxidized form highly toxic compounds such
as phenol, formaldehyde, acidic anhydrides
and others. Thus the flare must be capable
of accepting and completely oxidizing any
gas which is delivered to it.
Flared gases which contain sulphur or
chlorine in one form or another such as the
following are serious in point of air pollution:
Hydrogen Sulphide
Organic Sulphides
Carbonyl Chloride
Sewage Disposal Gases
Mercaptans
Carbonyl Sulphide
Organic Chloride
It is to be seen, then, that the flare design
must provide not only for as nearly as pos-
sible completion of combustion but the height
and thermal rise following burning must be
such as to diffuse the toxic SO2-SO3, Cl 2
and HC1 resulting from complete burning
to non-toxic concentrations as the combustion
gases return to grade.
Note that according to proprietary research
which has been repeatedly verified and in
flare burning of sulphur-bearing compounds
approximately 10% of the sulphur weight will
appear in the combustion gases as SO3 and
not necessarily as SO9.
Again in cases of proprietary research most
of the chlorine will appear as HC1 but in all
cases an appreciable portion of the chlorine
will appear as Cl 2- Neither will be corrosive
in the absence of hydration or wetting but
wetting is possible in most cases due to
dew-point of hydrogen-burning which accom-
panies production of products of oxidation,
as well as rain.
Thus corrosion hazard adds to the problems
of complete burning; of diffusion of products
following burning and consideration of the
flare location in view of prevailing winds.
Resistance to anticipated corrosion or corro-
sive conditions must be based on the flare
metallurgy. There is rather a wide choice
of metals for these conditions but there is
yet another consideration in flare design
which is the ability of the metals as chosen
to resist heat attack.
Flare structure metals must be wisely chosen
for the conditions which arc to exist at the
point of burning of the flared gases.
The Series 300 steels (304, 309 and 310) re-
sist heat attack well in the temperature
range of from 1600°F to 2000°F but all arc
subject to Sigma-Phase embrittlement in
continued exposure to heat.
The 300 steels resist attack of elemental
sulphur to varying degrees at elevated
temperature levels.
*Vice President, Engineering, John Zink Company, Tulsa, Oklahoma.
PA.C.ce. 13. 5. 66
-------
Flare-Burning of Waste Gases
Note the emphasis on elemental sulphur as
distinguished from oxides of sulphur which
have little more effect on steels than oxides
of carbon. When the metal is exposed to
H2S, Mercaptans, Organic Sulphides,
Carbonyl Sulphide and others, dissociated
sulphur as such does attack the metal at high
temperature levels.
The rate or magnitude of the attack seems to
be governed by the percentage of nickel pre-
sent in the alloy, thus of the 300 steels the
304 and 309 are superior to 310 at any temp-
erature condition but the 304 is suitable for
temperature limited to 1600°F, whereas 309
is suitable for 2000°F.
Series 300 steels are the metals of choice if
resistance to sulphur attack governs but the
metallurgy for chlorine attack is quite
different. For such conditions of corrosion
the metals of choice are Hastelloy B, Monel,
Inconel, Incolloy, Titanium and others.
Because of the nature of the service which
will not permit selection of favorable weather
conditions for flaring of gases the flare must
be designed for satisfactory operation in all
weather conditions such as wind, rain, cold,
atmospheric inversion and others.
Complete burning of flared gases can be said
to exist if the flare is equipped with a flame-
retaining tip or discharge nozzle of completely
proven design for any discharge rate; a num-
ber of extremely stable pilots according to the
flare size and minimum calorific value of
the flared gas in the 200-500 btu/cu. ft. range
according to the nature of the combustibles
present.
A single-stable pilot is satisfactory only for
flares up to 2" in size; two pilots are demand-
ed for flares in the 3" and 4" size and three
or more pilots are demanded in flare sizes
from 6" and up.
When the auto-ignition temperature of the
combustible matter in the flared gases is
800°F or less the gas calorific value (Lower
Heating Value) may be as low as 200 btu/cu.
ft. If the auto-ignition temperature of the
combustible matter is 1150°F the minimum
calorific value is 350 btu/cu. ft. (LHV) and
if the auto-ignition temperature is 1300°F
or more the minimum calorific value is
500 btu/cu. ft.
Pilots must provide a minimum of 300, 000
btu/hr each as based on the LHV of the pilot
fuel; must be capable of completely stable
burning in an inert atmosphere; must be
capable of projecting flame to and over the
flare tip in any condition of wind, rain or
temperature; must be capable of reliable and
instantaneous ignition from a point at grade
and remote from the flare base in any
weather condition or wind velocity and must
be proven capable of ignition of 1% of the
design gas flow to the flare.
It is to be seen, therefore, that pilot design
is a most critical element in complete burn-
ing of flared gases and that pilots designed
for other services are far from suitable for
application to the flare as has been repeatedly
proven in flare operation.
Gases burn with speed and completeness
according to the temperature level of the
flame. Heat from the pilots not only initiates
ignition of the flared gases but more impor-
tantly, perhaps, the heat from the pilot
elevates and maintains flame temperature at
levels suitable for complete burning regard-
less of weather conditions. Gases of less
than 200 btu/cu. ft. can be forced to burn
through addition of enough pilots, or heat.
Hydrocarbons and hydrocarbon-derived
organics burn with speed and excellence
according to the weight-ratio of hydrogen to
carbon present in the flared gases.
The flare will at times and according to gases
as flared, produce smoke to a greater or
lesser degree. The smoke may be black
or grey-blue and light according to hydro-
carbons or sulphur compounds as burned
respectively.
When black smoke is produced there is in-
complete burning of hydrocarbons. The black
smoke is carbon from the hydrocarbons.
-------
Flare-Burning of Waste Gasei
Light blue-grey smoke is produced as sul-
phur compounds are burned and is present as
the SOg produced in complete burning reaches
dew-point temperature.
Hydrocarbons as flared burn with excellence
and completeness according to the weight-
ratio of hydrogen to carbon present (H/C
ratio by weight). Methane (H/C = 0. 33) pro-
duces a bright yellow flame with no smoke.
Propane (H/C = 0. 22) makes quite heavy
smoke. Ethane (H/C = 0. 25) also makes a
bright yellow flame but with light trailing
smoke. Thus it can be presumed that
gases having H/C ratios of 0. 28 can be burned
without smoke.
Flares can be designed for smokeless opera-
tion where the H/C ratio by weight is less
than 0. 28 through forced entry of water
vapor to the flame. The water vapor may
be either as steam or from water sprayed
into the flame.
The carbon combines with water vapor
through the water-gas shift reactions (C +
H2O = CO + H2 or C + 2 H2O = CO2 + 2 H2)
to enrich the H/C ratio through production
of rapid burning gases. These reactions are
quite rapid at 1650°F or more.
Black smoke from flare burning of gases,
being carbon in particle size range from
0.01 to 0. 13 microns (Perry), is much
more a nuisance than toxic. However, oxide;
of sulphur, Cl 2 and HC1 are toxic and there
are severe limitations on ground-level
concentrations of them.
Thermal-rise from the flare is based on
1800°F for diffusion of products of flare
timing in the Sutton-Lowery equations for
establishment of flare height. These equa-
tions as well as much air-pollution data arc
to be found in "Air Pollution Handbook"
(McGraw-Hill).
At the present time there is but one source
of definitive information on flare design
because of the great complexity of flare
design functions and because of patent status.
The only group which has the facilities for
research and knowledge of theoretical com-
bustion functions is the John Zink Company,
Tulsa, Oklahoma.
-------
Section 5
STATE OF THE ART AND RESEARCH
Current Research on SOX Control
Formation and Control of Oxides of Nitrogen
in Combustion Processes
-------
CURRENT RESEARCH ON SOx CONTROL
Daniel Bienstock*
I THE PROBLEM OF SULFUR OXIDES
A Concern
The sulfur oxides irritate the respiratory
system of man, cause extensive damage
to plants even at very low concentrations,
and are corrosive to building materials.
It is probably the number one air pollution
problem.
B Magnitude
Approximately 21 million tons of SOo are
emitted each year as the result of the
combustion of coal and fuel oil. If only
50% of this amount could be recovered as
sulfur it could add about 5 million tons
of elemental sulfur to the economy,
worth about $123 million per year. Some
recovery processes involve further oxida-
tion and recovery of the sulfur as sulfuric
acid. This would provide 15 million tons
of sulfuric acid worth approximately
$300 million.
C Sources of Sulfur Dioxide Emission
SO2 pollution can result from the burning
of coal; the combustion of petroleum
products; the refining of petroleum; the
smelting of ores containing sulfur; the
manufacture of sulfuric acid; the burning
of refuse; and the burning or smoldering
of coal refuse banks.
II LIQUID FUELS
A Desulfurization of Fuel Oil
The combustion of petroleum products
accounts for 21% of the SO2 emitted in the
country. Of this about 77% of the total
emission of SOn from petroleum products
results from the combustion of residual
fuel oil.
Hydrogen treating at high pressures in
presence of a catalyst is the most practi-
cal way of accomplishing any significant
degree of sulfur reduction for most
refinery stocks. There are several
commercial processes available: The
H-Oil, Gulf HDS, and the Texfining of
Texaco.
Bechtel recently completed a computer
study of the economics of residual fuel
desulfurization. The cost of lowering the
sulfur content in a California residual
fuel from 1. G to 1% S is 21
-------
Current Research on SOy Control
C Corona
General Electric has treated coal with
hydrogen in a corona discharge to split
off the sulfur. No significant success
reported.
D Extraction
The spencer Chemical Company under
contract by Office of Coal Research has
produced an ash and sulfur-free coal.
The cost, however, of converting the
coal is far too expensive for consideration
as a boiler fuel.
E Bacterial Action
Use of bacteria to attack the pyrite has
been studied. This requires fine grinding
of coal and a water slurry. Method does
not appear promising for processing
large quantities of coal for power boilers.
F Gasification
Gasification and removal of the sulfur as
H2S has been considered but the conclusion
reached that this route is uneconomic.
IV LIQUID SCRUBBING PROCESSES
A Battersea
Since 1935 a gas-washing plant at the
coal-fired Battersea Power Station has
used the water of the Thames River to
which a small quantity of chalk has been
added. More recently the same process
was installed at Bankside Power Station
for scrubbing the flue gas resulting from
burning a high-sulfur fuel oil.
B Howden-I. C. T. Process, Use of Lime in
a Cyclic Non-Regenerative Process
Employs a lime or chalk slurry (5-10%)
circulated through wooden grid-packed
towers. The plant of the Fulham Power
Station, London, worked for several years,
was shutdown during World War II and
not reopened.
C Ammoniacal Solutions
By employing an ammonia solution instead
of lime the sulfur is recovered in a more
useful form principally as ammonium
sulfate, sulfur dioxide, or elemental
sulfur.
In these wet processes the scrubbed gas
is cooled, loses its buoyancy, and
descends in the neighborhood of the stack.
Unless complete removal of SO2 is
effected, a greater local awareness of
the presence of SO2 occurs than before
the gas cleaning. Three hot SO9- removal
processes have been developed to the
experimental stage from which operating
data and cost information are obtainable.
These are the Reinluft, the Catalytic
Oxidation, and the Alkalized Alumina
Processes.
D The Reinluft Process
The absorbent is a fixed slowly moving
bed of an activated char. The SO2 in the
gas is oxidized to SO3 and adsorbed with
H2O on the char to form H2SO4.
E The Catalytic Oxidation Process
The flue gas passes through a fixed bed
of V2O5 where the SO2 is oxidized to SO3.
The product is 70% H2SO4.
F The Alkalized-Alumina Process
The flue gas is fed at 625°F where the
SO2 and SO^ are absorbed by alkalized
alumina spheres, 1/16-inch diameter,
in free fall. Elemental sulfur is the
end product.
A cost estimate was recently made in
treating the effluent of an 800 MW power
plant by these 3 processes.
-------
Current Research on SOX Control
CAPITAL REQUIREMENTS AND NET OPERATING COSTS
Process
Reinluft
Alkalized alumina
Catalytic oxidation
Capital
Requirement
dollars
15,800,000
8,510,000
17,460,000
Net
$/yr.
3, 191,900
2, 205, 800
1,670,200
operating cost
$/ton of coal
1.44
1.00
0.75
-------
FORMATION AND CONTROL OF OXIDES
OF NITROGEN IN COMBUSTION PROCESSES
J. D. Sensenbaugh*
During the early investigation of the Los
Angeles smog problem, the reactions respon-
sible for the smog formation were not under-
stood. In 1952, Haagen-Smit^1) suggested
that a complex series of photochemically-
initiated reactions between hydrocarbons and
oxides of nitrogen might be responsible for
the observed phenomena. Since then, nu-
merous investigators have firmly established
this mechanism for the production of photo-
chemical smog. The hydrocarbons required
for these reactions enter the atmosphere pri-
marily from vehicle exhausts, while the oxides
of nitrogen are produced by combustion pro-
cesses of all kinds.
I CHEMISTRY OF NITROGEN OXIDES
A number of oxides of nitrogen are known.
The most common are nitrous oxide, N2O;
nitric oxide, NO; nitrogen trioxide, N2O3;
nitrogen dioxide, NO2; nitrogen tetroxide,
N2O^; and nitrogen pentoxide, N2OV
Nitrous oxide is reasonably stable at room
temperature, but decomposes readily on
being heated. There is no evidence that N?O
participates in the smog-forming reactions.
Nitric oxide is the most stable oxide of nitro-
gen. It is formed by the reaction of nitrogen
and oxygen at high temperatures. At room
temperature, nitric oxide oxidizes in air to
nitrogen dioxide:
2NO + O_
£• i.
Nitrogen trioxide is a blue liquid below -21°C
(-6°F). When heated to room temperature
and above, N2Og dissociates, giving a mix-
ture of NO and NO2.
NO
NO,.
As mentioned above, nitrogen dio.xide, NO9,
is formed in air by the oxidation of NO. if
exists in equilibrium with its dimer, nitrogen
tetroxide, N?O •
2ND.
This equilibrium is shifted to the right on
cooling and to the left on heating. At normal
ambient temperatures, NO.? predominates.
Nitrogen pentoxide is the anhydride of nitric
acid. At room temperature, it exists as a
white solid. There is no indication that N9Or
occurs in polluted atmospheres to any extent!
if at all.
In summary, the evidence indicates that, of
the oxides of nitrogen discussed, only NO
and its oxidation product, NO9, are of
significance as air pollutants."
II FORMATION OF NO IN COMBUSTION
In ordinary combustion calculations, it is
customary to assume that the nitrogen in the
combustion air supplied to the furnace is inert
and does not participate in the combustion
reactions. From the standpoint of chemical
reactivity, nitrogen is, indeed, a relatively
inert element. However, a mixture of nitrogen
and oxygen, when subjected to a high tem-
perature (in the range of 2800 - 4000°F) such
as provided by a flame, will react to produce
a significant quantity of NO, according to the
reaction:
-2NO
AH = +43. 2 kcal.
The relatively high positive heat formation
shown indicates that a high temperature is
necessary to furnish the heat absorbed in
this reaction.
*Research Department, Combustion Engineering Inc. Prospect Hill Rd. Windsor, Conn.
PA.C.ce. 16. 5.66
-------
Formation and Control of Oxides of Nitrogen
Thermodynamic considerations indicate that,
the higher the temperature, the greater the
amount of NO produced, provided that chem-
ical equilibrium is attained. However, in a"
practical situation, equilibrium conditions
are not reached. In addition to the thermo-
dynamics of the reaction, one must take into
consideration the factor of kinetics, i.e.,
the rate of chemical reactions. As a matter
of fact, the formation of NO by the reaction
of N2 and ©2 is a reversible reaction:
f
2 NO,
with the reaction rate donstant for the forward
(formation) reaction indicated by kf and for
the reverse (decomposition) reaction indicated
by kr. These reaction rate constants for both
the forward and reverse reactions, i.e., both
kf and kr, increase rapidly with temperature.
However, the decomposition rate constant,
kr, is always greater than the formation rate
constant, kf. For example, at 4400°F,
kr = 150 kf, while at 2800°F, kr = 8000 kf.
Thus, as the temperature decreases in passing
through a boiler, the decomposition rate pre-
dominates, leading to lower net NO concen-
trations.
Theoretical curves, based on typical boiler
operating conditions and including both ther-
modynamic and kinetic considerations, are
shown in Figure 1. It is seen that below
2800°F, the net production of NO is very
small. From a practical standpoint, this
means that, as the temperature falls below
2800°F in passing through a boiler system,
the NO formed at higher temperatures is
effectively "frozen" into the gas mixture,
since the system is quenched too rapidly
for the reverse reaction to become effective,
and equilibrium concentrations are never
approached.
The above discussion has been concerned
with the formation of NO. Spectroscopic
studies by Haagen-Smit et al.(2) have indicated
that almost all of the oxides of nitrogen found
in boiler flue gas is present as NO, with only
a minor proportion present as NO-. It has
been previously stated that NO is oxidized in
air to NO2- However, the rate of this
oxidation reaction is strongly dependent on
the NO concentration. The rate is rather slow
at concentrations found in the atmosphere.
For example, at 1 ppm NO, it takes about
100 hours for half the NO to be oxidized to
NO2, and at 0. 1 ppm NO, about 1000 hours
are required for 50% conversion to NO2.
These figures hold in the absence of ozone,
hydrocarbons, sunlight, or other factors that
increase the rate of NO oxidation. In any
case, the principal nitrogen oxide emitted to
the atmosphere in boiler flue gas is NO, and
subsequent oxidation in the atmosphere is
dependent on a number of factors included
in the whole complex of reactions involved
in photochemical smog formation.
Insofar as emissions to the atmosphere from
combustion processes are concerned, the
question of the particular nitrogen oxide
emitted is immaterial. This is because the
usual method of measuring such emissions,
the phenoldisulfonic acid method,^) does
not differentiate between NO and NO2, but
measures the total of these two oxides. Ac-
cordingly, it has become customary to refer
to the total oxides of nitrogen measured by
this method as NOX, a practice that will be
followed in the balance of this paper.
Ill FACTORS AFFECTING NO FORMATION
The concentration of NOX in boiler flue gas
depends on a host of factors involved in boiler
design and operation. Generalizations can
be made regarding the effect of these vari-
ables, but extensive studies^4- $) Of NOX
emissions have shown that the exact level of
emission from a particular unit cannot be
predicted. In this connection, the authors
of one extensive report^5) make the follow-
ing statement:
"The degree and direction of the effect
of operating variables upon NO pro-
duction must be determined individually
for each particular unit to be considered.
It was found that actual rates of NOX
emission from sister units may he dif-
ferent for operating conditions which
are the same for each unit within the
limits of ability to determine. "
-------
Formation ai.d Control_of_Qxides of Nitrogen
THEORETICAL CURVES OF NO CONCENTRATION VS
TEMPERATURE FOR OIL AND GAS FIRING
1000
800
600
o.
0.
400
200
0
2800
3000 3200
TEMPERATURE (°F)
Figure 1
3400
-------
Formation and Control of Oxides of Nitrogen
IV EFFECT OF FUEL AND TYPE OF FIRING
Two of the major factors affecting NO pro-
duction are the fuel used and the method of
firing. These will be discussed together.
Most of the work on oxides of nitrogen pro-
duction has been done with oil and gas fuels.
The general ranges for these fuels with
horizontal and tangential firing are as follows:
Fuel
Oil
Oil
Gas
Gas
Firing
Horizontal
Tangential
Horizontal
Tangential
ppm NO
— x
500 - 700
200 - 400
300 - 500
100 - 200
Data from a number of plants are shown in
Table 1 and Figure 2. The average NO con-
centration found in these tests for horizontally-
fired, oil-burning units is 560 ppm. compared
with an average of 293 ppm for tangential firing
of oil. In other words, the average concentra-
tion obtained with tangential firing is 52% of
that found with horizontal firing. With gas fuel,
the average concentration found for horizontal
firing is 339 ppm, while that for tangential
firing is 160 ppm. In this case, the average
concentration for tangential firing is 47% of
that for horizontal firing.
