EPA-600/2-76-088
March 1976
GUIDELINES FOR BURNER ADJUSTMENTS
OF COMMERCIAL OIL-FIRED BOILERS
Oil-Burner Adjustment Procedures to Minimize Air Pollution
and to Achieve Efficient Use of Fuel
Guidelines intended for use
- by skilled service technicians in
adjustment of commercial oil burners.
- as a training guide for advanced
burner service courses.
- as a supplement to manufacturers'
service instructions.
o*
$ *^ T£
U. S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, N. C. 27711
-------
TABLE OF CONTENTS
Page
GUIDELINES FOR BURNER ADJUSTMENTS OF COMMERCIAL OIL-FIRED BOILERS. ... 1
PURPOSE OF THESE GUIDELINES 1
Scope of Commercial Boilers Covered 1
Background Information 2
RECOMMENDED ADJUSTMENT PROCEDURES FOR COMMERCIAL BOILERS ... 3
APPENDIX. BACKGROUND INFORMATION
A. Pollutants of Main Concern A-l
B. Field-Type Instruments and Significance of Measurements B-l
C. Characteristics of Fuel Oils for Commercial Boilers. ....... C-l
D. Emission Characteristics of Commercial Boilers D-l
E. References E-l
F. Short Form Adjustment Procedure for Commercial
Oil-Fired Boilers F-l
ACKNOWLEDGEMENT
These Guidelines were prepared by David W. Locklin and Richard E. Barrett
of Battelle's Columbus Laboratories under EPA Contract No. 68-02-0251, with participa-
tion by representatives of the heating industry and of the Environmental Protection
Agency, including Robert E. Hall, Project Officer. Special acknowledgement is due
the reviewers from industry, including committee members from
- Air Pollution Control Association
- American Boiler Manufacturers Association
- American Petroleum Institute
- National Association of Oil Heat Service Managers
- National Oil Fuel Institute.
This report has been reviewed by the Environmental Protection Agency and is
approved for publication. Any mention of trade names or commercial products does
not constitute endorsement by the Government or its contractors. This report may
be reproduced or reprinted if reference is made to the U. S. Environmental
Protection Agency and to report number EPA-600/2-76-088.
-------
GUIDELINES FOR BURNER ADJUSTMENTS
OF COMMERCIAL OIL-FIRED BOILERS
In the past, the most important reason for adjustment of oil burners has been to
ensure reliable automatic operation. A second important reason has been to provide efficient
fuel utilization. Common good practice of adjusting a burner for minimum air setting, con-
sistent with acceptable smoke levels, is an effective way of meeting both objectives.
Recently, a third objective has been added; that of minimizing air pollution.
It is important to recognize that any burner adjustments for this purpose must still
meet the former requirements. Fortunately, adjustments for low air-pollutant emissions
can still meet the objectives of reliable and efficient operation.
PURPOSE OF THESE GUIDELINES
,4 "" " — '
These Guidelines have been prepared (1) for use by skilled service technicians
or skilled operators in adjusting commercial oil-fired boilers and (2) as an aid to
service managers engaged in training of service technicians. By following these Guide-
lines, the skilled oil-burner service technician will be able to adjust commercial oil
burners to minimize air pollution and get the most useful heat from the fuel fired.
The Guidelines should be used as a supplement to the equipment manufacturer's
installation and service instructions and the handbooks and manuals on good service
practice developed by oil-heating industry specialists' ' . These Guidelines add the
perspective of minimizing air-pollutant emissions.
Scope of Commercial Boilers Covered
The recommendations and discussions in these Guidelines apply to adjustment of oil-
fired boilers larger than residential sizes but smaller than industrial sizes — they apply
to oil-fired boilers of cast iron, firetube, and watertube construction. The capacity range
of "commercial boilers" considered in these Guidelines is approximately as follows in terms
of firing rate, Btu output, and boiler horsepower:
**
Oil firing rate 3 to 100 gallons per hour
Btu output -— 300,000 to 10,000,000 Btu per hour
Boiler horsepower 10 to 300 BHP.
The principles in these Guidelines also apply generally to any single-burner boiler in the
industrial size range.
* References are included in Appendix E.
** Separate Guidelines are being issued by EPA covering adjustments for residential oil
burners generally having oil firing capacities below 3 gallons per hour (Report
Number EPA-600/2-75-069-a)•
-------
Background Information
In addition to recommended adjustment steps, these Guidelines include pertinent
background material that will aid in the overall understanding of air pollutants and
their control by combustion adjustments for commercial boilers. Additional information
is provided in the Appendix on the following topics:
A. Pollutants of Major Concern
B. Field-Type Instruments and Significance of
Measurements
C. Characteristics of Fuel Oils for Commercial
Boilers
D. Typical Emission Characteristics of
* Commercial Boilers
E. References
F. Short-Form Adjustment Procedure for Commercial
Oil-Fired Boilers.
Burner service organizations may wish to develop their own short-form recommendations that
tie in with overall company policy, service training doctrine, abilities of service
technicians, and local regulations. Appendix F is an example short form.
Fuel Conservation —
An Indirect Approach to Emission Control
In addition to burner adjustments for efficient boiler
operation, attention should also be called to the importance of
fuel conservation by reducing demands on the boiler. The burner
technician can perform an additional service by advising the
building owner as to opportunities for reducing heating loads by
modifications in the building or its operation (for example,
better insulation and weather stripping, clock operation or set-
back of thermostats for intermittent occupancy, and reduced
ventilation air). Reductions in heating load can have an important
benefit in reducing overall pollutant emissions.