Little work has been done on NOX emissions
from coal-fired units. Results of tests on
four units with different types of firing have
been published. (6, 7, 8) oata obtained at full
load are shown in Table 2. It should be noted
Table 1. COMPARISON OF TYPE OF FIRING AND FUEL
NORMAL FULL LOAD OPERATION
Plant
El Segundo (11)
A
B
C
E
F
G
El Segundo (11)
A
B
D
E
F
Fuel
Oil
Oil
Oil
Oil
Oil
Oil
Oil
Gas
Gas
Gas
Gas
Gas
Gas
Firing
Horizontal
Horizontal
Horizontal
Horizontal
Tangential
Tangential
Tangential
Horizontal
Horizontal
Horizontal
Horizontal
Tangential
Taneential
Ave. ppm N0.c
685
567
SOS
482
362
309
209
520
290
319
226
164
157
-------
Formation ar.d Control of Oxides of Nitrogen
COMPARISON OF HORIZONTAL AND TANGENTIAL FIRING, OIL
AND GAS FUEL, NORMAL FULL LOAD OPERATION
700
0
PLANT
FIRING
FUEL
*EL SEGUNDO, REFERENCE II
F G ELS" A B D E F
h«—HORIZ.-H K-TANG.-H f-e-HORiz.—H KTANGJ
OIL H N GAS H
Figure 2
-------
Formation and Control of Oxides of Nitrogen
Unit
A
B
C
D
Table 2. NOV from Coal-Fired Units. Full_Loa_d_ Operation
Samples Taken Before Dust Collector ~
(Data Taken from Reference 8)
Type of Boiler
Average ppm NOX
^Corrected to Constant CC>2
Downward-fired, dry bottom
Front-fired, dry bottom
Tangentially-fired, dry boiiom
Horizontal opposed, wet bottom
267
595
500
520
that only one unit of each type was included
in these studies, so the results are not
necessarily representative of the emissions
to be expected from a particular type of firing.
V EFFECT OF EXCESS AIR
Since NO is formed by the high temperature
reaction of nitrogen and oxygen, one would
expect that the amount of excess air available
would affect NO production. Data obtained
at several plants for oil and gas fuels are
shown in Figures 3 and 4. It will be seen
that, at the O2 levels present in conventional
operation, a decrease in excess air produced
a decrease in NOX. The effect is particularly
pronounced for horizontal firing.
In recent years, there has been a trend toward
operation of oil-fired units at low excess air
levels of 2 - 5% (0. 4 - 1%O2) instead of the
conventional 10 - 20% (2 - 4%O2). This has
been done to avoid problems associated with
the formation of SO3. However, low excess
air operation is also beneficial from the
standpoint of reducing NO . Figure 5 shows
test data from three plants. These units
are similar in size and are all tangentially
fired. In this case, the results from three
units fall nicely on the same curve.
VI EFFECT OF GAS RECIRCULATION
Many units employ the recirculation of a por-
tion of the flue gas into the furnace as a
means of steam temperature control. Intro-
duction into the furnace of gas containing less
oxygen than the combustion air would be
expected to affect the formation of NO. Also,
depending on the point of introduction, the
recirculated gas may act to lower the flame
temperature.
Test results from two different plants are
shown in Figures 6 and 7. In both cases,
the NOX concentration decreases with in-
creasing gas recirculation, although in the
case of the tangentially-fired unit shown in
Figure 6 the reduction was relatively small.
In going from zero to 15% gas recirculation,
the NOX concentration was reduced about 15%
from its initially rather low value.
There is so much variation from one unit to
another in the quantity of gas recirculation
needed for steam temperature control and in
the point at which the recirculated gas is in-
troduced that the effect of gas recirculation
is difficult to predict.
VII EFFECT OF UNIT SIZE
It would be useful to be able to predict theNOx
emission from a given unit on the basis of data
on other units using the same type of fuel and
firing method. An attempt was made to cor-
relate NOX data from a laboratory package
boiler burning oil with data obtained in the
field on horizontally-fired oil-burning with
data obtained in the field on horizontally-fired
oil-burning units. Although some similarities
in trends were found, no useful correlation
curves could be developed. This was attribut-
ed to the fact that the single burner in the
package boiler "sees" only cool surface.
-------
__Formation_a.id_Coritrol of Oxides^ ofNitrogen
EFFECT OF EXCESS AIR, OIL FUEL
700
600
500
400
a. 300
200
100
PLANT C
HORIZONTAL FIRING
PLANT G
TANGENTIAL FIRING
PERCENT 02
Figure 3
-------
Formation and Control of Oxides of Nitrogen
x
O
2
Q.
Q.
700
600
500
400
300
200
100
EFFECT OF EXCESS AIR, GAS FUEL
HORIZONTAL
HORIZONTAL
TANGENTIAL
PERCENT 02
Figure 4
-------
_Formatign and Contrpl_of;_Oxides_nfJMitrogen
EFFECT OF LOW EXCESS AIR, OIL FUEL
320
280
240
200
Q.
£L
• PLANT G
• PLANT H
A PLANT I
Figure 5
-------
Formation and Control of Oxides of Nitrogen
EFFECT OF GAS RECIRCULATION, OIL FUEL
700
x
O
2
0.
Q.
200
100
PLANT G
TANGENTIAL FIRING
10
20
PERCENT GAS RECIRCULATION
Figure 6
10
-------
Formation and Controj^o^Qxides of Nitrogen
700
600
500|-
X
O
a.
a.
400
300|
2001
100!
EFFECT OF GAS RECIRCULATION.OIL FUEL,
HORIZONTAL FIRING (REFERENCE 5) '
8
40 60 80
100
GAS RECIRCULATION - PERCENT DAMPER OPEN
Figure 7
11
-------
Formation and Control of Oxides of Nitrogen
while interaction occurs between the flames
in a multiple burner installation.
Similar results were reported^5) in tests on
large units where the number and spacing of
burners in use were varied. It was found
that, when the burners in operation were
closely grouped or when more burners were
in use, more NOX was produced than when the
same amount of fuel was burned using fewer
burners with wider spacing. Again, the re-
sults were attributed to the relative amount
of cold waterwall each burner sees; when
more cooling surface is available to absorb
radiant heat from each individual flame, less
NO is formed.
A correlation has been published between NOX
emission and gross heat input to a unitJ9- 10)
This correlation takes the form of log-log
plots covering some six or seven decades.
The authors of one of these reports^9) give
the following precaution regarding the use
of the plots:
"The graph should not be used to esti-
mate NOX emissions from any given
unit, because individual units are sub-
ject to so many operating variables as
well as individual combustion para-
meters that actual emissions of NOX
from any single unit at a given time may
vary widely from the average for the group. "
This precaution is very important. For ex-
ample, the curves would predict a concen-
tration of 700 ppm NOX for burning oil at
full load in a particular tangentially-fired
boiler. The average measured value under
these conditions was 209 ppm. Part of this
discrepancy may be due to the fact that
tangentially-fired utility boilers were not
included in the test data on which the cor-
relation is based, 'so that, at the high heat
input end, the curve is weighted in favor of
the higher emission rates typically shown
by horizontally-fired boilers. In any case,
the correlation must be used with full recogni-
tion of the fact that it will give only a rough
idea of the emission from a particular unit.
VIII POSSIBLE CONTROL METHODS
The preceding discussion of factors affecting
NO formation suggests that NOX emissions
could be reduced in the following ways:
a Change of fuel
b Minimize NO formation by
X
1 Lower excess air
2 Lower flame temperature
If it is not possible to obtain sufficient
reduction by means of the approaches
indicated above, NOX might be removed
from flue gas after formation by means
of the following:
c Absorption
d Adsorption
e Catalytic decomposition
A Change of Fuel
There is no doubt that the substitution of
gas for oil would result in lower NO ,
emission. However, this is not always a
practical course to follow. In many areas,
considerations of fuel supplies and econo-
mics make another course more desirable.
B Minimize NOX Formation
The present trend toward low excess air
firing of oil is well established and is ex-
pected to continue. As indicated pre-
viously, the excess air levels in question
are effective in reducing NO emissions.
X
The strong temperature dependence of the
NO formation reaction indicates that any
measure resulting in lower flame tem-
perature would lead to lower NO concen-
trations. One approach is to use the
tangential firing concept, which uses the
furnace itself as the burner and inherently
produces lower maximum flame temperatures.
12
-------
_ForniatigtT_a!K[ Control of C)xides of Nitrogen
If horizontal firing is preferred, NOX
formation can be greatly reduced by the use
of two-stage combustion, as described by
Barnhart and Diehl.*11) In this system,
90 - 95% of the theoretical air is intro-
duced through the burners with the remain-
ing 15 - 20% required for combustion en-
tering through auxiliary air ports above
the burners. Their results at El Segundo
using 95% of theoretical air through the
burners are shown in Figure 8. It may
be seen that a 44% reduction in NOX con-
centration was obtained with two-stage
combustion compared with normal operation.
Figure 8 also shows the results of tests
in which two-stage operation was simulated
at two plants. These tests were conducted
by operating at reduced load with the top
row of burners off and the dampers closed
in order to get a reference value. This
was followed by the introduction of auxiliary
air through the idle top burners. Again,
approximately 95% of theoretical air was
introduced through the burners. At plant
B. with horizontal firing, a 45% reduction
in NOx was found with two-stage combustion
compared with normal operation. At plant
G, with tangential firing, the reduction in
NOX with two-stage combustion was only
22%; however, as usual with tangential
firing, the NOX level for normal operation
was much lower.
C Absorption and Adsorption
If NO has to be removed from flue gas
after "formation, absorption or adsorption
processes might be considered. Peters^12)
and Peters and Holman^13) have studied
the absorption of NO2 in water and aqueous
NaOH solutions using a variety of absorption
tower packings. They found that extremely
large quantities of water would be required
to absorb NO2 appreciably from gases con-
taining less than 2000 ppm NCL. Also, at
temperatures below 100°F, there was no
significant difference in NO2 absorption
by water and by 20% NaOH. Since NO is
only slightly soluble in water, it would be
expected to be absorbed only slightly by
water or basic solutions.
Littman, et al. have studied the ad-
sorption of NOX on activated charcoal. It
was found that NO7 was adsorbed, but NO
was not. Foster and Daniel.s(J5) studied
a process in which gas containing NO was
dried and passed over silica gri. The
silica gel acted as a catalyst for the oxi-
dation of the NO to NO,, and the latter
was adsorbed on the silica gel. At room
temperature and with agas stream containing
1.0- 1.5% NO, adsorption efficiencies as high
as 99% were obtained. However, when the NO9
content was reduced to 2000 ppm (still 3- 10
times the NOX concentration commonly found
in boiler flue gas), the efficiency of NO? removal
dropped to about 50%.
Even if an efficient adsorption process
were developed, the adsorbent would
have to be recovered for recycling. This
would involve desorbing the NO, by heat-
ing, with subsequent collection "of the
NO2, perhaps by absorption.
Both absorption and adsorption methods
have inherent disadvantages. To achieve
effective collection, both methods must
be carried out at relatively low tempera-
tures. Final disposal of the collected ma-
terial must also be provided. The studies
cited indicate that large amounts of absorp-
tion or adsorption media would be required,
leading to large equipment size and high
costs.
D Catalytic Decomposition
Another approach to the removal of NO
from flue gas might be catalytic decom-
position to nitrogen and oxygen. In general,
this appears to be more suited to small
volume applications such as automotive
exhaust, since the cost would probably be
excessive for treating boiler flue gas.
Catalytic systems have been described^16)
for promoting the reaction between NOX
and hydrocarbons to yield carbon dioxide,
water, and nitrogen. Such systems have
been applied to nitric acid plant tail gas
containing of the order of 5000 ppm NOX.
However, as usual in such situations, the
problems are much more severe when
dealing with much more dilute boiler flue
gas.
13
-------
Formation and Control of Oxides of Nitrogen
TWO STAGE COMBUSTION, OIL FUEL
700
600
500
400
Q. 300
Q.
200
I 00
0
PLANT
FIRING
)
1
—
OPERATION
NORMAL KSS53
2-STAGE 1 1
I
i
I
s
§§|
I
N^
1
1
1
I
1
I
—
ELS*
HORIZONTAL
B G
HORIZONTAL TANGENTIAL
*EL SEGUNDO, REFERENCE II
Figure 8
-------
Formation and Control of
The reduction of NOx by carbon monoxide
or carbon monoxide and hydrogen in the
presence of various copper-containing
catalysts has been described.*1'' IB| *9^
Such systems appear to be technically
feasible for application to motor vehicle
exhaust gas, but the necessary hardware
has not be developed. However, in view
of the recent action by the California State
Board of Health in setting a 350 pprn
standard for NOX in auto exhaust, <20' the
required exhaust treatment devices will
be developed in time. As a matter of
interest, almost six years elapsed between
the adoption of exhaust standards for car-
bon monoxide and hydrocarbons and the
installation of approved devices on
automobiles.
DC SUMMARY
Of the various oxides of nitrogen, only NO
and NO2 participate in the reactions involved
in the formation of photochemical smog. The
NO originates in high temperature combustion
processes, while NO2 is formed by the oxi-
dation of NO.
The concentration of NOX in boiler flue gas
depends on so many interrelated factors that
the concentration to be expected from a parti-
cular unit cannot be predicted without mea-
surement. However, certain generalizations
can be made. The production of NO will
vary with the fuel and type of firing.X Oil pro-
duces greater NO^ concentrations than gas.
and horizontal firing gives higher concentra-
tions than tangential firing. In general, a re-
duction in excess air produces lower NOX
levels. This is particularly noticeable at
the low excess air levels now in use with oil
firing.
Possibilities for reducing the quantity of NO
formed include 1) change of fuel, 2) low ex- X
cess air operation, and 3) reducing flame
temperatures. A change in fuel used is
not always economically attractive, so other
ways should be considered. Low excess air
operation with oil firing is practical and
effective; it is expected that this approach
will be increasingly employed in the future.
Lower flame temperatures with resulting
lower NOx formation may be realized by use
of tangential firing or by two-stage com-
bustion with horizontal firing.
Removal of NOx from boiler flue gas by ab-
sorption, adsorption, or catalytic decomposi-
tion methods does not appear to be practical
However, the use of catalytic decomposition
does appear feasible for automotive exhaust
and it will probably be used in this application.
REFERENCES
1 Haagen-Smit, A. J. Ind. Eng. Chem.
44:1342. 1952.
2 Haagen-Smit. A. J., Taylor. V. D., and
Brunelle, M. F. Int. J. Air Poll
2:159. 1959.
3 ASTM Standard No. D-1608.
4 Sensenbaugh, J. D., and Jonakin, J.
ASME Paper No. 60-WA-334.
5 Report No. 3 of Joint Project on Emissions
of Oxides of Nitrogen from Stationary
Sources in Los Angeles County. 1961.
6 Cuffe, S. T., Gerstle, R. W., Orning,
A. A. and Schwartz, C. H. J. Air Poll.
Control Assn., 14:353. 1964.
7 Gerstle, R. W., Cuffe, S.T., Orning, A. A.
and Schwartz, C. H. Ibid. 15:59. 1965.'
8 Orning, A. A., Scwartz. C. H. , and Smith,
J. F. ASME Paper No. 64-WA/FU-2.
9 Report No. 4 of Joint Project on Emissions
Of Oxides of Nitrogen from Stationary
Sources in Los Angeles County. 1961.
15
-------
Formation and Control of Oxides of Nitrogen
10 Woolrich, P. F. Amer. Indus. Hyg. Assn.
Journal. 22:481. 1961.
11 Barnhart, D. H., and Diehl, E. K. J. Air
Poll. Control Assn. 10:397. 1960.
12 Peters, M.S. Chem. Eng. 62:197. 1955.
13 Peters, M.S., and Holman, J. C. Ind.Eng.
Chem. 47:2536. 1955.
14 Littman, F. E., Ford, H. W., and Endow,
N. Ibid. 48:1492. 1956.
15 Foster, E.G., and Daniels, F. Ibid. 48:
986. 1951.
16 Donahue, J. L. J. Air Poll. Control Assn.
8:209. 1958.
17 Sourirajan, S. and Blumenthal, J. L. Int.
J. Air and Water Poll. 5:24. 1961.
18 Baker, R.A., Doerr, R. C. J. Air Poll.
Control Assn. 14: 409. 1964.
19 Baker, R.A., and Doerr, R. C. Ind. Eng.
Chem. Proc. Des. and Devel. 4:188.
1965.
20 Clean Air Quarterly. 9:4, 1. 1965.
16
-------
Section 6
PERMIT SYSTEM
Permit System - Combustion Evaluation
-------
PERMIT SYSTEMS - COMBUSTION EVALUATION
Herbert C. Johnson*
I INTRODUCTION
Installation permits must be obtained for fuel
burning equipment in most cities and many
counties of most states. Permits usually are
issued by building departments, fire depart-
ments, health departments, or air pollution
control agencies. Central permit bureaus
are being established, or some other coor-
dinating system developed in some cities to
expedite issuance of permits.
Well administered permit systems have con-
tributed to health and safety, to more efficient
use of fuels, and to reduced maintenance
costs.
A Information Required to Obtain a Permit
1 Location of installation, address, firm
name.
2 Plot plan showing equipment location on
property, type and height of adjacent
buildings.
3 Plan of room or location of equipment
should be to scale showing clearances,
air supply, fuel supply, breeching, and
stack. For incinerators, show storage
for refuse and space for charging and
ash cleaning. Show fire doors, fire
protection, fire walls, etc.
4 Supply manufacturer's drawings and
specifications, including materials of
construction, type and size of burners,
combustion volume, size of air ports,
and draft required.
5 Capacity requirements
a Btu's required for heat or processing
average, maximum, minimum, etc.
b Incinerators, Ib/day to be burned,
type of refuse.
6 Piping and wiring diagrams, and flame
safety devices may be required to
assure meeting codes.
7 Process flow sheet - not usually re-
quired for small equipment, may be
necessary where industrial processes
are involved.
8 Proposed stack height. For large
equipment burning sulfur containing
fuels or discharging other air con-
taminants, calculations showing ade-
quacy of dispersion by stack may be
required.
9 Air pollution control devices. Addi-
tional control equipment may be
required to removp fly ash or other
forms of air pollution. Manufacturer's
guarantees should be included.
B Obtaining an Operating Permit
Assuming that installation has been
obtained and equipment installed.
1 Notify inspection agency of completion,
request inspection.
2 Correct any discrepancies in installa-
tion found by inspector.
3 Demonstrate operation for inspector.
Make adjustments as required by
inspector.
4 Perform stack tests or other tests
required to determine compliance.
5 Modify equipment or install additional
control equipment as necessary to
comply with regulations.
E"gi"eer' Ba? Area Air Poll"tion Control District. San Fr
ancisco,
PA.C. ce. 22. 7. 6G
-------
Permit System - Combustion Evaluation
C Retaining on Operating Permit
The intent of a permit system implies
continued surveillance and testing if
necessary. To continue meeting all
requirements.
1 Inspection and preventive maintenance
to assure proper operation.
2 Type of fuel or refuse must conform to
permit application.
3 Operators should be properly instructed
and supervised.
4 Load on equipment should not be allowed
to exceed designed capacity.
A permit system will be successful
only if adequate information is included
in the application, the reviewing
engineer is qualified in the field of
fuel burning equipment and combustion,
and the installing contractor completes
the installation according to plans and
specifications. Adjustment and testing
is necessary before the installation is
turned over to the operators. Proper
training and supervision of the operating
personnel, plus maintenance and in-
spection, are requisites to successful
continued operation.
Incinerators require careful operation,
periodic cleaning, and maintenance.
Continued firm supervision is usually
necessary to prevent development of
improper operating procedures.