-------
RECOMMENDED ADJUSTMENT PROCEDURES
FOR COMMERCIAL BOILERS
The following procedures are recommended for adjustment of oil-fired commercial
boilers and are supplemental to manufacturers' instructions and other service handbooks(1~
1. CLEAN &
SEAL
Clean the boiler heat-transfer surfaces, flue passages,
and burner if needed—especially the atomizer and air-
handling parts. Seal any air leaks affecting the
combustion chamber or flue passes.
2. SET OIL
PREHEAT
Be sure that the oil to be fired is suitable for the
installation. (See Appendix C for information on
grades of fuel oil.)
Use the proper oil temperature for pumping and atomiza-
tion. Firing a boiler with either too high or too low
a preheat temperature can give poor combustion performance.
Check the manufacturer's operating manual to determine
the proper oil temperature for firing a particular fuel.
(See Figure 4 in Appendix C for viscosity-temperature
chart for different fuel oil grades.)
Special attention should be paid to selecting preheat
temperatures for low-sulfur oils (which may have become
available since the operating manual was written). Some
low-sulfur oils have unusual viscosity-temperature rela-
tionships.
Normally, the preheat temperature should be adjusted for
the following oil viscosity ranges (at the nozzle).
Usual Range of Firing Viscosity
Atomization
Method
Pressure
Steam or Air
Rotary
Saybolt Seconds
Universal
35-150 SSU
35-250 SSU
150-300 SSU
Equivalent
Kinematic
Viscosity,
centistokes
4-32 cs
4-55 cs
32-60 cs
If the viscosity of the particular fuel is unknown, start
at 250 degree F preheat level and back off to lower preheat
temperature until best combustion performance is obtained.
-------
8
.o
E 6
D
z
0)
jc
o
E
on
-5 ^
o
o
o
GO
High air settings
\ Normal adjustment range
Tolerance to "knee"
Low air settings
Smoke-CO, Curve
"Best" air setting1
M.. II
Knee
8 10 12
Percent C02 in Flue Gas
14
Figure 1. Smoke-CO2 Characteristic for a Typical
Commercial Oil Boiler Firing Residual
Oil — With Recommended Air Adjustment
-------
3. ADJUST
INPUT
4. SMOKE -
C02
CURVE
Adjust the atomizing pressure to manufacturer's recommen-
dations and the fuel input to full firing rate, giving
consideration to the firing rate required for the con-
nected load. Make sure atomizing nozzle is the type and
capacity recommended by the manufacturer.
The objective of the procedure outlined below is to attain
the highest practical C0« value without exceeding the smoke
limits listed below. (S.ee Appendix B on field type instruments.)
The sampling hole in the stack for smoke and CCL readings should
be located between the boiler and the draft control. Ideally,
the sampling point would be in a straight section of duct, at
least 8 diameters from the boiler or any upstream flow disturb-
ance (bend, etc.) and at least 2 diameters from the draft
control or any downstream flow disturbance. Sometimes, shorter
distances from flow disturbances must be accepted due to space
limitations.
The sampling tube inlet should be positioned to draw a representa-
tive gas sample. This is generally accomplished by positioning
the inlet end of the sampling tube near the centerline of the
duct.
Using an air setting for clean combustion, operate the oil
burner at full firing rate until equilibrium is reached,
usually indicated by a steady reading on the stack thermom-
eter. Take readings of smoke and CO- sufficient to
visualize the position of the characteristic curve as shown
in Figure 1. This can be done by adjusting the control
linkage and/or damper settings for several air settings
over a range and by taking smoke and CC>2 readings at each
point. Plot the readings on a chart or graph paper like
the sample in Figure 2.
5. ADJUST
AIR
SETTING
For the full firing rate, determine the location of the "knee"
where the smoke curve begins to sharply break upward, as shown
in Figure 1, then adjust the air setting to near the low CO-
side of the "knee" of the smoke curve, about 1/2 percent C02
lower than the "knee".
For most commercial boilers, it should be possible to adjust
for smoke levels below the following "maximum desirable"
Bacharach smoke numbers. These smoke levels can usually be
met with good practice.
-------
o>
JQ
S
o
o
o
o
o
CD
y
8
7
6
5
4
3
2
I
0
678 9 10 1 12 13 14 15 l<
Percent COa in Flue Gas
Figure 2. Sample Graph Paper for Service Technician's
Plot of Smoke-CC>2 Characteristic
-------
Fuel Grade
Maximum Desirable
Bacharach Smoke Number
No. 2 1 or less
No. 4 2
No. 5 (light and heavy), 3
and low-sulfur resid
No. 6 4
Keep in mind that high C02 settings are important for
good thermal efficiency (see Appendix B). Therefore,
adjust for the highest practical CC>2 level without
excessive smoke.
6. DIAGNOSE
ANY PER-
FORMANCE
PROBLEMS
You should be able to adjust the burner to operate with
smoke levels below the "maximum desirable" listed above,
while maintaining the CQy value at 12 percent or higher.
If not, it is likely that the atomization and/or fuel-
air mixing are poor. Make sure that the proper nozzle
is installed and that the nozzle is clean. Check the
atomizing pressure and preheat, trying different temper-
atures if necessary. Check the air handling parts.
7.
ADJUST
AIR
CONTROL
LINKAGE
For modulating burners, apply the procedure in Steps 4
and 5, then repeat at low-fire setting and at an
intermediate firing rate. Typically, the optimum air
setting at low fire will be at a lower CO- than for the
high-fire condition.
The control linkage should proportion the air at inter-
mediate load settings; however, several points at inter-
mediate firing rates should be checked for CO- and smoke
to validate linkage settings throughout the range. It is
often convenient to use a felt pen to mark linkage setting,
so as to retrace the direction and position of adjustments.
8.
ADJUST
FOR GAS
FIRING,
If the boiler is equipped for gas firing, use a similar
procedure to adjust for operation on gas. However, maxi-
mum C0~ readings for gas are somewhat lower than for oil.
(See Figure 5, Appendix C). Equivalent values of CO- for gas
and oil at different excess air levels are as follows:
-------
Percent CO, in Flue
Percent
Excess Air
0
10
25
50
75
Gas
Firing
12.0
10.8
9.4
7.9
6.6
No. 1 Oil
Firing
15.0
13.5
11.8
9.8
8.3
Gas
No. 6 Oil
Firing
16.5
15.0
13.0
11.0
9.3
As gas-fired units frequently emit CO at low air settings
(before smoke is detected), it is necessary to check for
CO at the extremes of the air-adjustment range, using a
suitable CO detector. CO readings should not exceed 0.04
percent (400 ppm). See Appendix A.
On dual-fuel-fired units, after the gas settings are made,
the oil settings must be verified. It is frequently
impossible to obtain optimum performance on both fuels at
both high- and low-fire rates; a compromise must be made
in such cases.
9. CHECK
IGNITION
Adjust ignition electrodes to the manufacturer's recom-
mendation. Make sure ignition occurs promptly at light-
off firing rate. This will avoid startup emissions and
deposits of unburned oil.
10. SCHEDULE
BOILERS
For multiple boiler installations, arrange the master
control system so that individual boilers avoid opera-
tion at low fire or at full load for extended periods.
Emissions are usually lowest and efficiency highest when
boilers are operated at about 50 to 80 percent of rated
load. Avoid excessive on-off cycling, since emissions of
smoke, particulate, CO, and hydrocarbons tend to peak on
startup and shutdown.
11. ANNUAL An annual overall tune-up, and safety check by a competent
PTTFCKUP
service technician is strongly recommended.
Adjustment by these procedures will be effective in assuring minimum air-pollutant
emissions from commercial boilers and, at the same time, achieve a reasonable compromise with
efficiency of fuel utilization.
-------
A-l
APPENDIX: BACKGROUND INFORMATION
Information on the air-pollutant effects of different burner adjustment
procedures have been developed in recent field and laboratory investigations^"8),
including those conducted cooperatively by the U. S. Environmental Protection Agency
and the American Petroleum Institute^ '. The findings of these investigations,
combined with good field practice, are the basis for these Guidelines.
This Appendix contains additional background information as follows:
A. POLLUTANTS OF MAIN CONCERN
B. FIELD-TYPE INSTRUMENTS AND SIGNIFICANCE
OF MEASUREMENTS
C. CHARACTERISTICS OF FUEL OILS FOR COMMERCIAL
BOILERS
D. TYPICAL EMISSION CHARACTERISTICS
OF COMMERCIAL OIL BURNERS
E. REFERENCES
F. SHORT FORM ADJUSTMENT PROCEDURE FOR COMMERCIAL
OIL-FIRED BOILERS.
-------
A-2
A. POLLUTANTS OF MAIN CONCERN
Pollutants and Their Measurement
The air pollutants of main concern for the purposes of these Guidelines can be
divided into three broad classes, depending upon how much the serviceman can control them
by his adjustments. These classes are
Class 1. Pollutants that may result from incomplete combustion
and are generally strongly affected by burner adjust-
ment procedures:
• Smoke and particulate *
• Carbon monoxide, CO
• Hydrocarbons, HC.
Class 2. Pollutants only partially affected by burner adjustment
procedures (and not recommended as adjustment criteria).
• Nitrogen oxides: NO and N0_ (usually considered
together and identified as NO ). **
Class 3. Pollutants not affected by burner adjustment procedures
but depending only on sulfur content of the fuel.
• Sulfur oxides (mainly S02 with traces of
so3).
The following comments describe each of the Class 1 pollutants from the viewpoints
of definition, hazards associated with the pollutant, how it is detected or measured, and how
emissions of the pollutant are affected by service adjustments. (The Class 2 and Class 3
pollutants are not discussed further here, because the serviceman has little or no control
over them by adjustment.)
* Particulate that is formed from the ash content of fuel oil is not affected by burner adjust-
ments. However, the carbon or soot portion of particulate, usually the larger portion, can
be strongly affected by burner adjustments.
** Emissions of NOX are generally greater with heavier grades of fuel because of usually higher
content of fuel-bound nitrogen.
-------
A-3
Smoke and Particulate
Smoke consists mainly of tiny unburned particles of carbon. Smoke has long been
an important factor in the adjustment of oil-burning equipment to avoid fouling of heat-
transfer passages with soot, to achieve efficient fuel utilization, and to avoid general
complaints resulting from visible smoke and fallout of larger particles.
Over the past 25 years, the development and the use of the filter-paper method of
smoke measurement (as used, for example, in tne Bacharach Smoke Tester) has allowed a much
(2 3 9)
more sensitive measurement than by visual means such as the Ringelmann Scale ' ' . The
method is now an accepted ASTM standard and is widely used in the oil-burning industry
to assist in field adjustments ' . This type of smoke tester is a key tool for the
service technician.
Smoke and CO. measurements, considered with the perspective presented in these
Guidelines, provide a simple and relatively reliable means to avoid high emissions of other
pollutants.
Smoke and particulate are related. Particulate is the usual scientific term
applied to air-pollution measurements in terms of weight of solid and liquid materials being
emitted to the atmosphere. "Particulate" is defined by the U.S. Environmental Protection
Agency as "any finely divided solid or liquid material, other than uncombined water, as
measured by EPA Method 5»(12>13).