-------
Section 7
POLLUTANT CALCULATIONS
AND CORRECTIONS
Expression of Pollutant Concentration and Emission
-------
'.'UiMTHATION ANO EMISSION
I EXPKKSS1ON OK PAUTICULATi;
POLLUTANT CONCENTRATION AND
EMISSION
A Paniculate Pollutant ; 'u;icenlration
i General expressions
a Pounds per thousand pounds
(#/1000/0
A particulnte pollutant concentra-
tion may be expressed as pounds
of pollutant per one thousand
pounds of gas-mixture according
to the following definition:
(pounds of particulate pollutajrt[
(pounds of gas-mixture)
(J)
Weigh*, per cubic foot
!\ paniculate pollutant concentra-
tion may be expressed as a weight.
of pollutant per cubic- foot of gas-
mixture according to the following
definition (the weight units com-
monly used are pounds or grains):
(Weight/ft1* at a specified T and P)
(Weight of partieulate pollutant)
(Cubic feel of a gas-mixture at a
specified T and P)
2 Kxpressions for effluents from
eoal combustion
The weight of dry effluent gas per unit
weight of coal is given by:^y
|_11 CO., + U 0., + 7 (fO + N2)]
~~ TtTo., + ~CO).
where proportion by volume (not %) is
substituted for the appropriate chemical
symbols.
With no excess air and complete com-
bustion, eoal, when burned, theoretical-
ly yields 18. 5'!',, CO2, 0.0% O0, and 81.5%
N.}. When 50To excess air is~used and
there is complete combuslic i, experi-
ment shows an effluent of 12.25% CO. ,
fi.75%0.,, ancl81%N.,. The latter2'
data when substitutedln equation (.'5)
provides 20. C>, the constant appearing
in the following equations.
liquations (4) through (7) that follow,
are related to effluents from eoal
furnaces only:
(Weight /ft
at a specified
T and P ;ind 12% CO
(Weight of particulate pollutant) (J 2)
Cubic feet of a gas-mixture at al
specified T and P |
r% of CO2 by'
(volume on a I
[ wet basis*
(4)
(Weight/ft3 at
a specified T and
P and 50% excess air)
= M
s(di-,y)
= (Weight of particulate pollutant) V (:i) abov
TCubic feet of a gas-mixture
^specified T and P
at a
Weight of dryeffluenH
gas per unit weight of(
coal. See equation
(20.6)
(
)
(5)
PA.C.ee. 10. 1. ti(i 1
-------
referred
to 12% C02) .
= (10) (pounds of particulate pollutant) (12)
(pounds of gas-mixture)
(%
j 01
of.CO, by voluim.-/
on a wef basis* i
(0)
( #/1000# re-
ferred to 50%
excess air)
= (10) (pounds of particulate pollutant)
Weight of dry effluent
gas per unit weight
of coal. See equation
. (3) above.
(pounds of gas-mixture) " (20.6)
(7)
B Particulate Pollutant Emission
1 Mass rate
A mass rate of emission of a particulate
pollutant is expressed according to the
following definition. Units are commonly
grams per second (gm/sec).
' (Mass of particulate
ppm=:
pollutant emitted)
Mass Kate - -E -
(8)
2 Weight rate
(10) (volume .of gaseous pollutant at a-given
\ T and P.) ,. '
(Volume of a gas-mixture at the same T and
P to which the gaseous pollutant is referred
in the numerator) . ...
b Parts per hundred million (pphm)
A gaseous pollutant concentration is
expressed as parts per hundred
million according to the following
definition:
A weight rate of emission of a particulate
pollutant is exprossod according to the pphm
following definition. Units are com-
monly pounds per hour (tt/hr).
Weight Rate =
(Weight of particulate
emitted)
(Time)
(0)
II EXPRESSION OF GASEOUS POLLUTANT
CONCEN TRA TION A NT) EMISSION
A Gaseous Pollutant Concentration
1 Parts by volume
a Parts per million (ppm)
A gaseous pollutant concentration is
expressed as parts per million by
volume according t.o equation (10)
that follows;.
Q
(10) (volume of gaseous pollutant at a given
. T andP)
(Volume of a gasrmixture at the same T
and P to which the gaseous pollutant is
referred in the numerator)
(11)
c Parts per billion (ppb)
A gaseous pollutant concent ration, is
expressed as parts per billion ac-
cording to the following definition:
(10)
PPb
•'Same as page M asterisk
(volume of gaseous pollutant at a
given T and P) ':
(Vplume of a gas-mixture at the same T
v and P to which the gaseous pollutant is
referred in the numerator) . .
2 Percent by volume.(%)
A gaseous pollutant concentration is
expressed as percent by volume accord-
ing to the following definition. Such an
expression is equivalent to parts per
hundred by volume.
-------
( 10) "(volume of gaseous pollutant at a
given T and P)
(Volume of a gas-mixture at. the same T
and P to which the gaseous pollutant is
referred in the numerator) .
(13)
3 Pounds per thousand pounds (#/1000J)
A gaseous pollutant concentration may
be expressed as pounds of pollutant per
oriathousand pounds of gas-mixture
adcSrding to the following definition:
iannnna\ - (10)3(pounds of gaseous pollutant)
(# / uiuiw - (pounds of a gas-mixture)
4 Grains per cubic foot (gr/ft )
(14)
A gaseous pollutant concentration may
be expressed as grains of pollutant per
cubic foot of gas-mixture according to
the following definition:
_3 _ (Grains of gaseous pollutant)
' " (Cubic feet of a gas-mixture at a
specified T and P)
(15)
5 Micrograms per cubic meter
(jig/M3)
A gaseous pollutant concentration may
be expressed as micrograms- of pollutant
per cubic meter of gas-mixture accord-
ing to the following definition:
, (Micrograms of gaseous pollutant)
(Cubic meters of a gas-mixture at
a specified T and P)
(16)
B Gaseous Pollutant Emission
1 Mass rate
A mass rate of emission of a gaseous
. pollutant is expressed according to the
following definition. Units are com-
monly grams per second (gm/ser)
_ . (Mass of gaseous pollutant .emitted )
Mass Rate - r_.—T—^-.—-.—'• •—••—
(Time) ,
(17)
2 Weight rate
A weight rate of emission of a gas'eous
pollutant is expressed according to the
following definition.'. Units are com-
monly pounds per hour (tf/hr).
Weight Rate
(Weight of gaseous pollutant emitted)
(Time)
(18)
3 Volume rate
Volume _
.Rate
Volume rate of emission of a gaseous
pollutant is expressed according to the
following definition. '
(Volume of gaseous pollutant at a
specified T and P) .
(Time)
(19)
-------
REFERENCES
1 Mark, L.S. Mechanical Engineers'
Handbook, McGraw-Hill Book Co.,
Inc. New York. 195 J.
- Smithsonian Meteorological Tables, Sixth
Edition, Washington, D. C. 1951.
:i Tables of Thermal Properties of Cases,
Circular 564. National Bureau of
Standards. 1955.
4 Vennard, J. K. Elementary Fluid
Mechanics. John Wiley and Sons, Inc.
New York. J947.
5 Perry, J. H. Chemical Engineers' Hand-
book, McGraw-Hill Book Co., IncT ~
New York. 1960.
6 Jacobs, M.B. The Chemical Analysis
of Air Pollutants, Interscience
Publishers. New York. 1960.
-------
Section 8
AIR POLLUTANT EMISSIONS
FROM COMBUSTION
Air Pollutant Emissions from Selected Heat
General and Incineration Sources
-------
AIR POLLUTANT EMISSIONS FROM SELECTED HEAT
GENERATION AND INCINERATION SOURCES
Darryl J. von Lehmden*
I INTRODUCTION
Emission rates for various types of air pol-
lutants from heat generation and incineration
sources have been published in the literature.
The results from one such study' " are sum-
marized in the Tables 1 through 7. Although
the results are unique to the combustion
sources tested, they do permit relative com-
parisons of emission rates from the burning
of various fuels (i. e., coal vs. fueloilvs.
natural gas). The results also permit relative
comparisons of air pollutant emission rates
based on the combustion source size (i.e.,
commercial vs. municipal incinerators;
domestic home heating vs. industrial process
heating).
The emissions measured in the study and
shown in the Tables include: polynuclear
hydrocarbons, carbon monoxide, carbon
dioxide, formaldehyde, gross hydrocarbons,
sulfur oxides, nitrogen oxides and total
particulates.
II SUMMARY OF RESULTS
The results from the heat generation sources
tested are summarized in Tables 1, 2 and 3.
The results from the incineration and open-
burning sources tested are summarized in
Tables 4, 5, 6 and 7.
REFERENCE
1 Hangebrauck, P.R., von Lehmden, D. J.,
and Meeker, J. E. Hydrocarbon and
Other Pollutants from Heat Generation
and Incinerator Processes. JAPCA,
Vol. 14, No. 7, pp 267-278. July 1964.
*Chemical Engineer, Air Pollution Training,
Training Program, SEC
PA.C.ce.8. 1. 66
-------
Table 1. DESIGN AND OPERATIONAL SUMMARY - HEAT GENERATION SOURCES
Source Fuel
No. Used
1 Coal
2
3
4
5
e
7
8
9 Oil
10
11
12
13
14
15 Gas
1C
17
18
19
Firing Method
Pulverized (dry
bottom
furnaces)
Chain grate
stoker
Spreader stoker
(with ranjec-
tor)
Underfeed
stokera
Band-stoked
Steam-atomized
Low-pressure
air-atomized
Centrifugal-
atomiied
Vaporized
Premix burners
Rated Capacity
per hr
10> Lb Million
Type of Unit Utilisation Steam Btu'
Water-tube
boiler
Water-tube
boiler
Fire- tube
boiler
CasUiron sec-
tional boiler
Hot-air
furnace
Water-tube
boiler
Scotch-iiiarine
boiler
Cast-iron sec-
tional boiler
Hot-air furnace
Hot-air
furnace
Fire-tube
boiler
.Scotch-marine
boiler
Doubln-shell
boiler
Hot nir furnoro
Wall ep.-ire heater
Electric 1080
generation
Process 200
heating
Electric 125
generation
Process 70.fi
heating
Process
hpfltitig
School
heating
Home
heating
Home
heating
Process 22
heating
30
Hospital
heating
Home
heating
Home
heating
Process
heating
Hospital
heating
Home .
heating
v
7.2
3.8
0.28
0.20
23
30
4.2
0.25
0.14
0.0!)
7.2
•1.2
0.18
0.21
0.025
Dust
Collector
Mechanical
electrical
Multiple
cyclone
None
Multiple
cyclone
None
None
None
as-received basis
Vola-
tile, Aeli, S,
% % %
31 20.2 2.3
36 4.3 0.0
44 7.0 3.8
37 4.7 0.8
36 4.7 0.7
19 5 0.8
38 3.9 1.0
38 2.7 0.5
No. 2 Fuel Oil 3.2
(28.5° API)
No. 0 Fuel Oil 0.7
(13. 5° API)
.No. 1 Fuel Oil
(43.5° API)
No. 2 Fuel Oil
(31 .5° API)
No. 2 Fuel Oil
(31.5° API)
' No. I Fuel Oil 0.05
(43° API)
Natural gaa (94. 2%
methane 3.6%
ethane)
Fuel Rate
Lbs
132.000
9,420
12,400
4,290
317
214
4.8
8
1,110
769
35
s.s :
4.4
12
402
42
7.0
7,4
0.52
Operating Conditions D
Gross Btu Steam
Input Rate
— Per Hr *
Million Btu 10' Lb
1560 1120
130 108
147 111
59.2 49
4.4
30
.0.066
0 115
21 17.9
14.4 10.3
0.70
0.17
0.085
0.025
».:s
0.98
0.1S.
0.17
0.012
>uring Test .
Steam Smoke,
Pressure Opacity,
Prig. %
2000
307
450
160
110
37
e
250
125
95
108
!«
30-40
60
20-40
0-20
20-40
0-20
0-20
40-80
5
5
0
0
0
0
0
0-20
0
0
0
• (jrosa heat input.
-------
Table 2. POLLUTANT EMISSION SUMMARY - HEAT GENERATION SOURCES
Flue Ciaa Condition* in Slack
Source Fuel
No. Uaed
1 Coal
2
3
4
5
ft
7
8
9 oil
10
1 1
12
13
14
15 Gu
ie
17
18
10
• Blink, in the
b Pound, of pa.
• API iravilie*
Firin. Flow.
Method eefm
Pulvrritrd 415.000
32.300
CKain irate 4.1. OOO
•tukct
Spreader 18.100
itoter
UndfrOed 3.340
llokrri 3.260
13
Hand- 78
aloked
Sleam- ;, . 200
atuinizert
10. OOO
Low- 195
prewure
air-
atomised
Centrifugal- 145
atom j ted
US
Vaporiied 49
Prtmit 3.640
burnere
325
92
82
11
table indicate that no t*
Temp. iftO.
•F %
260 .'. 4
23', 8 2
430 fl 7
40'i (1 t>
380 2 1
23'.-, 2 1
345 2.2
220 2 1
530 8.5
340 5.4
S30 7 t
170 30
I7t> 2.8
185 1 U
380 3 4
3IO 11.4
170 4 8
140 4 1
295 44
.t wu made-
rtieulate p«r 1000 pounds of dry flue Baa
of the fuel oils ace Klven in Table 1: the
'-Dry B
CO,
12 3
12 3
12 1
10.6
:< 0
2-.'.
2 «
'26
9.0
88
2.9
1 8
1 2
3 6
r, u
•J 4
•i 2
2 0
«!l— •
O, 1000
% Lb»
SO 0 50
6 1 1.90
7 7 0 96
8.5 0.68
17 2 06.1
IS 1 0 21
17 1 0.52
17 7 1 80
8.2 0.32
» 0 0.049
18 'J 0 041
18 3 0 070
10.3 0.067
14 3 0.026
10 0 0.030
lit V 0 010
17 3 0 .011
IT. 5 0 027
-Total Par
Lh Per
.Million
Btu
0 59
2 23
1 31
0 82
0 «2
0 !.1
U 44
1 29
0 306
0 297
0 Oil
0.046
0.080
0 071
0-021
0 032
n ooa
0 007
0 026
adjusted to 50% eireM air.
dtniity of n&tural ga. - 0.0443 Ib per
Table 3. POLYNUCLEAR
Source Kuel
No. Used
1 Goal
2
3
4
5
U
"j
&
'J Oil
10
11
12
13
14
15 C:HK
16
17
18
Firing Method
Pulverized
Chain Rrat« aloker
Spreader stuker
Underfeed stokers
Hund-stuked
SteQin-alornized
I^iw-presaurc air-
ntoinizetl
Centrifvigat-
atnmized
Vnpori/ed
Prcniix liurncrs
lie V]
p£m per
1000 MS*
42
75
71
4!)
7, '.KM
Gl
3,400
340, (XX)
<38
40
1 , 'J(X)
<20
<27
<34
<2'J
:>M
<23
<3i>
ilo(a.)pvrer:
*igm per
Lb Fuel
0.22
0.43
0.44
0.35
140
I.G
ii2
'",
B|-
"Su-
Tcn hie
of Or-
fue)' K&oica
14 ft 07
61 fi 03
3 1 U 03
22. fl 14
170 11
70 3 fl
1'J 12
37 17
11.7 1.0
10 0 27
2.0 «0
1 8 .3IJ
31 94
28 II
10 11
1 . .'• 80
o :i 3:1
0 3 23
1.2 Ifl
i-u U (HOT. 1 if
Oiida of
Carbon Hydroearbou Nitroxen — Oiidea of Sulfur — •
Monoiids (aa Methane) (u NO,) (aa SO,) Kormajdebj-de .
Lb Per l.b Per l.b Per —Lb Per-^ . Lb Per
Million
Rtu
0 004
0 10
0 51
l
a la
0 14
1 1
3 5
<0.1
0 O.V,
0.038
0 075
0 25
0.013
3 00
0 02
O 026
0.030
L»).
HYDROCARBON EMISSION
ie*
19
32
37
26
10,000
120
3.800
KXI.OOO
<2()
47
'.KM)
<4U
,400
101), OOO
•I'M)
IS
Ton
of Million
fuel' Blu
0 1 0 OO7
2 S 0 OO4
12 0 OQS
<3 0 Old
45 0.119
3 11 0 038
.11 0 12
HO 0 73
<4 0.013
2 2 0.004
1 5
2 9 0.021
9 8 0.030
06 fl 003
140 0 082
0 9
1.2 0 022
1 4 0 016
Ton
of Million
fuel1 Blu
0 16 0.47
0 11
Oil
o ie
3,5
1.0 0 30
3 3 0.3«
21 0.11
0.51
0.31
0.17
0 44
0 82
1.2 0 03
0.14 0 14
3-S 0 ID
0 35
ID 0 00
0 74 0.06
SUMMARY - HEAT
Benzo(g,h,i}-
Anthoji-
Too Ppm Too Too
of by Million ol Million of
fuel- Vol. Btu fuel- Blu Itaf
II 1490
405
2030
8.3 505
0 8 17S
32 80
1260
T2 188
125
17 14
35
1 3 I
a i
7.3
16 0
4.1 0
2.8
3.72 §8 1.3 X 10-' 30 X IO-"
1 00 28 0.9 X ID'* ft X 10 -•
6.11 140 1.4 X 10~* 33 X 10-4
2.» X 10-' 80 X lO-«
21 X 10-' 5SO X 10-'
S.3 82 3.8 X 10-' 100 X IO-«
1 2 32
0.54 15
3.0 116 O.93 X 10-< 24 X 10 -«
1.1 48 7.4 X 10-' 88 X 10-<
0 35 14 I.I X 10-' 02 X IO-<
0.12 4.8
0.40 18 «. 4 X 10-' MO X 10 -•
0.08 3 5.8 X 10-' 23O X 10 -•
0.8» X 10-< 41 X 10-«
22 X 10" 10O !<>-•
0 0 2 4 X 10— 110 X IO-«
0 0 t.l X 10-' 5.1 X 10-'
28 X 10-' 1»0 X IP-"
GENERATION SOURCES
Anthra-
Perylene perylene Ihrene Coroene cene
Mierograma Per Million Btu Heat Input
1 ,000
4,.'iOO
.'.80
IK). ouo :iix).oot>
:ux>
1 .S1NI
2UO
1,
90,000 30,
*2
200 .i .
370
2fi
330 850
200
000 400,000
100 3,900
14
300
CrouD "
Ben»-
Phenac- Fluoran- anthra-
threne thene oead
180 10
550
680
360
10,000 38,000 3000
1,000 3,200
29,000 47,000 560
1,000,000 1,000,000
56
1 ,800 270 27
3,500 1,900
8,900 5,000
7fi
15,000
100
2,900
320
77 110
* "Less than" values fcr benzo(u)pyrtm- were c.ilculated for those aim pics having C4rm>»ntraiiuns brlow t
calrulni ions were not inchulucl for ihe r>ihpr pn\\ nin-lear hydrocnrhonH ; indicated by blanks in t)ie uihle
b Mirrn|crajiis (>er J'KXj cubic inel»;rs of line iroa at slumlanl r-mdiU'trid TOT. 1 rvtino^pi^rt1 ).
p limit (tf quitnlit&tivfi determination (approximately 0.6 mirrograni per sample). Siroilar
-------
Table 4, DESIGN AND OPERATIONAL SUMMARY, INCINERATION AND OPEN-BURNING SOURCES
r
Kaled f!rate
rsourre Capacity. Area. l>uat
No. Type of ['nit Tons/Day Ft' Collector
Muniripal Incinerators
2O Multiple rhamber. 2.5U 288 Settling
traveling grate (con- chamber
tinuous fefd)
21 Multiple chamber, hatch 50 85.5 Water
charged, reciprocating spray
stoker grates scrubber
Commercial incinerators
22 Single chamber 5.3 13 None
23 Multiple chamber with 3 18.7 None
auxiliary gas burner in
primary chamber
24 Open Burning
25
26
27
In breeching.
b ID furnace.
In stack.
Table 5. POLLUTANT EMISSION
...