Particulate is composed of unburned fuel, carbon or soot, ash constituents in the
fuel, and noncombustible-airborne dust that enters with the combustion air.*
Coarse particles do not carry far in the atmosphere and usually fall out near the
stack. Fine particles, the predominant portion of particulate from oil burning, can remain
in the atmosphere for long periods and can obscure long-range visibility. In addition, fine
particles can deposit on lung tissues and result in respiratory impairment if present in high
concentrations. These are the reasons that particulate is of concern to air-pollution
control.
The serviceman can exert considerable control over particulates by ensuring that
the fuel pump and safety shut-off valve have good cutoff characteristics, and by the burner
adjustments he chooses.
Ash content is extremely low for No. 2 heating oil, usually below 0.005 percent. For No. 6
oil, the ash content is typically below 0.05 percent. The ash content for other grades
usually falls between these limits.
-------
A-4
Participate measurements by EPA standard measuring techniques require special equip-
ment and techniques, plus long sampling periods, which are neither practical nor necessary
for most commercial boiler adjustments. For steady operation, smoke measurements by the
filter-paper method are the most practical method to warn of high particulate levels, as
discussed in Appendix D.
Carbon Monoxide, CO
CO is a toxic gas formed by incomplete combustion. When equipment is in good
adjustment, CO levels are very low. But with improper combustion, CO emissions can reach
dangerous levels if gases should leak into living spaces. When the low levels of CO that
are emitted by properly operating oil-heating equipment are diluted in the atmosphere, CO
is not considered dangerous and is depleted with time in the atmosphere.
For field adjustment of most conventional oil-fired commercial equipment by methods
suggested in these Guidelines, it is seldom necessary to measure CO except when firing gas
in dual-fuel boilers. With oil firing, smoke measurement can be used as an indicater of
poor combustion that could lead to the onset of CO at low excess-air levels (high C0? levels).
However, if the serviceman increases the air setting too far, CO levels occasionally will
increase rapidly without smoke; therefore, the air setting should not be increased beyond
that necessary to obtain a satisfactory smoke reading below the "knee" on Figure 1.
CO measurements are desirable when checking adjustments for gas firing
on dual-fuel commercial boilers. For detection and measurement of CO at the low levels
usually encountered in heating equipment*, CO instruments using color-sensitive tubes are
currently the most practical and economical method for field use by servicemen.
Hydrocarbons. HC
Emission of hydrocarbons from oil-burning equipment occur when combustion is
incomplete; they can consist of unburned or partially burned fuel vapors.
Although hydrocarbons are generally not toxic to the same extent as CO or NOX,
they can be accompanied by unpleasant odors, and can contribute to photochemical smog
in the atmosphere. Essentially, no hydrocarbons are emitted when oil heating equipment
is properly adjusted.
* As a point of reference, standards for most gas-fired appliances specify a maximum
limit of 0.04 percent CO or 400 parts per million on an air-free basis.^ '
-------
A-5
If large amounts of unburned oil vapor should be emitted from an improperly oper-
ating installation, this can be detected as oily or yellow deposits on the filter paper
during smoke measurements. At lower levels of hydrocarbon emissions, the emissions generally
follow the trends of smoke or CO emissions and, hence, these measurements are usually a good
indicator of whether hydrocarbon emissions are high or low (except at extremely high air
settings where smoke readings may fail to indicate a rise in hydrocarbons). See Appendix D.
For routine adjustment of commercial oil burners in the field, it is not necessary
to measure hydrocarbons. If the serviceman detects hydrocarbon odors (unburned oil vapor)
near the burner or near a barometer draft control, he should check for flame impingement,
improper nozzle size, improper adjustment of the combustion head, or improper pump cutoff
on shutdown.
-------
B-l
B. FIELD-TYPE INSTRUMENTS AND SIGNIFICANCE
OF MEASUREMENTS
For the adjustment procedures outlined in these Guidelines, it is assumed that the
oil-burner service technician is accustomed to using field-type instruments. A typical
kit includes the following:
• CO. tester for stack-gas analysis
- Usually a simple wet-chemical absorbent-type
analyzer (for example, Fyrite or Orsat apparatus).*
- CO. readings are used to provide an indication of
the combustion air setting.
• Smoke tester and shade scale
- hand-pump version of the ASTM filter-paper method
for smoke determination.
- includes a shade scale for evaluating smoke spots
from 0 to 9 (Bacharach or ASTM scale). (This is
not a Ringlemann scale. Smoke levels below about
5 on the Bacharach scale are generally not visible
from a small stack against the sky.)
• Thermometer for measuring stack temperature
- usually the dial type, but liquid thermometers are
more accurate.
• Draft Gauge
- for draft measurements in the breeching or overfire,
usually diaphragm type or a suitable manometer.
• CO detector for gas-fired commercial boilers
- usually color-sensitive chemical in tubes.
Instruments which combine several of these readings in one device are being introduced to the
market and offer convenience in use.
Some additional comments are in order with respect to CO- and smoke measurements.
The Significance of C0~ Measurements
CO readings are used to identify how much combustion air is being supplied to the
burner, compared to the theoretical amount required for combustion. It is seldom possible to
burn a fuel completely and cleanly unless air in excess of the theoretical amount is provided.
* For more complete and accurate measurement of flue gas composition for adjustment of large
equipment, a 3-tube conventional Orsat apparatus (CO-, £>„, and CO) is recommended so a
complete flue-gas analysis can be measured.
-------
B-2
The following values will illustrate the relationship between excess air supplied for combus-
tion and the CO- concentration in the flue gas. Comments on combustion performance and
efficiency are also indicated.
Air /Fuel
Mixture
Settings
Theoretical or
"Chemically Correct"
Mixture
Typical for
Residential Equipment
(below AOO.OOO Btu/hr
output)
Typical for
Commercial Boilers
* Assumes satisfactory
Excess-Air Supply CC^ Comments on
(percent above in Flue Gas Combustion
theoretical)
0 %
35 7.