* - - -fuel ("liurKiiiR L'nilrrfir*- i:\r«-iKs Cua
MoiBlun- Hate \ir. Mr. Tprnft . Sin-(k-.
TyP** foment. f,'n Turts ' 1 'oy '~( '", f ^ ','< O parity
Residential rpfust 3.1 L'tlit h'> 1 8-> I'J >f>1' -f'
(14 lo 20% non-
combuatibl«)
Reaidentifcl and com- 25 -19 M)-CO 10£B 147(>-
merciftl rrfuae
(14 to 20% oon-
(conibustlble)
Cardboard, pack- 20 47 0 'ifl.V 1300* 0-2(1
ing era tea
607o paper 50 2.3 IR.W* ft-.W
4O% wet garbage
MuoicipaJ refuw 20 20-10(1
Automobile tirea 'JO-HHJ
Glwa clip pi nc«. V'O 100
leave*, tre*
branches
Automohile bodies 20-1OO
SUMMARY - INCINERATION SOURCESa
Hydro-
carbons Oxides of
Source
No.
20
21
22
23
COj O, Lba Per % Benzene Monoxide methane) (as NO»)
Flow Temp. H,O Dry Basis TOD of Soluble
Type of Unit Sampling Point scfm - °F % % % 1000 Lh* Refuse Organic* Lbs Per Ton of Refuae
Municipal
250-Ton/Da}- llreeching (before ,V2.000 1270 8.8
Multiple chamber settling clumber)
50-Ton/Day Breeching (before 5.400 1470 9. 1
Multiple chamber scrubber)
Slack (after 12.700 420 12.4
scrubber)
Commercial
5 . 3-Ton/ Day Stark 1 , 075 1 000 9.5
Single chamber
3-Ton/Day Stuck 580 070 U . 3
Multiple chamber
6. a 13.7 -J.I 18- 0.32 0.67 17. a O.CG 4.1 1.3 4.3 0.45 1.6
3.3 Hi t O.illi G.6 4.4 25 3.6
Formal-
dehyde
0.0014
0
0
0.016
• Hlunka in the table indicate that nu test was made. b Founds particulate per IO(IU pounds dry flue gaa adjusted lo 00' i exce-a air. ' I'lirtii ulule loading in breeching adjui
emission from slack. d Measured by hexane-sensitizeti nondiapersive infrared analyzL'r; reportwl HS methane.
mteJ to indicate
-------
Table 6. POLYNUCLEAR HYDROCARBON EMISSION SUMMARY - INCINERATOR SOURCES*
Source
No. Type of Uni(
Municipal
20 2SO-Ton/Day
Multiple chamber
21 50-Ton/Day
Multiple chamber
Commercial
22 5.3-Ton/Day
Single chamber
23 a-Ton/Day
Multiple chamber
•Sampling
Point
Breeching (before
settling chamber)
Breeching (before
scrubber)
Stack (after
scrubber)
Stack
SUck
• A blank in the table for a particular compound indicate*
Benzo(a)pyrene
Hfm per
1000 \I'.Jk
1U 0.075
2,700 6.1
17 0.089
11,000 53
52,000 260
it waa not detected i
k Microgram per 1000 cubic m«ter> ot Hue gu at standard condition* (70°F, 1
Pyrene
8.0
52
2.1
320
4200
n the aainple.
atmosphere).
Ben*o(e)-
pyrene Perylene
Mici
0.34
12
0.5S
45 3.1
260 60
Benzo-
(g,h,i)-
perylene
•ograms Per
34
0 63
90
870
Anthaa- Ajathra-
threne Coronene cene
' Lb of Ftcfujic Charged
0.24
15
0.63
6.6 21 47
79 210 86
GrouD 2
Pheoan- Fluoran-
thren* tbene
9.8
18 4.0
3.3
140 220
59 3900
*•*•)•
tmttak-
O.J7
0.15
4.»
•0
Table 7. POLYNUCLEAR HYDROCARBON CONTENT OF PARTICULATE MATTER EMITTED - INCINERATION
AND OPEN-BURNING SOURCESa
Source
No.
20
21
22
23
24
25
26
27
Type of Unit
Municipal incinerators
250-Ton/Day
Multiple chamber
SO-Ton/Day Multiple
chamber
Commercial incinerators
5. 3-Too/Day Single
chamber
3-Ton/Day Multiple
chamber
Open Burning
Municipal refuse
Automobile tires
Cirass clippings, leaves,
branches
Automobile bodies
oampung romi
Breeching ( before
settling chamber)
Breeching ( before
scrubber)
Stack (after
scrubber)
Stack
Stack
In smoke plum£
Bento(a>-
pyrene
0.016
3.3
0 15
58
180
11
1100
35
270
Pyreae
1.9
28
3.6 .
350
2600
29
1300
120
670
Benzo(e)-
pyrene
0.08
6.5
0.97
49
ISO
4.5
450
21
120
BenaXghi)-
Perylene perylene
aiicTograniB r
19
1 .1
3.3 98
36 540
72 660
5.4
33 150
Anthan-
threne Conmeae
er oram 01 r arucuiai
0.06
8.2
1.1
7.1 23
45 130
53 81
12 15
Anthra-
cene
51
53
4.7
110
4.7
220
Pbenan-
Umne
0.8
150
62
450
160
Fhioran-
Um>
2.2
2.5
5.5
240
2400
13
470
J10
450
antbnoM
O.OB
0.26
6.0
210
SAO
25
40
' A blank in the table for a particular compound iadJcata it wt» not detected in the (ample
-------
Section 9
SPECIAL TOPICS
Test Methods for Determining Emission
Characteristics of Incinerators
-------
TEST METHODS FOR DETERMINING EMISSION
CHARACTERISTICS OF INCINERATORS
Fred R. Rehm
I BACKGROUND INFORMATION
Many people close to the field of incineration
have long appreciated the pressing need for
standardized techniques and test methods for
determining the air pollution emission char-
acteristics of incinerators. Those who would
be greatly concerned and affected by such test
standards include incinerator designers, manu-
facturers and consultants, along with the people
working in the field of governmental air pol-
lution control. It is generally conceded that
it is one of the functions and responsibilities
of this latter group to assess and to evaluate
these and other air pollution emissions. It
has been stated that not until standardized
test methods are adopted and accepted will
standardized emission limitations for incin-
erators be possible and truly meaningful. The
incinerator manufacturers have regularly
striven for standardized air pollution regula-
tions to aid them in achieving standardized
production models of incinerators and lower
costs.
When one considers the problem of inciner-
ator air pollution emission charactistics,
early attention must be given to defining the
type discharges which are of greatest con-
cern. It is this Sub-Committee's conviction
that we are principally interested at this
time in the following three categories of
incinerator effluents - visual emissions
(smoke), particulates, and odor. It is in
these three areas that the greatest present
need exists with respect to air pollution per-
formance evaluation standards or limitations
and standardized test methods. With the
heterogeneous nature of refuse being incin-
erated and hence the wide range of gaseous
effluents possible - and the increased atten-
tion being directed to the health aspects of
air pollution, we may some day direct ad-
ditional attention to these gaseous discharges.
However at this stage of the science of air
pollution control, we must of necessity di-
rect our principal attention to the nuisance-
type discharges that have plagued the
development and improvement of this class
of combustion equipment. It is toward the
standardization of testing of these three
classes of incinerator effluents that this re-
port is pointed.
II VISUAL EMISSION TESTING
Almost everyone who has workfd with com-
bustion processes and is familiar with the
basic requirements of air pollution control
ordinances, must of necessity be familiar
with the Ringelmann Chart, as published by
the U.S. Bureau of Mines, and its use in
assessing the visual or smoke emissions
from incinerators. From a strictly scientific
standpoint, the Ringelmann Chart leaves much
to be desired in our efforts to quantitatively
assess visual effluents. Nevertheless, its
use is practically basic in the field of air
pollution control and in the smoke control
programs which were the forerunners of the
present day expanded air pollution control
efforts. Until some better, more practical
tool evolves, the Ringelmann Chart will un-
doubtedly continue to serve as the most fre-
quently used method for assessing visual
smoke emissions from incinerators and all
other combustion processes. Numerous
discussions on the use of the Ringlemann
Chart appear in the literature and it is not
out intention here to belabor the use of this
test method on visual incinerator effluents.
In recent years, a refinement has been intro-
duced to the test methods used in the visual
field which permits the grading of colored
effluents other than shades of black and white
as intended by the Ringelmann Chart. Even
this improvement or refinement device, which
is frequently referred to as the "opacity" of
a visual emission, is usually compared with
an "equivalent Ringelmann density" as its
standard. Opacity assessment is related to
the ability "to see through" a column of
smoke. Visual black smoke emissions have
not generally been a serious problem in re-
fuse incinerator operation. Off-color visual
PA.C.ce.9. 1.66
-------
Test Methods for Determining Emission Characteristics of Incinerators
discharges which could be more readily graded
on an opacity basis are the more usual type
visual effluents emanating from refuse in-
cinerator operation. Widespread application
and enforcement of an opacity limitation by
air pollution control agencies on incinerator
discharges, undoubtedly, would have a signi-
ficant effect on future incinerator designs.
In recent years, some interest has been shown
by a few incinerator investigators in the use of
paper tape filters and photoelectric devices to
measure smoke or visual effluents. The mov-
ing paper tape sampler is said to have a number
of advantages in measuring smoke emissions.
One obvious advantage of both the moving tape
filters and photoelectric devices is the continu-
ous smoke performance record such systems
provide. Photoelectric smoke measuring de-
vices have been used quite successfully in com-
bustion processes where oil and coal are burn-
ed. This class of smoke measuring device has
seen little usage in the incinerator field - the
main exception being in new municipal incin-
erator plants where this type smoke measuring
device is often incorporated. The high cost
and the lack of portability of this type equip-
ment mitigates against its use as a field
measuring tool.
Ill SURVEY CONDUCTED
In May 1961, the Air Pollution Control Associ-
ation TA-3 Incinerator Committee took cogni-
zance of the need for a review and study of the
test methods which had been, and were being,
used by investigators working in the inciner-'
ator air pollution field. It was hoped that such
a review and study might ultimately lead to a
recommended standardized test procedure
for certain categories of pollutants. The
actual study and review of incinerator test
methods was delegated to the Performance
Evaluation Sub-Committee of the parent In-
cinerator Committee. It was agreed that this
group would most profitably concentrate its
efforts in the particulate and odor emission
categories. Accordingly, the Performance
Evaluation Sub-Committee queried representa-
tives of various groups or organizations for
the names of people or groups who had pre-
viously, or were known or suspected to be pre-
sently, engaged in the measurement of incin-
erator particulate and odor emissions. Interest
was expressed in all classes and sizes of
incinerators ranging from domestic to muni-
cipal. Some of the groups contacted were:
Air Pollution Control Departments
American Gas Association
Commercial and Industrial Incinerator
Manufacturers
Domestic Incinerator Manufacturers
Incinerator Institute of America
Municipal Incinerator Consultants
Municipal Incinerator Contractors
Research Organizations
U.S. Public Health Service
The result of this survey produced the names
of 43 different individuals or groups who were
said to have displayed a proficiency in the
field of incinerator particulate or odor mea-
surement. Subsequently, a carefully pre-
pared questionnaire was sent to each of the 4'3
parties querying them on the details of the
test methods they used in their incinerator
studies and requesting that they comment on
the advantages and disadvantages of the test
methods they favored. Of the 43 persons and
organizations queried, replies were received
from 32. Of the 32 replies, only Hi groups in-
dicated that they have had extensive experience
and familiarity with incinerator particulate or
odor measurement. The results of the second
phase of this survey were most revealing in
that it was apparent that only a very small
number of groups or individuals had first-
hand knowledge, familiarity and experience
in the incinerator particulate or odor test
field. This finding seems very incongruous
and disturbing since refuse incineration has
been frequently described as being one of the
larger contributing sources to a community's
air pollution problem.
IV ODOR TESTING
The results of the survey of the Performance
Evaluation Sub-Committee have been tabulated
and are now under study by this group. A cjopy
of the tabulation is appended to this report.
One of the findings this survey disclosed.was
-------
that only a limited amount of work has been
conducted on odor testing of incinerator
effluents with the exception of the domestic
incinerator size ranges. In the domestic in-
cinerator field, odor measurement and testing
has principally been performed by using the
American Gas Association, Inc., and Ameri-
can Standards Association, Inc., open burning
newspaper technique.1 (1) In this method,
three observers smell the gases produced by
the burning of two sheets of newspaper in an
open container. Then, at 15-minute intervals,
they enter the incinerator test room from the '
outside and compare the odor from the gases
aspirated from an AGA test stack with that of
the two burning sheets of newspaper. It is
obvious that this test method suffers from the
inconsistencies, differences and subjectivity
of the human olfactory mechanism. Modifi-
cations of the AGA incinerator odor panel
technique have also been described in the
literature. All such systems rely on the hu-
man nose as the test instrument. The newest
and a most promising odor measuring tech-
niqud developed for domestic gas incinerators
was recently reported by Battelle Memorial
Institute. (2) In this test method, it has been
demonstrated that the carbon monoxide (CO)
concentration in incinerator emissions may
be used as a valid, objective indicator of the
odor intensity of domestic gas-fired inciner-
ator effluents when burning an A. S. A. domes-
tic waste charge, including both the olfactory
(smell) and trigeminal (pain or irritation)
components.
In the commercial, industrial and municipal
incinerator field, the few investigators re-
porting a quantitative concept of odor mea-
surement strongly favored the ASTM Standard
Method for Measurement of Odor in Atmos-
pheres (Dilution Method) D 1391-57. In this
method, a sample of the gas, whose odor is
to be measured, is diluted with odorfree air
until a dilution is reached in which an observer
can barely perceive the odor. The ratio of the
total volume of this diluted sample to the
volume of original sample in the diluted sam-
ple, is a measure of the concentration of
odor in the original sample. This technique
assumes that the odor concentration is to be
measured without regard to the material or
materials that cause the odor, or the concen-
tration of these causants. It also does not
take into account the character of an odor.
A number of investigators have reported
a relationship may exist between the con-
centration of carbonyls (aldehydes and ke-
tones) in incinerator effluents"and odor levels.
From the above findings, it would appear that
an incinerator odor test method based on the
ASTM Standard D 1391-57 may h<- generally
acceptable in other than the domestic gas
incinerator field where the Battelle CO method
appears to have much merit.
V PARTICULATE TESTING
The greatest amount of incinerator emission
test work that has been performed has been
done in the particulate emission field. Of
the 16 groups supplying detailed information
on incinerator particulate or odor testing,
15 reported having conducted tests on parti-
culate emissions, while only 11 reported con-
ducting odor measurements. Of this group
reporting on odor measurements, the ex-
perience of seven of the 11 respondents was
limited to the domestic incinerator field. An
analysis of the particulate test methods used
by all reporting investigators showed they
could be grouped into three general type
categories. One test technique can be
described as the so-called American Gas
Association, Inc. or American Standards
Association, Inc. testing scheme which has
been used almost exclusively in the perfor-
mance testing of domestic incinerators not
exceeding 4-bushel capacity. This test
method is detailed in the American Standard
Association, Inc., publication "Approval Re-
quirements for Domestic Gas-Fired Incin-
erators. " The second general test category
which has been used involves the low sam-
pling volume technique (less than two cfm);
this is a modification of the procedures out-
lined in the Western Precipitation Corporation
Bulletin WP-50, "Methods for Determination
of Velocity. Volume, Dust and Mist Content
of Gases. " The third general type test tech
nique which has been used is the large sam-
ple volume method (greater than two cfm);
this is a modification of the procedures out-
lined in the ASME Power Test Codes PTC
27-1957, "Determining Dust Concentration
in a Gas Stream" and PTC 21-1941, "Dust
Separating Apparatus. "
-------
Testing Methods for Determining Emission Characte
jf Incinerators
Ideally, it would be preferable to utilize a
test method which gave instantaneous readings
of dustloadings of effluent gas streams. Un-
fortunately however, such a method or tech-
nique has not been developed as yet. An in-
stantaneous dustloading test device would
greatly reduce the effort and vagaries in
assessing the effect of the many variables in
the incineration of refuse. The variables
which have been suspected or reported as
affecting the air pollution performance of an
incinerator are almost as numerous and
varied as is the character of the refuse
charged to an incinerator. Through such a
test device, it would be possible to rapidly
assess the effect of design parameters, air
supply and distribution, refuse characteristics
and operating procedures. As it is, all of the
three test methods presently in use must rely
on reporting average dustloading test results.
All three of the previously mentioned parti-
culate test methods incorporate the following
basic requirements. They vary, however, in
the manner in which these basic requirements
are achieved.
A Securing a truly representative sample
of the gas and suspensoid from the main
gas stream.
B Filtering of the particulates from the
sampled gas stream.
C Accurately measuring the sampled gas
volume.
D Making such other measurements as are
necessary to assess the total emission
characteristics. These include tempera-
ture, pressure, gas velocity, gas com-
position, molecular weight and density.
Analyzing each of these four basic require-
ments in terms of the three general particu-
late test methods reported as being used, it
was discovered that the main divergence'of
method and technique occurs in the securing
of a truly representative gas and particulate
sample. The problem of securing a repre-
sentative gas and suspensoid sample would
be eliminated if it were practical to use the
total gas flow as the sample stream. This
is not a practical approach due to instrument
size and portability requirements. Failing
to secure a truly representative effluent
sample by any of the three methods reported
as being used will yield meaingless results
no matter how refined and accurate are the
mechanics and techniques of determining the
other three basic test requirements.
The very nature of the AGA, Inc., and
ASA, Inc., test facility and test method leaves
it wantmg for consideration as a standardized
test method for all size ranges of incinerators.
This test technique was designed to evaluate
the air pollution performance of highly de-
fined and confined conditions of design, con-
struction, refuse materials and conditions
of operation. This test method provides fora
standardized test stack arrangement, a fixed
gas sampling rate, fixed position sampling
in the small test stack, standardized refuse
charge compositions and specific operating
cycles. For the express purpose for which
it was developed, this test method appears
to be well conceived. This type test method
however, does not lend itself well to wide-
spread usage in the commercial, industrial
and municipal incinerator field due to the
physical size of these classes of incinerators
the great number of "on-the-spot" constructed
incinerator installations, the lack of stand-
ardization of designs caused by the widely
varying needs and requirements for these
classes of incinerators, the wide range of
composition of refuse normally handled by
incinerators of,these classes and the wide
range of operating procedures practiced in
field installations. A standardized test
facility and test method of this same general
type could well serve the needs of an incin-
erator manufacturer to evaluate the effect
on air pollution performance of developmental
changes and modifications on some of the
smaller commercial-sized incinerators. It
is our understanding that the American Gas
Association has under consideration the
development of a standardized test facility,
test methods and approval requirements for
small commercial-sized refuse incinerators.
In setting up such a standardized test facility
and test methods, special consideration
should be given to representative effluent
sampling for particulates when dealing with
these larger sized incinerators where strati-
fication problems are likely to occur in a field
installation due to widely varying design, refuse
and operating conditions.
-------
Test Methods for Determining Emission Characteristics of Incinerators^
The use of adhesive coated paper for the
estimation of particulate incinerator emissions
has been reported within the past year. At
least one community has established an or-
dinance emission limitation based upon the
utilization of the adhesive coated paper esti-
mating procedure.