70 %
150 %
16 7.
35 7.
70 7.
smoke levels and
No. 2 Oil
15 7.
11 7.
9 7.
6 7.
13 7.
11 7.
9 7.
negligible CO
No. 6 Oil Performance*
16.5 7. "Stoichlometric mixture"
(cannot be achieved for
reliable operation in
practice)
Excellent performance
Typical performance
Poor performance
14 7. Excellent performance
12 % Typical performance
9.5 7o Poor performance
in stack gas.
The overall efficiency of fuel utilization is lowest at the low levels of CO (high excess
air), because the products of combustion are diluted by the excess combustion air and more
hot gas is lost up the stack.
The Significance of Smoke Measurements
The ASTM filter-paper method of smoke measurement is useful in assessing the soot-
ing characteristics of a combustion process, so adjustment can be made for clean burning. '
In this method, a measured sample is drawn through a filter paper and smoke spots are com-
pared to a standard shade scale, commonly known in the oil-heating trade as the "Bacharach
shade scale".'3'' The method offers a practical and sensitive means of judging the combus-
tion process and can be used as a rough indicator of particulate emissions during steady-
(7 81
state operation. '
The following table provides comments on combustion performance and sooting as
they relate to smoke readings.
-------
B-3
Bacharach
Smoke
Less than
No. 1
No. 1
No. 2
Comments on Combustion Performance^8^
No. 2 Oil
Excellent
Good
Fair
Residual OllW
Excellent
Excellent
Good
Comments on Sooting of
Heating Surfaces Anticipated
(Reference 3)
Minimal
Extremely light
Slight sooting which will not
Increase stack temperature
appreciably
No. 3 Typical for Good May be some sooting but will
untuned burner rarely require cleaning more
than once a year
No. It Marginal Acceptable for Some units will require
No. 4 & 5 oil & LSR. cleaning more than once a
Good for No. 6 year
No. S Unacceptable Poor to unacceptable Potential for rapid and heavy
or higher soot buildup
(a) Assuming satisfactory COj levels. (b) Grades No. 4, 5, and 6, plus low-sulfur
resid (LSR).
For reliable smoke readings, It is important that the manufacturer's instructions
with the smoke tester be followed carefully. For example, the sample should be pumped
slowly from the stack with full strokes, with several seconds pause at the end of the pull
strokes to allow a full sample.^ '
The Significance of Stack Temperature;
Its Effect on Efficiency
Stack temperature is significant in determining the effectiveness of fuel utiliza-
tion, because it is an indicator of the amount of heat lost up the stack.
Stack temperature can be considered to be abnormally high if the net stack tem-
perature (actual stack temperature minus boiler room temperature) exceeds 400° to 500° F for
matched package units, or 500°to 600°F for conversion boilers. A high stack temperature
reading may indicate one of the following conditions:
1. Excessive firing rate for the amount of heat-transfer
surface in the boiler.
2. Dirty or soot-covered heating surfaces.
3. Need for effective baffling of flue passes (in the
case of boilers converted from coal firing).
4. Improper adjustment or control of the draft, usually
excessive draft through the unit.
These points should be checked and remedied if stack temperatures are abnormally high.
-------
B-4
"Overall thermal efficiency" (or "boiler efficiency")* is defined as the proportion
of the heat energy in the fuel that is actually converted to steam or hot water during
continuous burner operation. The principal losses are
• Heat loss up the stack and
• Heat lost from the boiler jacket through
its insulation
The heat lost up the stack can be important and can be affected by the burner
adjustments. The factors used to assess this loss for a given fuel are
• Net stack temperature (actual stack temperature
minus the boiler room temperature) and
• Percent C02 in the flue gas.
Figure 3 shows the combined effects of these two factors on thermal efficiency. For high
efficiency, it is desirable to operate the boiler with low net stack temperature and high
CO, in the flue gas, consistent with a satisfactory smoke level. With most modern package
commercial boilers, a boiler efficiency of 80 percent can be achieved with satisfactory
smoke level when the boiler is operating continuously at rated load.
Seasonal efficiency is less than the continuous boiler efficiency at full firing
rate, because of possible less-efficient operation at part load or low-fire operation and
because of heat losses from the unit during off periods. Seasonal efficiency will be
highest for installations that
1. Have high boiler efficiency during continuous operation
(i.e., low stack temperature and high CCL, with acceptable
smoke)
2. Have a steady load that allows them to operate predominantly
at their "base load" firing range where they are most
efficient
3. Have relatively little cycling to low-fire setting or to on-
off operation
4. Have good performance during starting, shutdown, and modula-
tion, such that heating surfaces remain clean.
* Overall thermal efficiency is sometimes referred to as "combustion efficiency", but it is
also dependent on the effectiveness of the boiler heat-transfer surfaces.
-------
B-5
Net Stock Temperature
400 F
50
Percent C02 in Flue Gas
Figure 3. Effect of Stack Temperature and CCX on Overall Thermal
Efficiency
Basis: • Continuous operation
• No. 2 heating oil
• Heat lost from jacket is assumed
to be useful heat.
Source: Bulletin 42, University of Illinois, Engineering Experiment
Station Circular Series 44 (June 1942).
-------
C-l
C. CHARACTERISTICS OF FUEL OILS
FOR COMMERCIAL BOILERS
In fuel selection, it is important that the grade of oil is not heavier than the
equipment is specifically designed to handle. For example, if the heavier grades of oil are
to be used (No. 5 and No. 6), the system must be equipped for preheating upstream of the
atomizer. For the heaviest grade of oil (No. 6), preheating of the oil is required for
handling either at the tank or in a circulating system.