] Representative sampling
The remainder of this report will be
limited to a discussion and analysis of
the modified dustloading test methods
outlined in the ASME Test Codes and
the WP-50 Bulletin which were report-
ed as being used by various incinerator
investigators. It is apparent that the
WP-50 Bulletin test method describes
the use of field test equipment which
has a maximum sampling rate of
approximately two cfm. Whereas the
ASME Test Codes do not favor or pro-
mote the use of any particular type
test apparatus, they were obviously
written or directed toward power plant
testing. Due to the widely varying
particle size and chemical composition
of incinerator particulates, special
emphasis must be placed on the prob-
lem of securing representative gas and
suspensoid samples in incinerator
testing. As long as most air pollution
dustloading limitations are directed at
the "nuisance producing potential" of
the effluents rather than on health
effects - or other aspects, it must be
possible to assess such potential in any
test method that is proposed as a
standard. This requires the sampling
of the large sized incinerator char
particles which are a most frequent
cause of incinerator particulate com-
plaint, as well as the smaller sized
particulates. It has been suggested
that sampling nozzles should be a mini-
mum of 3/4 inch inside diameter in
order to capture and sample most in-
cinerator char and flake material. The
larger the size of the sampling nozzle
used, the less the likelihood of biasing
against the larger sized particulates.
Work conducted by Armour Research
Foundation3 at the Chicago Calumet
Incinerator has substantiated and
corroborated this biasing effect in
the use of small sized nozzles for sam-
pling incinerator particulates. With
conventional design incinerator breech-
ing and stack velocities now being used,
a minimum sampling nozzLe diameter
limitation of 3/4 inch would also pre-
clude the use of the low volume sam-
pling train and equipment described in
the WP-50 Bulletin, if isokinetic sam-
pling is to be achieved. Limiting fac-
tors affecting the size of the sampling
nozzle to be used will be the availability
of an adequate suction or aspirating
device to "isokinetically" sample at
the nozzle opening, the pressure drop
across the sampling train and the size
and portability of the sampling apparatus.
Incinerator breeching and stack veloci-
ties can range from J5 feet per second
to 90 feet per second.
The matter of "isokinetic" sampling is
a particularly acute problem in inciner-
ator test work, principally due to the
method and type charging procedures
used and the variable nature of the re-
fuse being burned. Both of these fac-
tors have a significant effect on the
temperature and velocity characteristics
of an incinerator system. Even with
the new continuous feed municipal in-
cinerators, the variable nature of the
refuse causes rapid gas temperature
and velocity changes in the system.
Another recent innovation affecting
municipal incinerator system velocities
has been the use of variable speed in-
duced draft fans. Such fans have been
used to compensate for rapidly changing
refuse characteristics and to help main-
tain steady state draft conditions. This
type draft-producing system further
complicates the problem of isokinetic
sampling. It has been a generally ac-
cepted fact that invalid dustloading
test results are obtained when true iso-
kinetic sampling is not realized. Non-
isokinetic sampling results in the
securing of n on-representative gas
and dust samples. Due to the rapid and
frequent velocity changes in an inciner-
ator system, some investigators have
-------
Test Methods fojvDetermining Emission Characteristics of Incinerators
found it a practical necessity to use the
null "static balanced tube" method of
testing to secure representative sam-
ples. In this type sampling, the velocity
of the gases entering the sample nozzle
is continually adjusted to equal the
velocity in the duct or stack at the sam-
pling location. In the alternative sam-
pling method, velocity head and tem-
perature changes at the sampling point
are translated to changes in the gas
sampling rate. Considerable time is
lost and needless error is introduced
in the period it takes to mathematically
and actually translate these system
changes to the physical sampling system.
Significant sampling errors are likewise
introduced in incinerator testing when
one uses a fixed gas sampling rate based
on a velocity determination that was
made a matter of 15 minutes to 60
minutes before the dustloading test
period. Such procedure ignores the
dynamic nature of the incineration
process.
Sampling location is an important con-
sideration in any particulate testing. It
is even more important in incinerator
testing where sizeable percentages of
the particulates are above 44 microns
in particle size. Both the ASME Test
codes and the WP-50 Bulletin recom-
mend sampling in vertical flow ducts.
In incinerator installations, this usually
means the stack. Sampling at such a
location reduces the possibility for
error introduced by dust and gas strati-
fication. There is practically no sub-
stitute for experience in selecting a
suitable sampling location. Some
incinerators provide relative freedom
from stratification in three to five
stack diameters above the top of the
breeching saddle where other inciner-
ators have required five to 10 stack di-
ameters to produce the same results.
Horizontal ducts and breechings of in-
cinerators are particularly prone to
dust stratification problems. Accessi-
bility and room for freedom of move-
ment at a sampling location are im-
portant considerations in the placement
of test openings.
Even with wise and proper selection
of the sampling location, it has been
found important that ample and adequate
traversing of the stack or duct be per-
formed. Both the ASME Test Codes
and the WP-50 Bulletin agree that
adequate traversing of the stack in
dustloading and velocity tests is neces-
sary. The Sub-Committee, whole-
heartedly, concurs with this recom-
mendation. The suggested minimum
number of sample points outlined in
the ASME Test Codes for various cross-
sectional areas appears to be satis-
factory. The need for additional sam-
pling points in traverse of a stack or
duct for any particular test is a deter-
mination that is best made on the basis
of each individual situation.
Due to the relatively high temperatures
in an incinerator system, it is almost
mandatory that water-jacketed stainless
steel probes be used for dustloading
test work. Water jacketing of the probe
serves a number of purposes. It pre-
serves the sampling probe and thus re-
duces the errors caused by the cor-
rosiveness of the sampled gases. It
cools and reduces the combustion losses
of the sampled particulates as many of
these particles are aglow when sampled.
It permits the use of lower temperature
range filtration media. In-stack filtra-
tion of the sampled particulates is not
recommended for incinerator test work
due to the combustion losses suffered
as a result of the high stack tempera-
tures. Even water-cooling of the fil-
tration media holder often fails to
arrest combustion losses of the sam-
pled particulates when in-stack filtra-
tion is used.
2 Filtration media
The principal area of difference between
the ASME Test Codes and the WP-50
Bulletin with respect to filtration media
results from the basic difference be-
tween a high and low volume sampling
rate test method. Both recommended
that high particulate filtration efficiencies
be achieved. Both techniques agree that
-------
Test Methods for Determining Emission Characteristics of Incinerators
pressure drop across the filtration
media is an important limitation in
sizing the sampling train. Both methods
suggest a high catch to weight ratio for
the filtering media. A problem peculiar
to incinerator sampling is the relatively
low concentration of participates en-
countered and the high percentage of
water vapor present in incinerator
emissions. The combination of these
two conditions, along with others, makes
the selection of the filtration system and
filtration media a difficult one. The
necessarily high gas volume sampling
rate, the relatively low dust concen-
tration, the high moisture content of
the gases, the need for high separation
efficiency at relatively low pressure
drop, the weight stability of the filtra-
tion media, the ruggedness requirement
for field usage, the high gas tempera-
tures and a test system portability re-
quirement are a number of considerations
that go into the selection of the filtration
device and filtration media. It is most
difficult to find a filtration device and
media providing optimum characteris-
tics in lieu of all these considerations.
It is often necessary to compromise on
one or more of these considerations in
selecting the system and media. If un-
due emphasis is placed on the high sam-
ple catch to filter weight ratio require-
ment for the filtration media, the length
of a dust test run would be unreasonably
extended in view of the relatively low
dust concentrations. A medium which
is light in weight and needing most of
the other criteria suffers from lack of
ruggedness for use under trying field
conditions. The high water vapor con-
tent of incinerator gases also present
serious problems for the lighter weight
filtration media. Heat jacketing of the
filtration media holder has been sug-
gested as a means to minimize filter
condensation problems. Temperature
limitations of various filter media has
been adequately treated in the ASME
Test Codes. It has been suggested that
a dual filtration system, consisting of
a small diameter cyclone followed by a
fabric filter, is a satisfactory com-
promise arrangement. The cyclone
tends to precipitate the larger sized
particulates from the sampled gas
stream as well as serving as an entrain-
ment separator for any condensed or
entrained moisture. This permits use
of the filter media without undue pre-
sure buildup due to condensation. This
arrangement is particularly suitable
for evaluating wet scrubber dust col-
lector systems which have found wide-
spread application in the municipal
incinerator field. This type arrange-
ment requires considerable filtration
media weighing technique to minimize
errors caused by the hygroscopic ten-
dencies of a fabric filter.
3 Measuring sampled gas volume
The principal differences between the
ASME Test Codes and the WP-50
Bulletin techniques with regard to mea-
suring the sampled gas volume also
revolves about the discrepancy in sam-
pling rates for each method. Emphasis
seems to be placed in the ASME Test
Codes in the use of orifice-type gas
metering devices. The WP-50 Bulletin,
in contrast, seems to encourage the use
of dry gas meters. Either method is
satisfactory if proper precautions are
taken to insure the accuracy of the
equipment used. At the high gas sam-
pling rates associated with the larger
sized sampling nozzles needed to secure
a representative sample in incinerator
testing, the required size of a dry gas
meter would be cumbersome, and may
be unmanageable in a field test. The:
WP-50 Bulletin treats the matter of
measuring the high moisture content of
incinerator gases in a more thorough
manner than does the ASME Test Codes.
The measurement of the water vapor
content of incinerator gases is especially
important when any special type dust
collection system has been provided.
The need for water vapor measurement
applies especially to incinerators that
use wet scrubber or mechanical cen-
trifugal dust collector systems. Water
spray systems are often used in me-
chanical collector installations to cool
-------
Test Methods for Determining Emission Characteristics of Incinerators
the incinerator effluent gases to within
the temperature limitations of the dust
collector and the induced draft fan.
4 Supplementary measurements
Neither of the test methods that have
been discussed adequately treat the
problem of making supplementary mea-
surements needed to complete a dust-
• loading determination in light of the
presently used methods of expressing
the results of such tests in terms of
excess air or carbon dioxide adjustment
or correction. Most dustloading limita-
tions that are being enforced by air pol-
lution control agencies these days include
provision for some such correction.
Some investigators have suggested that
any correction or adjustment of test re-
sults be limited to an excess air basis
reported in terms of the oxygen content
of the effluent gases. It is not the Sub-
Committee's intention to argue for or
against the merits of the presently used
practices of adjusting and reporting test
results at this time. It has been our ex-
perience that a well-designed, engineer-
ed, constructed and operated incinerator
is capable of performance within the re-
quirements of most of these stringent
limitations embodying either a 12% CO2
or 50% excess air correction, if effective
provisions are incorporated in the unit
to reduce particulate loadings. Any test
method for measuring particulates in
incinerators must take cognizance of the
rapidly changing gas analyses and ex-
cess air conditions encountered in the
incineration process, particularly with
presently used incinerator designs and
operating practices. These wide vari-
ations in gas analyses and excess air
conditions exist in the newer continuous
feed incinerator plants, as well as in
the batch charge type units. Because
of these rapidly varying analyses, it
is necessary to use continuous gas
analyzing equipment to measure these
dynamic conditions. It has been report-
ed that either, or both, continuous car-
bon dioxide analysis or continuous oxygen
analysis equipment is desirable to ac-
curately assess and measure these
variations. The continuous gas sam-
pling equipment should be backed up
by regular Orsat gas analyses. TheOrsat
analyses check the proper functioning of
the continuous gas analyzers as well as
providing data for gas molecular weight
and density calculations. Some investi-
gators have collected integrated gas
samples over either a salt or acidified
sodium sulfate solution for the full
period of a test run and then have con-
ducted Orsat analyses of these com-
posite samples. The detailed infor-
mation gained by the continuous gas
analyzers may well be worth the extra
cost and inconvenience of using this
additional equipment. By taking fre-
quent readings of the continuous gas
analyzers, the need for a continuous
recorder is minimized. Recording
equipment is not readily portable and
is often not sufficiently rugged to with-
stand the rough treatment and condi-
tions encountered in field testing. Re-
cording equipment also adds appreciably
to the cost of making a test determination.
It was the feeling of many of the investi-
gators that it would be impractical and
meaningless to try to standardize on
refuse charges and charge cycles for
commercial, industrial and municipal
incinerators as part of an overall stan-
dardized test method for determining
emission characteristics. We are all
cognizant that incinerator refuse ma-
terial is completely heterogeneous and
that it varies from charge to charge,
day to day and from city to city. Re-
commended operating practices and
procedures will also vary widely from
one design unit to another making a
standardized charge cycle a synthetic
practice that has little significance.
Any standardization in the test method
from a refuse and refuse charge stand-
point might well be limited to testing
the emissions under rated capacity and
in accordance with the recommended
conditions and procedures of the in-
cinerator manufacturer. Some investi-
gators have suggested that performance
tests be principally conducted during
the period of stable operation of the
incinerator. These conditions and
-------
Test Methods for Determining Emission Charactei
af Ir
Drs
operating procedures could then be
detailed in the test report.
In summary it is the Performance
Evaluation Sub-Committee's opinion
that the ASME Test Codes PTC 21-
1941, "Dust Separating Apparatus" and
PTC 27-1957, "Determining Dust Con-
centration in a Gas Stream, " with
modifications and additions as discuss-
ed, could form the basis of an acceptable
standardized test method for determining
incinerator particulate emission
characteristics.
a "Approval Requirements for Domes-
tic Gas-Fired Incinerators" Z 21.6-
1957 American Standards Association,
Inc.
b "Development of an Odor-Measure-
ment Technique for Domestic Gas
Incinerators" - Battelle Memorial
Institute Project DAG-4-M.
c "Sampling Studies on Emissions from
Municipal Incinerators" - Armour
Research Foundation Project C832.
Summary of Survey on Incinerator Particulate
and Odor Testing by Performance Evaluation
Sub-Committee of APCA Incinerator
Committee TA-3
In the following summary, an abbreviated
form of heading is used to avoid needless
repetition. Following is a complete expla-
nation of these abbreviations:
Code_- The test code or standard followed
by this organization, group, or
individual.
Probe_- The sampling probe and its iso-
kinetic features.
Filter - Filter media employed.
Gas_- Sampled gas measurement (parti-
culate testing).
Vacuum - Vacuum production (particulate
testing).
Velocity - Velocity determination (parti-
culate testing).
Incinerator - Size and type tested.
Charges. Charging - The standardized
charges and charging used.
Method - Odor method used and comments.
-------
Test Methods for Determining Emission Characteristics of Incinerators
American Standards Association^ Inc. Appro-
val Requirements for Domestic Gas-Fired
Incinerators.
Code: ASA, Inc., Approval Requirements for
Domestic Gas-Fired Incinerators.
Probe: ASA. Pyrex glass - 1 in. I. D. X 48 in.
long. Fixed sample rate - 35 ft3/hr. Fixed
duct - 8 in. X 10 in. Fixed position - no
traverse. Probe flushed. One sample flow
rate adjustment for temperature at start of
test.
Filter: ASA. Unimpregnated glass wool filter
paper. MSA type 1106B. Cat. no. CT-25310.
Two weighed without drying initially. One
used. After run, store at room tempera-
ture alongside blank. Weigh. Record gain
in weight with blank correction.
Gas: ASA. Calibrated thin plate square edged
orifice with slope gauge. 35 ft3/hr (120°F).
Temperature correction three times in 15-
min test run.
Vacuum: ASA. Tank type vacuum cleaner
blower and motor. Equiv. to Lamb Elec-
tric #4450.
Velocity: No determination.
Advantages: 1) Developed after much study
and developmental work. 2) Relatively
simple and inexpensive equipment.
Disadvantages: 1) Requires trained and
skilled personnel.
Incinerator: Domestic.
Charges: ASA. 1) Mixed refuse (weights in
ounces): Food refuse - white potatoes 7,
cabbage 3, unpeeled oranges 2, white
bread 2, rice 2.4, beef suet 1, water 2.6;
Dry combustible - corrugated cardboard
6.6, newspaper 3.3, waxed paper 12 in.
wide 3.3. 2) Shredded newspaper lib/
bushel.
Charging: ASA. 1) Mixed refuse on specified
cycle. 2) Shredded paper on specified
cycle.
Excess Air Adj.: ASA. CO2 and 0% read by
Orsat three times in 15 min test. Average
used in calculations to a 50% excess air
basis.
ASA. Using three persons, they
,
shall smell the gases produced by burning
two sheets of newspaper. They shall enter
the incinerator room from the outside or
from a room where fresh air is present.
They shall note the presence of odor in
the room and the odor of flue gas aspirated
from the test stack. Such odor shall not be
more objectionable than that caused by the
two sheets of newspaper.
The Adams Manufacturing Co.. 1530 St. Clair,
Cleveland 14, Ohio, Mr. Harry Friedberg
(private communication).
gode: ASA, Inc., smoke filter method.
Probej^ Small probe. Fixed volume sample -
2250 + 100 in.3 gas/in.2 of filter area.
Filter: Equivalent in thickness, porosity and
whiteness to Whatman #4 paper. Smoke
recorder unit should be equivalent to:
Bacharach Industrial Instrument Co., Re-
search Applicance Co., Von Brand Co.
Gas: Sampling rate preset prior to test.
Calibrated pressure drop mechanism
across filter tape.
Vacuum: By sampler pump or plunger.
Velocity: No determination.
Advantages: Equipment is relatively simple
and sufficiently reliable.
Incinerator: Domestic.
Charges: ASA.
Charging: ASA.
Excess Air Adj. : None.
Method: Recommends Battelle odor method
of measurement of CO concentration. His
experience presently limited to ASA. New
Battelle method sufficiently accurate for
control purposes, as is ASA method.
Consolidated Natural Gas System, 1201 East
55th Street, Cleveland 3, Ohio, Dr. F. E.
Vandaveer, Director of Research.
Code: ASA.
Probe: ASA.
10
-------
Test Methods for Determining Emission Characteristics of Incinerators
Filter: ASA.
Gas: ASA.
Vacuum: ASA.
Velocity: No determination.
Advantages: Satisfactory.
Incinerator: Domestic, comm.
Charges: ASA.
Charging: ASA.
Excess Air Adj.: ASA.
Method: ASA with reference to Battelle Pro-
ject DAG-4-M.
Locke Stove Company, N. L. Martin (private
communication).
Method: ASA
The Majestic Co., Inc.. Huntington, Ind.,
Mr. Don Winegardner, Vice-President (pri-
vate communication).
Code: ASA.
Probe: ASA.
Filter: ASA.
Gas: ASA.
Vacuum: ASA.
Velocity: No determination.
Advantages: Satisfactory.
Incinerator: Domestic.
Charges: ASA.
Charging: ASA.
Excess Air Adj.: ASA.
Method: ASA.
Martin Stamping and Stove Co., Huntsville.
Ala., Frederick H. Martin, Executive
Vice-President (private communication).
Code: ASA.
Probe: ASA.
Filter: ASA.
Gas: ASA.
Vacuum: ASA.
Velocity: No determination.
Advantages: Satisfactory. If unit passes
AGA tests, it will not become an air pol-
lution nuisance.
Incinerator: Domestic:
Charges: ASA.
Charging: ASA.
Excess Air Adj.: ASA.
Method: ASA. However, feels that a repeat-
able measurement for odor is hard to attain
and not necessary. With a clear stack and
a minimum temperature of 800°F on most
incinerators (with reservations), there will
be no foreseen odor nuisance.
_Wnirlpopj_Corp_., St. Joseph, Mich., W. R.
Crawford, Research Engineer (private
communication.
Code: Modified ASA.
Probe: Tear drop probe - Diagonal in ASA
duct. Ten 1/4 in. or 1/8 in. holes - Center
point of equal area sections. Continuous
isokinetic sampling rate using fixed pitot
tube location (0.9 X center velocity).
Filter: Two layers of MSA glass fiber filter
web, Cat. No. CT-75428. Millipore filter
type holder. Developed special moisture
diffusion system to remove moisture from
sample gas line.
Gas: Calibrated flow motor and manometer.
Flow rate 0. 15 to 0. 60 cfm.
Vacuum: Cast Mfg. Corp. Model 02 11
vacuum pump, 1. 7 cfm capacity.
Velocity: Pitot tube continuously measures
velocity head. Nomographs convert to
gas velocity and volume.
Advantages: 1) Found results reproducible
and correlated with field observations.
2) Measures the particulate discharge of
five microns or under which can be classed
as "permanently" airborne and permits
calculation of the total amount discharged.
3) Measures and permits calculation of
11
-------
Test Methods for Determining Emission Characteristics of Incinerators
total participate matter over five microns
in size which will fall out on adjacent
properties. 4) Removes moisture from
particulate measurement system with a
diffusion tube which permits rapid weigh-
ing and use of efficient filter papers con-
veniently at room temperatures. 5) Pro-
cedure is based on scientific methods
giving numerical results with no opinions
or judgments involved in evaluations.
Disadvantages: 1) High cost of equipment.
2) Lacks portability in present form.
Incinerator: Domestic.
Charges: ASA.
Charging: ASA.
Excess Air^dl : Calculations based on iso-
kinetic sampling. Measured total parti-
culate. No excess air adjustments
indicated.
Method: A method was developed to dynamical-
ly and continuously analyze for odor in a
gas using the human nose as a detector.
This method employs the continuous dilu-
tion of the odorous gas with fresh air until
the smell threshold of the nose is reached.
This threshold is constant for a given ma-
terial. The ratios of the flow of fresh
air to the flow of odorous gases at thres-
hold may then be quantitatively compared
by expressing them as odor numbers. Uses
the threshold level of the human nostril as
an odor measurement reference level with
provision for simple observer training and
check out of sensitivity of observer. Per-
mits plotting a profile of odor output dis-
charged vs. time as well as an expression
for total odor generated.
Division of Smoke Regulation. Columbus, Ohio
(!951 to 1958), Herbert C. Johnson, Director
(private communication).
Code: ASME (1941) Test Code for Dust-
Separating Apparatus. Western Precipita-
tion equipment with modifications.
Probe: Stainless steel probe with different
size nozzle heads. Special pitot tube
arrangement attached to sampling probe
to provide for isokinetic sampling rate
adjustment. Traversed as per ASME and
WP-50 Bulletin requirements.
12
Filter: Fiberglass bags in holder - outside
of stack or duct.
Gas: Calibrated orifice.
Vacuum: Not stated.
Velocity: Standard pitot tube.
Advantages: 1) Equipment was relatively in-
expensive, rugged and easy to set up. 2)
Sampling time could be extended several
hours, if desired, providing dustloadings
were not unusually heavy, or the moisture
content exceptionally high. (A heater
system was finally developed which practi-
cally eliminated moisture problems). 3)
Technicians who were willing could learn
to conduct tests in a relatively short time.
Calculation of results was reasonably
simple.
Disadvantages: 1) Lack of correction for
moisture content of products of combustion.
This can be overcome by additional test
equipment and proper calculations. 2)
Percentage of samples lost from the fiber-
glass bags not known; believed collection
efficiency was 98. 0% plus for incinerator
particulates. 3) Collection of the samples
at temperatures only slightly above am-
bient in the presence of moisture con-
ceivably could result in the formation of
particulate not present in the stack.
Incinerator: Domestic, comm., mun.
Charges: Variable - field installations.
Charging^ Variable - field installations.
Excess Air Ad.1.: Periodic Orsat analyses.
Department of Air Pollution Control. Milwaukee
County. Fred R. Rehm, Deputy Director
JAPCA - Feb. 1957.
Code: Modified ASME Test Code for Dust-
separation Apparatus (1941) and Test Code
for Determining the Dust Concentration
in a Gas Stream (1957).
Probe: Stainless steel water jacketed probes
of different inlet diameter - minimum dia-
meter recommended 3/4 in. Static balanced
tube method of isokinetic sampling. Sam-
pling in vertical ducts preferred. Traverse
as per ASME Test Codes. Balanced tube
feature permits isokinetic sampling re-
gardless of widely varying flow rates as
-------
Test Methods for Determining EmissionOiaracteristics of Incinerators
experienced in incinerator testing. Large
diameter sampling nozzles - 3/4 in. to
2 in. I. D. permit sampling rates from
three to 20 cfm.
Filter; 11/2 in. diameter stainless cyclone
followed by a fabric filter. Filter require-
ments as per ASME Test Codes. While
the ASME suggested catch to filter weight
ratio of five to one is desirable, it would
not be practical for incinerator sampling
due to the low dust concentration and
therefore extended period of sampling
required.
Gas: Sampled gas volumes measured by cali-
brated pressure drop mechanism on
cyclone. Also measured by calibrated
orifice . . . per ASME Test Codes. Cor-
rection made for moisture content.
Vacuum: Clements - Cadillac G-10 blower
and exhaust fan. Per ASME Test Codes.
Velocity: Combined reverse inconel, pitot
tube. Per ASME Test Code traverse re-
quirements. Volumetric determination
not required as part of dustloading tests.
Advantages: 1) Reasonably reproducible re-
sults are obtainable with care. 2) Best
method encountered to secure reliable
quantitative results after considerable
experience with: a) WP-50 equipment.
b) Impingers, etc. 3} Test results rea-
sonably correlate with nuisance problems.
4) System variations in velocity do not
pose serious sampling problems.
Disadvantages: 1) Difficult and hazardous.
2) Tests are time consuming. 3) Average
results rather than instantaneous results
obtained. 4) Requires skilled personnel.
5) Requires quite expensive field and lab
equipment.
Incinerator: Domestic, comm., mun., flue
fed., spec.
Charges: All field tests made with material
on hand which is defined in the test re-
port. Some laboratory or controlled tests
run using ASA and other standardized
charges of our own. This work limited
to domestic and commerical incinerators.
Charging: All field tests made with material
on hand which is defined in the test report.
Some laboratory or controlled tests run
using ASA and other standardized charges
of our own. This work limited to domes-
tic and commercial incinerators.
^ir^Adj^ Continuous carbon dioxide
analysis with readings taken on a two to
three min cycle. Thermco CO9 electrical
conductivity analyzer used. Orsat analyses
run regularly to check continuous analyzer
and to get information on gas composition
molecular weight and density.
M_ethod: No quantitative odor tests reported
but odor observations made on all tests.
Analyses for noxious gases have included
aldehyde and ketone concentration of in-
cinerator effluents.
Ajr_gc^ution_Control District. Count
Los^Angeles. California. Carl V
JAPCA - Feb. 1957.
Code: Modification or extension of principles
and procedures outlined in WP-50 Bulletin.
Probe: Sampling probes of glass or stainless
steel. Nozzle sizes varied to be in the
isokinetic sample volume rate. Sampling
rate of 1/2 to one cfm makes nozzle size
range from 1/8 in. to 1/2 in. diameter.
One reference point in traverse used in
sampling. Several points necessary if
flow varies widely. Pitot tube used and
checked every five minutes at a fixed
point to adjust sampling rate.
Filter: Three Greenburg-Smith impingers
are used with a paper thimble usually.
For special purposes an alundum thimble
or a miniature glass cyclone can be used.
P.asJ A dry gas rneter is used. Correction
is made for moisture content. Meter is
of the Sprague 1A type.
Vacuum: A sampling pump is used.
Velocity: Standard or combined reverse
pitot tube used. Necessary to dustloading
test to make sample rate changes on five
minute interval.
Advantages: No comments included.
Disadvantages^ No comments included.
Incinerator^ Domestic, comm. mun. .flue fed.
spec.
13
-------
TestMgthgdgJor Determining Emission
Charges: For use in field tests. No stan-
dardization of charges for field tests
reported.
Charging: For use in field tests. No stan-
dardization of charge size or cycle for
field tests reported.
Excess Air Adi. : A sample of gas is collected
in a five liter bottle by acidified sodium sul-
fate displacement. An Orsat analysis is
run on the integrated gas sample. This
analysis used in excess air calculations.
Department of Air Pollution Control,City of
New York. M. M. Braverman, Director of
Laboratory (private communication)
Code^ Modification or extension of procedures
outlined in WP-50 Bulletin, ASME Test
Codes.
Prob!e.l Stainless steel probe. Fixed sample
location. Sampling rate periodically ad-
justed to isokinetic. Pitot tube used at
fixed point to indicate velocity variations.
Low rate sampling indicated - less than
one cfm.
Filter: Paper thimbles, cloth filters and
Greenburg-Smith impingers.
Gas: A dry gas meter.
.Vacuum: An air ejector or sampling pump.
Velocity: Standard pitot tube.
Advantages: Suggests that method involving
filter paper sampling would be simpler,
more automatic and less time consuming
than WP-50 technique. Suggests incorpor-
ating principles described in use of Von
Brand-Filtering Recorder as possible im-
proved standard.
Disadvantages: 1) Present methods are long,
tedious and cumbersome. 2) Suggests
that more investigative work is necessary
before standardized test procedures are
set up.
Incinerator: Domestic, comm., mun., flue
fed.
Charges: No information supplied or indicated
on standardized charges.
Charging: No information supplied or
indicated.
Air AdJ- - Periodic Orsat analysis.
Method: Threshold Dilution Method outlined
by ASTM Method D-1391.
|ai^I£a_A^r_Polk:tion_£ontrol District John
Yocom, Director of Technical Services
PAAPCD Booklet Test Methods.
Code: Modifications or extension of pro-
cedures outlined in WP-50 Bulletin.
-Probe: Short probes of glass, brass and
stainless steel - 3/16 in. to 1/2 in. I D
One point sampling in ducts less than'4 ft2
in velocities are reasonably uniform. Sam-
pling velocity adjusted by aid of one point
pitot tube reference or by pretest pitot
tube traverse.
Filter: Media incorporated in holder inside
stack or duct. Alundum and glass fibre
filter paper mentioned.
A Sprague 1A type dry gas meter.
.Vacuum: A sampling pump Of 1. 3 cfm
capacity or a Penberthy XL-96 ejector.
Velocity. A combined, reverse orStauscheibe
pitot tube.
Advantages: Eliminates problems caused by
condensation in the sampling train.
Disadvantages: Loss of particulates by com-
bustion or volatilization in filter holder
when used in stack.
Incinerator: Domestic, comm.
Charges: For use in field tests. No standardi-
zation of charges for field tests reported.
Charging: For use in field test. No stan-
dardization of charge size or cycle for
field tests reported.
Excess Air Adj.: Periodic Orsat analyses
are made and corrections made to a 6%
O2 basis.
Method: Suggests no detectable odor as a
standard using the nose as the instrument.
Also suggests tests show that below 50 ppm
carbonyls as formaldehyde have little
detectable odor.
14
-------
Test Methods for Determining Emission Characteristics of Incinerators
New York University College of Engineering,
Research Division, Elmer R. Kaiser, Senior
Research Scientists, JAPCA - Aug. 1959
(private communication)
Code: Modifications or extension of pro-
cedures outlined in WP-50 Bulletin and
per ASME Test Codes.
Probe: Western Precipitation stainless steel
sampling probe with 1/2 in. sharp-edged
nozzle. Sampling done at fixed locations.
Isokinetic sampling adjustment made by
use of Prandtl pitot tube. Sample rate
less than two cfm. Water-cooled probes
with 3/4 in. diameter nozzles were used on
special incinerator studies.
Filter: Paper thimbles and Greenburg-Smith
wet and dry impingers.
Gas: A Sprague 1A type dry gas meter. A
flowrator or rotameter was used to gauge
sampling velocity.
Vacuum: A central vacuum system.
Velocity: A Prandtl pitot tube of high tem-
perature alloy steel.
Advantages: 1) While probes were used at
fixed locations they could be used for
traversing. 2) The water-cooled probes
were necessary to prevent combustion of
carbonaceous particles in the probe. 3)
Impingers made good condensate-dust
catches.
Disadvantages: 1) The uncooled probe with
paper thimble was useful only in cool gas
with a dew point below ambient tempera-
ture. 2) Recommend an orifice meter
above two cfm. 3) Recommends null-type
probe rather than pitot tube and special
chart to secure isokinetic sampling.
Incinerator: Flue fed, spec.
Charges: For use in field tests. No standardi-
zation of charges for field tests reported.
Charging: For use in field tests. No stan-
dardization of charge size or cycle for
field tests reported.
Excess Air Adj.: Gas samples collected over
salt solution during test and analyzed for
CO2 and C>2 occasionally by Orsat analysis.
Method: The ASTM Method D1391-J957
Measurement of Odor in Atmosphere
(Dilution Method)" was used. Gas sampled
continuously into a one liter bottle con-
taining mercury. By mercury displace-
ment a composite sample was obtained.
The determination of threshold concen-
tration was made by one observer early
next morning. The ASTM odor method
using syringes is simple and inexpensive.
A plastic bag with aluminum foil liner
could be used instead of mercury for
sample procurement.
U.S. Public Health Service, R. A. Taft
Sanitary Engineering Center, Andrew H. Rose,
Jr., Chief, Engineering Research and Develop-
ment JAPCA - Feb. 1959.
Code: Modification or extension of procedures
outlined in ASME Test Codes.
Probe: Isokinetic sampling was conducted at
a fixed point in the laboratory studies.
Traversing was done on field municipal
incinerator studies. Isokinetic adjust-
ment was made by using pitot tube. A 1
in. I. D. sampling probe was used on the
laboratory tests.
Filter: MSA type 1106-BH glass-fiber filter
without organic binder.
Gas: Dry type bellows meter. A calibrated
orifice meter was used to control the in-
stantaneous sampling rate. Adjusted for
moisture content.
Vacuum: A vacuum pump.
Velocity: A standard pitot tube.
Advantages: No comments on sampling in-
cluded in paper.
Disadvantages: No comments on sampling
included in paper.
Incinerator: Comm., mun.
Charges: In laboratory tests, standardized
charges were used. A sack containing a
five Ib charge of fuel had a moisture con-
tent ranging from 23% to 27% consisted
of 1 1/2 Ib newspaper, 1 1/2 Ib of card-
board, one Ib wood and one Ib wet
vegetables.
15
-------
Test Methods for Determining Emission Characteristics of Incinerators
Charging: 10 and 15 Ib fuel charges were used
as were charging rates of 140 Ib/hr and
180 Ib/hr. Stoking interval was 10 min
and 20 min.
Excess Air Adj. : O2, CC>2 and CO continuous-
ly recorded in laboratory tests. Orsat
analyses used in field tests of municipal
incinerators. CO measured by MSA squeeze
bulb method at municipal incinerator.
Method: Odor observations were made and
reported as sufficiently low to be undetect-
able in the immediate vicinity of the stack.
Battelle Memorial Institute, Richard B.
Engdahl, Chief, Fuels and Air Pollution Re-
search. Report Project DG-3M. Report
Project DAG-4-M.
Code: American Standards Association, Inc.
Method with slight modification. Modified
ASME Test Codes followed in field tests
of Municipal incinerators.
Probe: 1 in. I. D. Pyrex glass sampling probe
in ASA test stack.
Filter: MSA type 1106B glass-fiber filter.
ASA method used plus a Greenburg-Smith
impinger was used in series with the filter.
Gas: ASA.
Vacuum: ASA.
Velocity: No determination.
Advantages: ASA modified for sampling over
entire period of burning rather than for a
15 min period as specified.
Disadvantages: ASA.
Incinerator: Domestic, mun.
Charges: ASA. Mixed refuse and shredded
paper charge.
Charging: ASA. Mixed refuse and shredded
paper charge size and cycle used.
Excess Air Adj.: A gas sample collected over
salt brine during test. Orsat analysis of
the average gas sample.
Method: ASA odor method with 50 ml glass
syringe, and two people used to make
observations and comparing results with
burning two sheets of newspaper in an
open container. A recent study indicated
16
that the CO concentration of domestic
gas-fired incinerators was a valid, ob-
jective indicator of odor intensity when
using ASA domestic waste charges.
Wisconsin Chemical & Testing Company,
Fred R. Rehm, Consultant (private
communication).
Code: Modified ASME Test Code for Deter-
mining the Dust Concentration in a Gas
Stream PTC 27-1957 and Test Code for
Dust-Separating Apparatus.
Probe: Balanced static tube method of iso-
kinetic sampling used. Stainless steel,
water-jacketed, probes and nozzles used -
3/4 in. to two in. I. D. Large sized sam-
ple rates three to 20 cfm considered
essential to secure representative sample.
Filter: 1 1/2 in. diameter, stainless cyclone
followed by fabric filter. Filter require-
ments as per ASME Test Codes, except
for five to one catch to bag weight ratio
which is impractical.
Gas: Calibrated orifices and calibrated pre-
sure drop mechanism as per ASME Test
Codes.
Vacuum: Clements - Cadillac G-10 blowers
and exhausters.
Velocity: Combined reverse, inconel, pitot
tube and standard pitot for clean gases, as
per ASME Test Codes.
Advantages: See No. 8, above.
Disadvantages: See No. 8, above.
Incinerator: Domestic, comm.,mun., flue
fed., spec.
Charges: Standardized charges used on some
lab tests consisting of: (25% HgO max)
54. 2% paper, 36. 9% wood boxes, 8. 9%
rubber foot pads. No standardization on
field tests.
Charging: Charging on five minute cycles.
No standardization on field tests.
Excess Air Adj.: Continuous CO2- Analysis
checked regularly by Orsat analysis.
Method: Odor observations made on alltests.
Analysis of incinerator gases forcarbonyl
content made and degree of correlation to
odor levels attempted.
-------
J^gLMethodsforDeterniining Emission
Bureau of Air Pollution Control, City of
Detroit, Morton Sterling, Director, Robert
S. Bower. Sr., Assistant Mechanical Engi-
neer (private communication) JAPCA -
Aug. 1961.
Code: Modified ASME PTC 21-1941 Modified
Probej ASA.
Filter: ASA.
Gas: ASA.
Vacuum: High volume pump.
Velocity: Velometer.
Advantages: 0 ASME PTC-21 acceptable
method for particulate testing. 2) ASA-
Z 21.G 1957 probably satisfactory for lab
testing. 3) Smoke emissions need not be
measured at all if restrictive and accurate
particulate and odor tests are conducted.
Disadvantages: 1) Tests are time consuming
and costly.
Incinerator: Domestic.
Charges^ There is a need for a standard test
charge, but the components should be of a
more rigorous and representative nature
than the present innocuous ASA food charge.
Items like coffee grounds, carpet sweep-
ings, plastic wrappers, damp cotton should
be included. ASA and three other standar-
dized charges used.
Charging: ASA.
Excess_Air_Adj. : Integrated gas samples
taken at a constant rate by liquid displace-
ment during the particulate sampling
period. Orast analyses run on the in-
tegrated gas sample for excess air
adjustment.
Method: A special odor panel technique using
five members compare odors in a special
room with that from two burning sheets of
newspaper in an open container. The odor
is assessed at one minute intervals. A 15
to one air to gas dilution ratio was used.
While the technique used was imperfect
in some respects, it proved fairly satis-
factory. Odor tests were found the most
difficult for incinerators to pass. Feels
that adequate odor measurement technique
alone may be sufficient measure of per-
formance evaluation of domestic incinerators.
Performance Evaluation Sub-Committee:
Fred R. Rehm, Chairman
Leo P. Flood
Elmer R. Kaiser
Andrew H. Rose, Jr.
John R. Sved
REFERENCE
1 Rehm, F. R. Test Methods for Determining
Emission Characteristics of Incinerators
J. A. P. C.A. Vol. 15, No. 3, pp 127-35.
March 1965.