Basic grades of fuel are outlined in Table 1. This identifies the traditional
grades of fuel defined in the ASTM standards, graded mainly according to viscosity.
In addition, the table provides a description of "low-sulfur resid" which is a category
rapidly replacing conventional residual oil grades in local areas subject to sulfur regula-
tions. The viscosity of low sulfur resid is usually in the range for No. 5 oil, but shifts
in crude sources and refinery practices may change this pattern. *•
In Table 1, viscosity values in brackets and typical API gravity values are averages
efined fuels taken from tV
do not include imported fuel oils.)
for U.S. refined fuels taken from the 1975 ERDA survey on heating oils . (These averages
Figure 4 illustrates typical viscosity-temperature relations for ASTM
grades of fuel oil. In general, any given fuel will have a viscosity-temperature slope
parallel to those shown on Figure 4 for the boundaries of the grade ranges . Some low-
sulfur residual oils have viscosity-temperature lines parallel to those shown on Figure 4
at high temperatures (above 140 F) but deviate toward even higher viscosity than predicted
by these lines as the oil is cooled near the pour point. However, their viscosity in the
firing range and their overall burning qualities make their handling and combustion perform-
ance generally superior to the traditional high-sulfur fuels
In general, the No. 2 or No. 4 grades of fuel are more practical for smaller
commercial boilers. They are also preferred as a standby fuel where interruptible gas
is normally fired. The heavier grades of fuel oil demand more costly fuel handling facilities,
greater care in adjustment of equipment, and greater overall maintenance.
Effect of Fuel Characteristics on Emissions v
Characteristics of fuels available for commercial burners have an effect on
smoke and particulate emissions. However, fuel characteristics have little effect on CO
or HC, if the fuels are properly handled.
-------
TABLE 1. FUEL OIL DESIGNATIONS AND TYPICAL CHARACTERISTICS
GRADE
(a)
DESCRIPTION AND APPLICATION
PREHEATING REQUIREMENT
For Pumping For
and Handling Burning
VISCOSITY RANGE
Saybolt Universal
at 100 F125-300 SSU
[200]
Yes
Yes
Usually
Yes
(c)
>300-900 SSU
[550]
>900-9000 SSU
[5000]
45-9000 SSU
42
35
19
18
16
13
(a)
(b)
(c)
(d)
(e)
Grade numbers No. 1, No. 2, No. 4, No. 5 (light), No. 5 (heavy), and No. 6 are ASTM designations .
"Low-sulfur resid" is a recent term used to describe residual oil grades recently shipped to meet local regulation;
it is essentially replacing No. 5 and No. 6 where sulfur regulations are in effect, for example, along the East
Coast. (The sulfur content of this grade of fuel oil is generally 1 percent, or less.) The viscosity of present
low-sulfur resid is in the range of No. 5(16) (it is not clear what the viscosity of these fuels may be in the
future.)
Preheating requirement depends on pour-point and viscosity in relation to climate.
May require heating for burning when using mechanical atomization.
Viscosity limits specified by ASTM D396-75 for number grade shown. Range for low-sulfur resid is estimated.
Average viscosity for U.S. refined fuels from ERDA Heating Oils Survey, 1975'^', is shown in brackets and is
presented as a typical value.
(f) Average API gravity for U.S. refined fuels from ERDA Heating Oils Survey, 1975
(17)
-------
C-3
10,000
5000
2000
I00°
n
•0
c
500
- 400
2 300
w
0)
D
o
n
>s
o
<*>
i
o
u
in
200
150
100
80
60
50
40
1 I I T
60
100 150 200
Oil Temperature, degrees F
3000
2000
1000
500
at
100 2
50
20
c.
-------
C-4
Generally, the lighter grades of fuel produce less smoke and lower emission of
particulate. For example, in a field investigation when different fuels were fired
by normal practice in the same boilers at similar conditions, particulate levels with No. 2
oil averaged only 4 percent of that for conventional No. 6 oil. Particulate for a typical
low-sulfur resid (1 percent sulfur) averaged 30 percent of the level for a conventional
No. 6 oil. This indicates that the blending and treatment to meet sulfur regulations for
the new low-sulfur resid has the additional effect of providing a cleaner burning fuel
than from conventional No. 6 oil.
Figure 5 shows the smoke-CCL characteristic of a typical commercial boiler firing
three different grades of fuel oil (and natural gas). Other boilers show similar character-
istics when firing different fuels. [The smoke characteristic with gas firing is also shown;
it should be noted that the CCL level for natural gas is always lower than for fuel oils
operating at the same excess-air level.]
Emissions of NO are generally higher with the heavier grades of fuel oil due to
higher content of nitrogen in heavy oil. As pointed out in Appendix A, the service
technician has relatively little control over NO emission levels within the range of adjust-
X
ment available to him for a given burner-boiler combination in the commercial boiler size
range.
6
D
Z
on 2
I I
No. 6 oil
I I
8 K> 12
Percent C02 in Flue Gos
Figure 5. Smoke-CO, Characteristic of a Typical Commercial
Boiler Firing Three Different Grades of Fuel Oil
and Natural Gas
-------
C-5
Sulfur in crude oil tends to stay with the heavier fractions during refining.
Hence, S0~ emissions can generally be expected to be higher with heavier grades of fuel,
unless special refining treatment is provided, as is generally the case with low-sulfur
resid. Until practical SO- removal systems become commercially available for small equip-
ment, the service technician has no control over S0« emissions by his adjustment. At
present, the most practical and economical method of SO- control for commercial boilers
is by fuel selection.
-------
D-l
D. EMISSION CHARACTERISTICS
OF COMMERCIAL BOILERS
Effect of Air Setting
Figure 6 shows typical emission characteristics as affected by air setting for
a commercial boiler operating at 80 percent load. Emissions of concern include smoke, CO,
)1C, and NO . Emissions of CO or HC are generally low within the normal range of CO-
X £
settings for oil-fired commercial boilers.
For oil firing, smoke rises sharply as the CO- setting is increased beyond the
knuckle of the smoke curve; as the CO- setting continues to be increased, CO and HC emissions
rise. Because the smoke curve usually begins to rise at lower CO,, levels than the CO and HC
curves, low smoke is a good indicator to prevent excessive CO and HC emissions. At the other
extreme, as low CO,, settings are approached, the CO and HC emissions may rise before smoke
rises. However, setting the boiler to operate at the highest C02 level without excessive
smoke avoids operation at the low CO- conditions (as discussed on page 5). (NO levels
are not greatly influenced by air settings within the normal operating range where smoke
and CO- are acceptable.)
For gas firing as high CO- values are approached, the CO curve usually rises
sharply before smoke rises. Thus, use of a CO detector is recommended for minimizing
emissions from commercial boilers firing gas.
Effect of Load
Figure 7 illustrates the characteristic curves of smoke versus C0_ for a typical
commercial boiler firing residual oil at two different loads (or firing rates). For
modulating boilers that vary firing rate according to load, particulate levels are usually
(but not always) higher at higher load operation than at mid-load. At low-fire operation,
the air velocity of the combustion air is frequently reduced below that required for good
mixing. This results in a poorer smoke CO- curve, as shown in Figure 7. Thus, it is
common practice to set the air/fuel proportioning linkage to provide for a higher air
setting (and lower CO- levels) at low fire.
For multiple boiler installations, particulate levels will generally be minimized
if the boilers are programmed to operate at less than full load (say 50 to 80 percent load).
Also, it is preferable to avoid operation at low fire, as this may result in higher emissions.
Excessive on-off cycling should be avoided..
-------
D-2
6 10 12
Percent C02 in Flue Gas
14
Figure 6. Gaseous Emissions Characteristic for a Typical
Commercial Boiler as Influenced by Combustion
Air Setting
£ 6
3
Z
01
J£
O
o
on
25% load or
lOW fire Typical
low-fire
air setting
80% load
I
Typical
high-fire
air setting
10 12
Percent COz in Flue Gas
14
Figure 7. Typical Smoke-CC>2 Characteristic for a Commercial
Boiler at Two Loads
-------
E-l
E_. REFERENCES
1. "Guide for Installation and Operation of Oil-Burning Units", prepared by the
American Boiler Manufacturers Association, under Contract CPA 22-69-133, for the
National Air Pollution Control Administration (August 15, 1970)*.
2. "Evaluate Burner Performance", Fueloil and Oil Heat, October, 1973, p 36.
3. "Oil Burner Combustion Testing", Bulletin 4011. Available from Bacharach Instru-
ment Company, 625 Alpha Drive, Pittsburgh, Pennsylvania 15238.
4. Domestic and Commercial Oil Burners — Installation and Servicing. C. H. Burkardt,
Third Edition, McGraw-Hill Book Company, New York (1969).
5. "A Study of Air Pollutant Emissions from Residential Heating Systems", R. E. Hall,
J. H. Wasser, and E. E. Berkau, Environmental Protection Agency, Report No. EPA-
650/2-74-003 (January, 1974). NTIS Report PB-229,667**.
6. "A Field Investigation of Emissions from Fuel Oil Combustion for Space Heating",
A. Levy, S. E. Miller, R. .E. Barrett, E. J. Schulz, R. H. Melvin, W. H. Axtman,
and D. W. Locklin. A report by Battelle-Columbus Laboratories to the American
Petroleum Institute. API Publication No. 4099 (November 1, 1971)***.
7. "Field Investigation of Emissions from Combustion Equipment for Space Heating",
R. E. Barrett, S. E. Miller, and D. W. Locklin. A report by Battelle-Columbus
Laboratories to the U.S. Environmental Protection Agency and the American Petro-
leum Institute. EPA Report R2-73-084a (June, 1973). API Publication No. 4180**.
NTIS Report PB-223,148**.
8. "Investigation of Particulate Emissions from Oil-Fired Residential Heating Units",
R. E. Barrett, D. W. Locklin, and S. E. Miller. A report by Battelle-Columbus
Laboratories to the U.S. Environmental Protection Agency and to the American
Petroleum Institute. EPA Report No. EPA-650/2-74-026 (March, 1974). NTIS Report
PB-273,355**.
9. "Smoke Measurement in a Fuel Oil Test Unit", D. W. Locklin, and G. V. Parmelee,
ASHVE Research Laboratory, ASHVE Transactions, 57. 1951, p 129.
10. "Standard Method of Test for Smoke Density in the Flue Gases from Distillate Fuels",
ASTM 02156-65(70). ASTM Standards for Petroleum Products (Part 17).
11. "Standard Method of Test for Effect of Air Supply on Smoke Density in Burning Dis-
tillate Fuels", ASTM D2157. ASTM Standards for Petroleum Products (Part 17).
12. "Standards of Performance for New Stationary Sources", Federal Register, 37. No.
55, Part I, March 21, 1972, p 5767.
13. "Chemical Composition of Particulate Air Pollutants from Fossil-Fuel Combustion
Sources", L. J. Hillenbrand, R. B. Engdahl, and R. E. Barrett. A report by
Battelle-Columbus Laboratories to the U.S. Environmental Protection Agency on EPA
Contract EHSD 71-29 (March 1, 1973). NTIS Report PB-219009**.