17
-------
Section 10
REFERENCE MATERIALS
Conversion Factors and Tables
-------
CONVERSION FACTORS
Page
TEMPERATURE 2
PRESSURE 3
AREA 4
VOLUME 5
FLOW 6
WEIGHT 7
CONCENTRATION 8
LENGTH 9
EMISSION RATES 10
VELOCITY 11
LOGARITHMS
10-54 to Base 10 12
55-99 to Base 10 13
-------
CONVERSION FACTORS - TEMPERATURE
cn
•tH
c
•l-l
o
Degrees
Fahrenheit
Degrees
Centigrade
Degrees
Rankin
Degrees
Kelvin
Desired Units
°F
1. 8°C + 32
°R - 460
1. 8(°K-273) + 32
°C
. 5555 x
(°F - 32)
. 5555 x
(°R - 492)
°K - 273
°R
°F + 460
1. 8°C + 492
1. 8(°K-273) + 492
°K
. 5555 x
(°F-32) + 273
°C + 273
. 5555 x
(°R-492) + 273
-------
CONVERSION FACTORS - PRESSURE
^>ss^ units
Given ^**»w^
units ^^S(^
6mm
cm-sec2
dynes
cm^
#m
ft-sec2
poundals
ft^
gmf
cm*
»t
•t
in-2
"Atmospheres"
6mm
9
cm-sec'
1
1
14. 882
14.882
980. 665
478. 80
6.8948
X 104
1. 0133
X 106
dynes
cm2
1
1
14. 882
14. 882
980. 665
78. 80
6. 8948
X 104
1.0133
X 106
*m
ft-sec2
6. 7197
X ID"2
6. 7197
X 10-2
1
1
65. 898
32. 174
4. 6331
X 103
6. 8087
X 104
poundals
ft2
6. 7197
X 10'2
6. 7197
X 10-2
1
1
65. 898
32. 174
4. 6331
X 103
6. 8087
X 104
gmf
cm2
1. 0197
X ID"3
1. 0197
X 10"3
1. 5175
X lO"2
1. 5175
X 10"2
1
4.8824
X 10'1
70. 307
1.0332
X 103
™«~^^™^
*f
ft2
2. 0885
X 10'3
2. 0885
X 1C'3
3. 1081
X 10~2
3. 1081
X 10'2
2. 0482
1
144. 00
2. 1162
X 103
^^^•••MU^B
*f
in2
1. 4504
X 10"5
1. 4504
X 10'5
2. 1584
X 10'4
2. 1584
X 10'4
1.4223
X 10'2
6. 9444
X 10'3
1
14. 696
•i^— «^-^_i
"Atmospheres"
9. 8692
X 10"7
9. 8692
X 10'7
1. 4687
X 10~5
1. 4687
X 10-5
9. 6784
X 10'4
4. 7254
X 10'4
6. 8046
X 10"2
1
•^M^^^^^^HM^^^
^^"^de'sSuniir" UnU l° 3 dCSired Unlt' mUUlply te giVe" ValUe b* «» fact- °PP-ite th. given units
-------
CONVERSION FACTORS - AREA
Given Units
Square
Inch
Square
Foot
Square
Yard
Square
Mile
Acre
Square
Centimetei
Square
Decimeter
Square
Meter
Square
Kilometer
Desired Units
Square
Inch
1
144
1296
40. 144
x 108
62. 73
x 107
15. 5x10-2
15. 5
15. 5 x 10Z
15. 5 x 108
Square
Feet
6. 9444
x 10~3
1
9
2. 788
x 107
4. 3560
x 104
10. 764
x ID'4
10. 764
x 10~2
10. 764
10. 764
x 1C6
Square
Yard
77. 1605
x lO-5
0. 1111
1
3. 098
x 106
4840
1. I960
x lO'4
1. I960
x ID"2
1.1960
1. 1960
x 106
Square
Mile
2. 49
x 10-1°
3. 587
x 10~8
3. 228
x 10"7
1
15. 625
x lO'4
3. 8610
x 10'11
3. 8610
x 10-9
3.8610
x 10-7
3. 8610
x 10-1
Acre
15. 94
x ID"6
2. 296
x 10'5
2. 066
x 1C'4
640
1
2. 471
x ID"8
2. 471
x 10-6
2. 471
x ID"4
2. 471
x 102
Square
Centimeter
6. 452
929. 0341
83.61
x 102
2. 589998
x IQlO
4046. 873
x 104
1
1 x 102
1 x 104
1 x 1010
Square
Decimeter
6. 452
x 10~2
929. 0341
x 10~2
83. 61
2. 589998
x 108
4046. 873
x 102
1 x 10-2
1
Lx 102
1 x 10b
Square
Meter
6. 452
x ID'4
929. 0341
x 10-4
83. 61
x 10'2
2. 589998
x 106
4046. 873
1 x 10~4
1 x 10-2
1
1 x 106
Square
Kilmeter
6.452
x 10-10
929. 0341
x 10-1°
83. 61
x 10-8
2.589998
4046. 873
x 10~6
1 x 10-1°
1 x 10-8
1 x lO"6
1
To convert a value from a given unit a desired unit, multiply the given value by the factor opposite the given units
and beneath the desired unit.
-------
CONVERSION FACTORS - VOLUME
^^^Desired
G ive n^^^Units
Units ^^<^
Cubic
Yard
Cubic
Foot
Cubic
Inch
Cubic
Meter
Cubic
Decimeter
Cubic
Centimeter
Liter
Cubic
Yard
1
3.7037
x io"2
2. 143347
x io"5
1.30794
1.3079
x io"3
1.3079
x io~6
1.3080
x io"3
Cubic
Foot
27
1
5.78704
x io"4
35.314445
3.5314
x io"2
3. 5314
x io"5
3. 5316
x io"2
Cubic
Inch
4.6656
x io4
1728
1
6. 1023
x io4
61.023
6. 1023
x io"2
61.025
Cubic
Meter
0.764559
2. 8317
x io"2
1.63872
x io"5
1
0.001
i x io'6
1.000027
x io"3
Cubic
Decimeter
764.559
28. 317
1.63872
x io"2
1000
1
1 X IO"3
1.000027
Cubic
Centimeter
7.64559
x io5
2.8317
X IO4
16.3872
1 X IO6
1000
1
1000.027
Liter
764. 54
28.316
1.63868
x io"2
999.973
.99997
9.99973
x io"4
1
To convert a value from a given unit to a desired unit, multiply the given value by the factor opposite the given units
and beneath the desired units.
-------
CONVERSION FACTORS - FLOW
^SJJnits
Given ^^^^
Units ^^^
sec
min
hour
sec
min
hour
sec
min
sec
min
sec
1
0.0167
x to"5
x io"3
x io~4
X 10'6
x io"3
X 10"S
1 X 10'6
xio-"
M
mm
60
1
X IO"3
1.699
X IO"3
X IO"4
X 10"2
X IO"3
6 X Ifl'5
1 X 10'6
M3
hour
3600
60
1
101.94
1.699
x io"3
3.6
x io"2
3.6 X 10~3
6 X io"5
ft3
sec
35.3144
0.5886
98.90
1
16.667
x,o-3
x io"4
35.316
5.886
xio-4
3. 5314
x io"5
5.886
x io"7
ft3
mm
21. 1887
35.3144
0.5886
60
1
16.667
2. 11896
35.316
2. 1189
0.3531
x io"4
f,3
hour
12.7132
x,o4
21. 189
xio2
35.3144
3600
60
1
127. 138
2. 11896
1.271
x io"3
2. 1 1887
X IO"3
L
sec
999.973
16.667
27. 777
x io"2
28.316
47. 193
x io"2
7.866
X10-3
1
1.6667
x,o-2
9.99973
xio-4
5.9998
x io~2
L
min
59.998
3
999.973
16.667
16.9896
X IO2
28.316
0.4719
60
1
5.9998
X IO"2
9.99973
x io"3
cm3
sec
1 X IO6
16.667
X IO3
2.777
2
2.8317
X IO4
4.7195
78.658
1000.027
16.667
1
16.667
x 10-3
10 convert a value from a g.ven Un,t to a desired unit, multiply the given value by the factor opposite the given units and beneath the desired unit.
1 3 1
min
6 X IO7
IX IO6
1.666
1.699
2.8317
4.7195
2
16.667
1000.027
60
I
-------
CONVERSION FACTORS-WEIGHT
Given Units
Micro-
gram
Milli-
gram
gram
Kilogram
grain
Ounce
(avdp)
Pound
(avdp)
Ton
(U.S. shoi
Tonne
(metric)
Desired Units
Micro-
gram
1
1 x 103
1 x 10b
1 x 109
64. 799
x 103
28. 349
x 106
453. 59
x 10b
905. 185
•t) x 109
1 x 1012
Milli-
gram
1 x lO'^
1
1 x 103
1 x 10b
64. 799
28. 349
x 103
453.59
X 103
907.185
x 106
1 x 109
gram
1 x 10"b
1 x lO"3
1
1 x 103
64. 799
x ID"3
28. 349
453. 59
907. 185
x 103
1 x 10fa
Kilo-
gram
1 x 10-9
1 x ID'6
1 x 10'3
1
64.799
x lO'6
28. 349
x 10'3
453. 59
x lO"3
907.185
1 x 103
grain
15.4124
x 10'6
15. 4324
x 10'3
15. 4324
15. 4324
x 103
1
437. 5
7000
14 x 106
1. 543 xlO'
Ounce
(avdp)
3. 5274
x ID'8
3. 5274
x ID"5
3. 5274
x lO-2
35. 274
22.857
x ID'4
1
16
3. 2
x 104
' 3.5274
x 104
Pound
(avdp)
2. 2046
x 10-9
2. 2046
x 10-6
2. 2046
x 10'3
2. 2046
1. 4286
x ID"4
62. 5
x 10~3
1
2000
2204. 62
Ton
(U.S. short
1.1023
x 10~12
1.1023
x 10-9
1.1023
x lO-6
1.1023
x 10~3
7. 143
x 10~8
3. 125
x ID"5
5 x ID'4
1
1.10231
Tonne
;) (metric)
1 x ID'12
1 x 10-9
1 x 10-6
1 x ID"3
64. 799
x 10-9
28. 349
x lO-6
453. 59
x 10-6
0. 907185
1
-------
CONVERSION FACTORS - CONCENTRATION
l/>
4->
•H
C
=>
C
• H
u
_££_
M3
-£&.
M3
_ifg.
L
oz
ft. 3
Ibs.
ftT3"
grams
ft.3
Ibs.
1000 ft. 3
grains
ftT3"
M£
M^
1
1 x 1C-3
.999973
1. 00115
x 106
1.602
x 10?
3. 531
x 104
1. 602
x 104
2. 288
x 103
Desired Units
-*$-
M3
1000
1
9. 99973
x 102
1. 00115
x 109
1.602
x 1010
3. 531
x 107
1.602
x 107
2. 288
x 106
_/iS_
L
1. 000027
1. 000027
x 10-3
1
1.00118
x 106
1.602
x 10?
3.531
x 104
1. 602
x 104
2. 288
x 103
oz
fT3
9. 989
x 10-7
9. 989
x lO-iO
9. 988
x 10'7
1
16
3. 5274
x 10-2
1.6
x 10'2
2. 2857
x 10-3
Ibs.
ft. J
6. 243
x 10-8
6. 243
x 10-11
6. 242
x 10-8
62.5
x 10'3
1
2. 20462
x 10-3
1 x 10'3
1.4286
x ID'4
grams
ftT^
2.8317
x 10-5
2.8317
x 10~8
2.8316
x lO-5
28.349
453. 59
1
453. 59
x 10-3
6.4799
x 10-2
Ibs.
1000 ft. 3
6. 243
x 1C-5
6.243
x 10-8
6. 242
x 10-5
62. 5
1 x 103
2. 2046
1
14. 286
grains
ftT3
4. 37
x ID'4
4.37
x 10-7
4. 37
x 10-4
4.375
x 102
7 x 103
15.43
7
1
-------
CONVERSION FACTORS - LENGTH
^^J)esired
... ^*^UnHs
Given ^^.
Units ^N,.
Inch
Foot
Yard
Mile
Micron
Millimeter
Centimeter
Meter
Kilometer
Inch
1
12
36
6.3360
x io4
3.937
X IO"5
3.937
x io"2
3.937
x io"1
39.37
3.937
x io4
Foot
83. 33
x io"3
1
3
5280
32.808
x io"7
32.808
x io"4
32.808
x io"3
32.808
x io"1
32.808
x io2
Yard
27.778
x io"3
3333
1
1760
10.94
x io"7
10.94
x io"4
10.94
x io"3
10.94
x io"1
10.94
X IO2
Mile
1.578
x io"5
1.894
x io"4
5.682
x io"4
1
62. 137
xio-11
62. 137
X 10~8
62. 137
x io"7
62. 137
x io"5
62. 137
x io"2
Micron
2.54
x io4
30.48
x io4
91.44
X IO4
1.6094
X IO9
1
1 X IO3
1 X IO4
i x io6
1 X IO9
Millimeter
25.4
304.8
914. 4
1.6094
X IO6
1 X io"3
1
10
1 X IO3
ix io6
Centimete
2.54
30.48
91.44
1.6094
x,o5
i x ,o-4
0. 1
1
i x io2
ix io5
Meter
2.54
x io"2
30.48
x io~2
91.44
X io"2
1. 6094
IX l
1 X IO3
Kilometer
2. 54
x io"5
30.48
x io"5
91.44
xio-5
1.6094
IX 10'9
1 X 10~6
1 X lo"5
i x io'3
'
To convert a value from a given unit to a desired unit, multiply the given value by the factor opposite the given units and beneath the desired units.
-------
CONVERSION FACTORS - EMISSION RATES
^^^^ units
Given ^^«^^
units ^"^V^
gms/sec
gms/min
kg/hr
kg/day
Ibs/ mln
Ibs/hr
Ibs /day
tons/hr
tons /day
tons/yr
gms/sec
1.0
1. 6667
X 10-2
2. 7778
X 10"1
1. 1574
X ID'2
7. 5598
1. 2600
x 10- l
5. 2499
X 10"3
2.5199
X 102
1.0500
X 10
2.8766
X ID'2
gms/ min
60.0
1.0
16. 667
6. 9444
X 10"1
4. 5359
X 102
7. 5598
3. 1499
X 10-1
1.5120
X 104
6. 2999
X 102
1.7260
kg/hr
3.6
6.0
X 10-2
1.0
4. 1667
X ID'2
2. 7215
X 10
4. 5359
x 10-1
1. 8900
X ID'2
9. 0718
X 102
3. 7799
X 10
1. 0356
X lO"1
kg/ day
8. 640
X 10
1.4400
2.4000
X 10
1.0
6.5317
X 102
1.0886
X 10
4.5359
X ID'1
2. 1772
X 104
9. 0718
X 102
2.4854
Ibs/ min
1.3228
X ID'1
2. 2046
X 10-3
3.6744
X 10-2
1.5310
X 10-3
1.0
1. 6667
X ID'2
6. 9444
X 10'4
3. 3333
X 10
1. 3889
3. 8052
X 10-3
Ibs/hr
7. 9367
1. 3228
X 10'1
2. 2046
9. 1860
X ID'2
60. 0
1.0
4. 1667
X 10-2
2.0
X 103
8. 3333
X 10
2. 2831
X 10'1
Ibs /day
1.9048
X 102
3. 1747
5. 2911
X 10
2.2046
1.44
X 103
24.0
1. 0
4. 8000
X 104
2.0
X 103
5.4795
tona/hr
3. 9683
X 10'3
6.6139
X 10'5
1. 1023
X 10-3
4. 5930
X 10"5
3.000
X ID'2
5. 0000
X 10"4
2. 0833
X 10"5
1.0
4. 1667
X 10'2
1. 1416
X 10"4
tons/ day
9.5240
X 10'2
1. 5873
X 10"3
2. 6456
X 10-2
1. 1023
X 10-3
7. 2000
X 10'1
1. 2000
X 10-2
5. 0000
X 10'4
4.0
1.0
2. 7397
X 10-3
tons/yr
3.4763
X 10
5.7938
X 10'1
9. 6563
4.0235
X 10"1
2. 6280
X 102
4. 3800
1. 8250
x 10-1
8. 7600
X 103
65. 0
1. 0
To convert a value from a given unit to a desired unit, multiply the given value by the factor opposite the given units and beneath
the desired units.
-------
CONVERSION FACTORS - VELOCITY
"^^^ Desired
^*^x^ units
Given ^^^^
units ^^"^
m/ sec
ft/ sec
ft/min
km/hr
mi/hr
knots
mi/day
ml sec
1. 0
3. 0480
X 10'1
5.0080
X 10"3
2. 7778
X 10"1
4.4707
X 10'1
5. 1479
X ID'1
1. 8627
X ID"2
ft/ sec
3. 2808
1.0
1. 6667
X 10-2
9. 1134
X 10'1
1.4667
1. 6890
6. 1111
X lO'2
ft/min
1. 9685
X 102
60
1. 0
5.4681
X 10
88.0
1. 0134
X 102
Si 6667
km/hr
3. 6
1. 0973
1. 8288
X 10"2
1. 0
1. 6093
1, 8533
6. 7056
X 10'2
mi/hr
2. 2369
6. 8182
X 10'1
1. 1364
X 10~2
6. 2137
X 10'1
1.0
1. 1516
4. 1667
X 10-2
knots
1. 9425
5. 9209
X 10'1
9. 8681
X 10"3
5. 3959
X 10' l
8. 6839
X lO"1
1. 0
3. 6183
X ID'2
mi/day
5. 3687
X 10
1. 6364
X 10
2. 7273
X lO'1
1.4913
X 10
24
2. 7637
X 10
1. 0
To convert a
opposite the
value from a given unit
given units and beneath
to a desired unit, multiply the given value by the factor
the desired units.
-------
LOGARITHMS TO BASE 10
N
!•
11
12
13
14
15
16
17
18
19
2»
21
22
23
.24
25
26
27
28
29
M
31
32
33
34
35
36
37
38
39
M
41
42
43
44
45
40
47
48
49
M
51
52
53
54
N
01234
0000 0043 0086 0128 0170
0414 0453 0492 0531 0569
0792 0828 0864 0899 0934
1139 1173 1206 1239 1271
1461 1492 1523 1553 1584
1761 1790 1818 1847 1875
2041 2068 2095 2122 2148
2304 2330 2355 2380 2405
2553 2577 2601 2625 2648
2788 2810 2833 2856 2878
3010 3032 3054 3075 3096
3222 3243 3263 3284 3304
3424 3444 3464 3483 3502
3617 3636 3655 3674 3692
3802 3820 3838 3856 3874
3979 3997 4014 4031 4048
4150 4166 4183 4200 4216
4314 4330 4346 4362 4378
4472 4487 4502 4518 4533
4624 4639 4654 4669 4683
4771 4786 4800 4814 4829
4914 4928 4942 4955 4969
5051 5065 5079 5092 5105
5185 5198 5211 5224 5237
5315 5328 5340 5353 5366
5441 5453 5465 5478 5490
5563 5575 5587 5599 5611
5682 5694 5705 5717 5729
5798 5809 5821 5832 5843
5911 5922 5933 5944 5955
6021 6031 6042 6053 6064
6128 6138 6149 6160 6170
6232 6243 6253 6263 6274
6335 6345 6355 6365 6375
6435 6444 6454 6464 6474
6532 6542 6551 6561 6571
6628 6637 6646 6656 6665
6721 6730 6739 6749 6758
6812 6821 6830 6839 6848
6902 6911 6920 6028 6937
6990 8998 7007 7016 7024
7076 7084 7093 7101 7110
7160 7168 7177 7185 7193
7243 7251 7259 7267 7275
7324 7332 7340 7348 7356
01234
56789
0212 0253 0294 0334 0374
0607 0645 0682 0719 0755
0969 1004 1038 1072 1106
1303 1335 1367 1399 1430
1614 1644 1673 IV 03 1732
1903 1931 1959 1987 2014
2175 2201 2227 2253 2279
2430 2455 2480 2504 2529
2672 2695 2718 2742 2765
2900 2923 2945 2967 2989
3118 3139 3160 3181 3201
3324 3345 3365 3385 3404
3522 3541 3560 3579 3598
3711 3729 3747 3766 3784
3892 3909 3927 3945 3962
4065 4082 4099 4116 4133
4232 4249 4265 4281 4298
4393 4409 4425 4440 4456
4548 4564 4579 4594 4609
4698 4713 4728 4742 4757
4843 4857 4871 4886 4900
4983 4997 5011 5024 5038
5119 5132 5145 5159 5172
5250 5263 5276 5289 5302
5378 5391 5403 5416 5428
5502 5514 5527 5539 5551
5623 5035 5647 5658 5670
5740 5752 5763 5775 5786
5855 5866 5877 5888 5899
5966 5977 5988 5999 6010
6075 6085 6096 6107 6fl7
6180 6191 6201 6212 6222
6284 6294 6304 6314 6325
6385 6395 6405 6415 6425
6484 6493 6503 6513 6522
6580 6590 6590 6609 6618
6675 6684 6693 6702 6712
6767 6776 6785 6794 6803
6857 6866 6875 6884 6893
6946 6955 6964 6972 6981
7033 7042 7050 7059 7067
7118 7126 7135 7143 7152
7202 7210 7218 7226 7235
7284 7292 7300 7308 7316
7364 7372 7380 7388 7396
56789
Proportional Ptrto
123456789
4 8 12 17 21 25 29 33 37
4 8 11 15 19 23 26 30 34
3 7 10 14 17 21 24 28 31
3 6 10 13 16 19 23 26 29
3 6 9 12 15 18 21 24 27
3 6 8 11 14 17 20 22 25
3 5 8 11 13 16 18 21 24
2 5 7 10 12 15 17 20 22
2 5 7 9 12 14 16 19 21
2 4 7 9 11 13 16 18 20
2 4 6 8 11 13 15 17 19
2 4 6 8 10 12 14 16 18
2 4 6 8 10 12 14 15 17
2 4 6 7 9 11 13 16 17
2 4 5 7 9 11 12 14 16
2 3 5 7 9 10 12 14 19
2 3 5 7 8 10 11 13 15
2 3 5 6 8 9 11 13 14
2 3 5 6 8 9 11 12 14
1 3 4 6 7 9 10 12 13
1 3 4 6 7 9 10 11 13
1 3 4 6 7 8 10 11 12
1 3 4 5 7 8 9 11 12
1 3 4 5 8 8 9 10 12
1 3 4 5 6 8 9 10 11
1 2 4 5 6 7 9 10 11
1 2 4 5 6 7 8 10 11
12356789 10
12356789 10
12345789 10
1 2345689 10
123456789
123456789
123456789
123456789
123456789
123456778
123455678
123445678
123446678
123345678
123345678
122345677
122345667
122345667
123456789
The proportional parts are stated in full for every tenth at the right-hand side.
The logarithm of any number of four significant figures can be read directly by
adding the proportional part corresponding to the fourth figure to the tabular
number corresponding to the first'three figures. There may be an error of 1 in
tht- last place.
-------
LOGARITHMS TO BASE 10
(continued)
N
65
56
57
58
59
M
61
62
63
64
65
66
67
68
69
7»
71
72
73
74
75
76
77
78
79
M
81
82
83
84
85
86
87
88
89
M
91
92
93
94
95
96
97
98
99
N
01234
7404 7412 7419 7427 7435
7482 7490 7497 7505 7513
7559 7566 7574 7582 7589
7634 7042 7649 7657 7664
7709 7710 7723 7731 7738
7782 7789 7796 7803 7810
7853 7860 7868 7875 7882
7924 7931 7938 7945 7952
7993 8000 8007 8014 8021
8062 8069 8075 8082 8089
8129 8136 8142 8149 8156
8195 8202 8209 8215 8222
8261 8267 8274 8280 8287
8325 8331 8338 8344 8351
8388 8395 8401 8407 8414
8451 8457 8463 8470 8476
8513 8519 8525 8531 8537
8573 8579 8585 8591 8597
8633 8639 8645 8651 8657
8692 8698 8704 8710 8716
8751 8756 8762 8768 8774
8808 8814 8820 8825 8831
8865 8871 8876 8882 8887
8921 8927 8932 8938 8943
8976 8982 8987 8993 8998
9031 9036 9042 9047 9053
9085 9090 9096 9101 9106
9138 9143 9149 9154 9159
9191 9196 9201 9206 9212
9243 9248 9253 9258 9263
9294 9299 9304 9309 9315
9345 9350 9355 9360 9365
9395 9400 9405 9410 9415
9445 9450 9455 9460 9465
9494 9499 9504 9509 9513
9542 9547 9552 9557 9562
9590 9595 9600 9605 9609
9638 9643 9647 9652 9657
9685 9689 9694 9699 9703
9731 9736 9741 9745 9750
9777 9782 9786 9791 9795
9823 9827 9832 9836 9841
9868 9872 9877 9881 9886
9912 9917 9921 9926 9930
9956 9961 9965 9969 9974
01234
5 6 7 8 9
7443 7451 7459 7466 7474
7520 7528 7536 7543 7551
7597 7604 7612 7619 7627
7672 7679 7686 7694 7701
7745 7752 7760 7767 7774
7818 7825 7832 7839 7846
7889 7896 7903 7910 7917
7959 7966 7973 7980 7987
8028 8035 8041 8048 8055
8096 8102 8109 8116 8122
8162 8169 8176 8182 8189
8228 8235 8241 8248 8254
8293 8299 8306 8312 8319
8357 8363 8370 8376 8382
8420 8426 8432 8439 8445
8482 8488 8494 8500 8506
8543 8549 8555 8561 8567
8603 8609 8615 8621 8627
8663 8669 8675 8681 8686
8722 8727 8733 8739 8745
8779 8785 8791 8797 8802
8837 8842 8848 8854 8859
8893 8899 8904 8910 8915
8949 8954 8960 8965 8971
9004 9009 9015 9020 9025
9058 9063 9069 9074 9079
9112 9117 9122 9128 9133
9165 9170 9175 9180 9186
9217 9222 9227 9232 9238
9269 9274 9279 9284 9289
9320 9325 9330 9335 9340
9370 9375 9380 9385 9390
9420 9425 9430 9435 9440
9469 9474 9479 9484 9489
9518 9523 9528 9533 9538
9566 9571 9576 9581 9586
9614 9619 9624 9628 9633
9661 9666 9671 9675 9680
9708 9713 9717 9722 9727
9754 9759 9763 9768 9773
9800 9805 9809 9814 9818
9845 9850 9854 9859 9863
9890 9894 9899 9903 9908
9934 9939 9943 9948 9952
9978 9983 9987 9991 9996
56789
Proportional Parts
123456780
122345567
122345567
122345567
1 12344567
1 12344567
1 12344566
1 12344660
1 12334566
112334656
112334666
112334556
112334556
112334556
112334456
112234456
112234456
112234455
112234455
1 12234455
112234456
1 12233455
112233455
112233 45
112233 45
112233 45
112233 45
112233 45
112233 45
112233445
112233445
112233445
1 12233445
011223344
011223344
011223344
011223344
011223344
011223344
01122334
01122334
01122334
01122334
01122334
01122334
011223334
123456789
T'nc proportional parts are stated in full for every tenth at the right-hand side.
The logarithm of any number of four significant figures can be read directly by
adding the proportional part corresponding to the fourth figure to the tabular
number corresponding to the first three figures. There may be an error of 1 in
the last place.
13
-------
INTERNATIONAL ATOMIC WEIGHTS
BASED ON CARBON - 12
Actinium
Aluminum
Americium
Antimony
Argon
Arsenic
Astatine
Barium
Bcrkclium
Beryllium
3ismuth
Boron
Bromine
Cadmium
Calcium
Californium
Carbon
Cerium
Cesium
Chlorine
Chromium
Cobalt
Copper
Curium
Dysprosium
Einsteinium
Erbium
Europium
Fermium
Fluorine
Francium
Gadolinium
Gallium
Germanium
Gold
Hafnium
Helium
Holmium
Hydrogen
Indium
Iodine
Iridium
Iron
Krypton
Lanthanum
Lead
Lithium
Lutetium
Magnesium
Manganese
Mendelevium
6ym*
bol
Ac
Al
Am
Sb
Ar
A3
At
Ba
Bk
Be
Bi
B
Br
Cd
Ca
Cf
c
Ce
Cs
Cl
Cr
Co
Cu
Cm
Dy
Es
Er
Eu
Fm
F
Fr
Gd
Ga
Ge
Au
Hf
He
Ho
H
In
I
Ir
Fe
Kr
La
Pb
Li
Lu
Mg
Mn
Md
Atomic
Number
89
13
ys
51
18
33
85
56
97
4
83
5
35
48
20
98
6
68
55
17
24
27
29
96
66
99
68
63
100
9
87
64
31
32
79
72
2
67
1
49
53
77
26
30
57
82
3
71
12
25
101
Atomic
Weight
[227] *
20.9815
I243J *
J21.75
39.948
74.9216
|210]*
137.34
[249] *
9.0122
20S.9SO
10.811 °
79.909 *
112.40
40.08
[251|*
12.01115a
140.12
132.905
35.453 fc
51.996"
58.9332
63.54
[247]*
1C2.50
1254]*
167.26
151.96
[253] *
18.9984
[223] *
157.25
69.72
72.59
196.967
178.49
4.0026
164.930
1.00797°
114.82
126.9044
192.2
55.847 6
83.80
138.91
207.19
G.939
174.97
24.312
54.9380
[256] *
Mercury
Molybdi-uum
Neodymium
Neon
Neptunium
Nickel
Niobium
Nitrogen
Nobelium
Osmium
Oxygen.
Palladium
Phosphorus
Platinum
Plutonium
Polonium
Potassium
Praseodymium
Promethium
Protactinium
Radium
Radon
Rhenium
Rhodium
Rubidium
Ruthenium
Samarium
Scandium
Selenium
Silicon
Silver
Sodium
Strontium
Sulfur
Tantalum
Technetium
Tellurium
Terbium
Thallium
Thorium
Thulium
Tin
Titanium
Tungsten
Uranium
Vanadium
Xenon
Ytterbium
Yttrium
Zinc
Zirconium
Sym-
bol
H?
Mo
Nd
Ne
Sp
Ni
Nb
N
No
Qs
0
Pd
P
Pt
Pu
Po
K
Pr
Pm
Pa
Ra
Rn
Re
Rh
Rb
Ru
Sm
Sc
Se
Si
Ag
Na
Sr
S
. Ta
Tc
Te
Tb
Tl
Th
Tm
Sn
Ti
W
U
V
•Xc
Yb
Y
Zn
Zr.
Atomic
Number
Atomic
Weight
80 200.59
42 95.94
60 144.24
10 20.183
93 [237] *
28
41
7
58.71
92.906
14.0067
102 254] *
76
8
46
15
78
190.2
15.9994 -
10ti.4
30.9738
195.09
94 |242] *
84 [210] *
19
59
39.102
140.907
61 1147|*
91
88
86
75
45
37
44
02
21
34
14
47
11
38
16
73
43
52
65
81
90
69
50
22
74
92
23
54
70
39
30
40
231 •
226 *
222 *
186.2
102.905
85.47
101.07
150.35
44.950
78.96
28.086 "
107.870 »
22.9S9S
87.62
32.064 *
180.948
|99|*
127.60
158.924
204.37
232.038
168.934
118.69
47.90
183.85
238.03
50.942
131.30
173.04
88.905
65.37
91.22
• Value In bracket! denotes the mass number of tbe Isotope of longest known half life (or a better known one
tor Bk. Cf. Po. Pm. and Tc).
'Atomic welgbt varies because of natural variation In Igotoplc composition: B. ±0.003; C. ±0.00005.
H. ±0.00001 ;O, ±0.0001:31, ±0.001; S, ±0.003.
4 Atomic weight Is believed to have follo-ving experimental uncertainty: Br. ±0.002: Cl. ±0.001; Cr. ±0.001;
Fe, ±0.003; AII, ±0.003. For other dementi, the last digit Riven for tbe atom): weight la believed reliable to
±0.5. I.awreoclum. Lw. has been proposed aa the Damp lor .-Icintnt No. 103, nucllJlc mass about 267.
-------
VAPOR PRESSURES OF WATER AT SATURATION
(inches of Mercury)
Temp.
Deg. F.
20
10
~"r
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
250
260
270
280
290
300
310
320
330
340
350
360
370
380
390
400
0
.0126
.0222
.0376
.0376
.0631
.1025
.1647
.2478
.3626
.5218
.7392
1.032
1.422
1.932
2.596
3.446
4.525
5.881
7.569
9.652
12.20
15.29
10.01
23.47
28.75
35.00
42.31
50.84
60.72
72.13
85.22
100.2
117.2
136.4
158.2
182.6
209.8
240.3
274.1
311.6
353.0
398.6
448.6
503.6
1
.0119
.0209
.0359
.0398
.0660
.1080
.1716
.2576
.3764
.5407
.7648
1.066
1.467
1.992
2.672
3.543
4.647
6.034
7.759
9.885
12.48
15.63
19.42
23.96
29.33
35.68
43.11
51.76
61.79
74.36
86.63
101.8
119.0
138.5
160.5
185.2
212.7
243.5
277.7
315.5
357.4
403.4
453.9
509.3
2
.0112
.0199
.0339
.0417
.0696
.1127
.1803
.2677
.3906
.5601
.7912
1.102
1.513
2.052
2.749
3.642
4. 772
6.190
7.952
10.12
12.77
15.98
19.84
24.46
29.92
36.37
43.92
52.70
62.88
74.61
88.06
103.4
120.8
140.6
162.8
187.8
215.6
246.8
281.3
319.5
361.8
408.2
459.2
515.1
3
.0106
.0187
.0324
.0463
.0728
.1186
.1878
.2782
.4052
.5802
.8183
1.138
1.561
2.114
2.829
3.744
4.900
6.350
8.150
10.36
13.07
16.34
20.27
24.97
30.52
37.07
44.74
53.65
63.98
75.88
89.51
105.0
122.7
142.7
165.2
190.4
218.6
250.1
284.9
323.5
366.2
413.1
464.6
521.0
4
.0100
.0176
.0306
.0441
.0768
.1248
.1955
.2891
.4203
.6009
.8462
1.175
1.610
2.178
2.911
3.848
5.031
6.513
8.351
10.61
13.37
16.70
20.70
25.48
31.13
37.78
45.57
54.62
65.10
77.17
90.97
106.7
124.6
144.8
167.6
193.1
221.6
253.4
288.6
327.6
370.7
418.1
470.0
526.9
5
.0095
.0168
.0289
.0489
.0810
.1302
.2035
.3004
.4359
.6222
.8750
1.213
1.660
2.243
2.995
3.954
5.165
6.680
8.557
10.86
13.67
17.07
21.14
26.00
31.75
38.50
46.41
55.60
66.23
78.46
92.45
108.4
126.5
147.0
170.0
195.8
224.6
256.7
292.3
331.7
375.2
423.1
475.5
532.9
6
.0089
.0158
.0275
.0517
.0846
.1370
.2118
.3120
.4520
.6442
.9046
1.253
1.712
2.310
3.081
4.063
5.302
6.850
8.767
11.12
13.98
17.44
21.50
26.53
32.38
39.24
47.27
56.60
67.38
79.78
93.96
110.1
128.4
149.2
172.5
198.5
227.7
260.1
296.1
335.9
379.8
428.1
481.0
538.9
7
.0084
.0150
.0259
.0541
.0892
.1429
.2203
.3240
.4586
.6669
.9352
1.293
1.765
2.379
3.169
4.174
5.442
7.024
8.981
11.38
14.30
17.82
22.05
27.07
33.02
39.99
48.14
57.61
68.54
81.11
95.49
111.8
130.4
151.4
175.0
201.3
230.8
263.6
299.9
340.1
384.4
433.1
486.6
545.0
8
.0080
.0142
.0247
.0571
.0932
.1502
.2292
.3364
.4858
.6903
.9666
1.335
1.819
2.449
3.259
4.289
5.585
7.202
9.200
11.65
14.62
18.21
22.52
27.62
33.67
40.75
49.03
58.63
69.72
82.46
97.03
113.6
132.4
153.6
177.5
204.1
233.9
267.1
303.8
344.4
389.1
438.2
492.2
551.1
9
.0075
.0134
.0233
.0598
.0982
. 1567
.2383
.3493
.5035
.7144
.9989
1. 378
1.875
2.521
3.351
4.406
5. 732
7.384
9.424
11.92
14 .96
18.61
22.99
28.18
34.33
41.52
49.93
59.67
70.92
83.83
98.61
115.4
134.4
155.9
180.0
206.9
237.1
270.6
307.7
348.7
393.8
443.4
497.9
557.3
-------
NORMAL TEMPERATURE PSYCHROMETRIC CHART
(ENGLISH UNITS)
O.OM
0.028
0.026
0.024
0.022
0.020
0.018
0.016
O.OM
o
Z
Z)
O
Q-
OL
LU
Q_
O
O-
OL
LU
I—
<
012 u_
0.010
0.006
0.006
0.004
0.002
O
Q
Z
o
Q.
o
>-
H;
O
DRY BULB TEMPERATURE I °F )
-------
^MPERATURE PSYCHROMETRIC CHART
(ENGLISH UNITS)
0.0050
0.0045
0.0040
0.0035
0.0030
0.0025
0.0020
.0.0015
0.0010
0.0005
U_
O
Q
Z
o
o
Q.
c*
LU
<
WO
O
Z
ID
O
Q-
-40
15 20 25 30 35 40 45 50
-_o ^
DRY BULB TEMPERATURE ( °F )
-------
TJ
m
o
O
n
n
HUMIDITY RATIO ( POUNDS OF WATER VAPOR PER POUND OF DRY AIR
-------
SPECIFIC WEIGHT OF DRY AIR IN Ibs/ft3 FOR'F
AND ABSOLUTE PRESSURE OF 29.92 in.Hg
(°F)
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
Specific weight
(Ibs/ft3)
0.08633
0.08449
0.08273
0.08104
0.07942
0.07785
0.07636
0.07492
0.07353
0.07219
0.07090
0.06966
0. 06845
0.06729
0.06617
0.06509
0.06403
Temperature
(°F)
180
200
220
240
260
280
300
350
400
450
500
550
600
700
800
900
1000
Specific weight
(Ibs/ft3)
0. 06203
0.06015
0.05838
0.05671
0.05514
0. 05365
0.05223
0.04901
0.04615
0.04362
0.04135
0.03930
0.03744
0. 03422
0.03150
0.02911
0.02718
KINEMATIC VISCOSITY (ftfsec) OF DRY AIR AT AN
ABSOLUTE PRESSURE OF 29.92 in. HgAND VARIOUS TEMPERATURES °F
Temperature
(°F)
0
20
40
60
80
100
120
150
200
Kinematic viscosity
(ft2/sec)
1.
1.
1.
1.
1.
1.
1.
2.
2.
26 ( 10) '4
36 ( ID)'4
46 ( ior4
58 (lO)'4
69 ( 10)~4
so nor4
89 (ID)'4
07 (ior4
4 (ior4
-------
Compound
Ae*U)d«kvde
Acetic acid
Acetylene
Air
Ammonia
Argon
Bromine. .
Carbon dioiide
dbulnde . .
monoxide
Chlorine
Chloroform
Cyelohexane
DKhlorodifluormethane
Fth.n.
Ethyl alcohol
ether
Etbylene
Helium .
Hexane (n-)
Hydroircn..
bromide
chloride
cyanide
Formu'a
C»H«O
C?H«O
C-H.
NHt
A
CiiHt
Bn
CO
CS-
CO
Clj
CHC1,
-------
VISCOSITY OF AIR (CENTIPOISES) AT ONE ATMOSPHERE
FOR VARIOUS TEMPERATURES °C AND°F
Ttmptiolur*
Dlf.C. Dtg
-100
•-IOO
— 0
100
COO
300 •
40O .
500 -
600 '
700 -
800 -
900-
1000-
100
— 200
-300
.400
500
: — 600
700
- 80O
900
1000
• I IOO
1200
1100
1400
1500
1600
1700
1800
Vitco»ily
Cenlipoiili
-O.I
- 009
- 0.08
- 0.07
- 0.06
T 0.05
- 0.04
- 0.03
- 0.02
001
- 0.009
- 0.008
- 0.007
r- 0.006
- 0.005
(1) centipoise
(Id)'2 gm
cm-sec
_2
(10) poise
2.09UO)'5
H.
f - sec
ft2
2.09(10)"5
slug
ft - sec
6.72(10)"4
ft
m
ft - sec
-------