14. Gas Engineers Handbook. Edited by C. G. Segeler, The Industrial Press, 1965,
pp 2-49.
15. "Specifications for Fuel Oils", ASTM D-396-75. ASTM Standards for Petroleum
Products (Part 17), American Society for Testing and Materials, 1975.
16. "Low-Sulfur Fuels are Different", by C. W. Siegmund, Hydrocarbon Processing, Feb-
ruary, 1970, pp 89-95.
17. "Burner Fuel Oils, 1975", by E. M. Shelton, Bartlesville Energy Research Center,
BERC/PPS-75/2 (August, 1975), available from U.S. Energy Research and Develop-
ment Administration, Bartlesville, Oklahoma.
* Available from American Boiler Manufacturers Association, Suite 317, AM Building,
1500 Wilson Boulevard, Arlington, Virginia 22209.
** Available from National Technical Information Service, Springfield, Virginia 22151.
*** Available from American Petroleum Institute, 1801 K Street, NH, Washington, DC 20006.
-------
SHORT FORM ADJUSTMENT PROCEDURE
FOR COMMERCIAL OIL-FIRED BOILERS
Burner service organizations may wish to develop short-form recommendations that
tie in with overall company policy, service training doctrine, experience of service
technicians and local regulations. The following is an example of a short form condensed
from the recommended procedure outlined in these Guidelines.
1. CLEAN &
SEAL
Clean burner and boiler heat-transfer surfaces. Seal air leaks.
2. SET OIL Be sure that oil is suitable for burner. For residual oil, adjust the
PREHEAT oil preheat temperature for proper pumping and atomization. If the fuel
viscosity is not known, start at 250 degree F preheat level. Then back
off to lower preheat temperature until best combustion is obtained.
3. ADJUST Adjust the atomizing pressure to manufacturer's recommendations and the
INPUT fuel input to meet full load demand.
4. SMOKE- Operate the oil burner at full load until up to temperature, using an air
COo setting for clean combustion. Take several readings of smoke and C02 as
needed to identify the C02 value above which the smoke starts to rise
rapidly.
5. ADJUST Adjust the air setting about 1/2 percent C02 lower than the point where
AIR smoke begins to rise sharply. Keep in mind that high C02 settings are
SETTING important for good thermal efficiency. Therefore, adjust for the highest
practical C02 level without excessive smoke. (Smoke number should not
exceed No. 4 when firing residual oil and No. 1 when firing distillate oil.)
6. DIAGNOSE If unable to adjust the burner to operate at acceptable smoke levels while
PROBLEMS maintaining at least 12 percent C02, it is likely that the atomization
and/or fuel-air mixing are poor. Check the air-handling parts, nozzle,
atomizing pressure, and preheat.
7. ADJUST Repeat adjustment procedure at low-fire setting and at an intermediate
CONTROL firing rate, by adjusting the air-fuel control linkage. Check several
LINKAGE points at intermediate firing rates throughout the range.
8. ADJUST For dual-fuel boilers, use a similar procedure to adjust for operation on
FOR GAS gas. C02 readings for gas will be somewhat lower than for oil. Check for
FIRING CO using a suitable CO detector, especially at the extremes of the air-
adjustment range. Verify oil settings.
9. CHECK Make sure ignition occurs promptly at light-off firing rate.
IGNITION
10. SCHEDULE Arrange the control system so that individual boilers avoid operation at
BOILERS low fire or at full load for extended periods. Avoid excessive on-off
cycling.
11. ANNUAL An annual tune-up and safety check is strongly recommended.
CHECKUP
Adjustment by these procedures will help to reduce air-pollutant emissions and also
achieve efficient fuel utilization. For additional details, see the corresponding steps on
pages 3-8 of these Guidelines.
-------
F-2 ____
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-76-088
2.
3. RECIPIENT'S ACCESSIOf+NO,
4. TITLE AND SUBTITLE Guidelines for Burner Adjustments of
Commercial Oil-Fired Boilers
5. REPORT DATE
March 1976
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
David W. Locklinand Richard E. Barrett
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Battelie-Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
10. PROGRAM ELEMENT NO.
1AB014; ROAP 21ADG-AM
11. CONTRACT/GRANT NO.
68-02-0251
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Guidelines; October 1975
14. SPONSORING AGENCY CODE
EPA-ORD
is. SUPPLEMENTARY NOTES Project officer for this document is R.E, Hall, Mail Drop 65^
Ext 2477. EPA-600/2-75-069-a was the first document of this series. The document
is available from the National Technical Information Service.
16. ABSTRACT
The Guidelines contain recommended oil-burner adjustment procedures
for commercial boilers to minimize air pollution and for efficient fuel use. They are
intended for use by skilled service technicians in adjusting commercial oil-fired
boilers, and as an aid to service managers engaged in training service technicians.
In addition to recommended steps for burner adjustment, the Guidelines include
appendixes of background material on pollutants of main concern, field-type
instruments and significance of measurements, fuel-oil grades, and emission
characteristics of commercial boilers.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Air Pollution; Space Heating; Combustion
Commercial Buildings; Burners; Boilers
Furnaces; Nitrogen Oxides; Nitrogen Ox-
ide (NO); Nitrogen Dioxide; Smoke
Carbon Monoxide; Hydrocarbons; Sulfur Ox
ides; Sulfur Dioxide: Natural Gas
Fuel Oil: Residual Oils
Air Pollution Control
Stationary Sources
Emission Factors
Particulate
Distillate Fuel Oil
Oils (No. 2,4,5, and 6)
13B ISA 21B
13M
07B
07C
2 ID 11H
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report I
Unclassified
21. NO. OF PAGES
29
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
------- |