EPA-340/1-83-023
Combustion Efficiency Optimization
Manual for Operators of Oil-
and Gas-Fired Boilers
by
PEDCo Environmental, Inc.
11499 Chester Road
Cincinnati, Ohio 45246
Contract No. 68-01-6310
Task Order No. 54
EPA Project Officers: Joseph R. Gearo, Jr.
Jerry Lappan
Prepared For
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air Quality Planning and Standards
Stationary Source Compliance Division
Washington, D.C. 20460
September 1983
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DISCLAIMER
This report was prepared by PEDCo Environmental, Inc., Cincinnati, Ohio,
under Contract No. 68-01-6310, Task Order No. 54. It has been reviewed by
the Stationary Source Compliance Division of the Office of Air Quality Plan-
ning and Standards, U.S. Environmental Protection Agency and approved for
publication. .Approval does not signify that the contents necessarily
reflect the views and policies of the U.S. Environmental Protection Agency.
Mention of trade names or commercial products is not intended to constitute
endorsement or recommendation for use.
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CONTENTS
Figures
1. Introduction
1.1 Purpose and general content
1.2 Organization
1.3 Use of the Manual
2. The Combustion Process
2.1 The combustion process and combustion chemistry
2.2 Requirements for complete combustion
3. Boiler Efficiency and Heat Losses
3.1 Heat losses - Fireside
3.2 Heat losses - Waterside
4. Boiler Efficiency Improvement
4.1 Checklists for pre-test inspection, correction, and
adjustment of boilers
4.2 Measurement, instrumentation, sampling point, and data
requirements for tuning/testing of boilers
4.3 Procedures for achieving low excess oxygen boiler operation
4.4 Burner adjustment
4.5 Maintaining low excess oxygen
5. Maintaining High Boiler Efficiency
5.1 Combustion efficiency spot check
5.2 Boiler operator's log and performance monitoring
5.3 Instrumentation and controls
5.4 Additional considerations in a boiler maintenance program
References
Page
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3
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7
12
15
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31
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34
35
36
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CONTENTS (continued)
Appendices
A Instrumentation for Flue Gas Measurements
B Illustrative Example - Use of Test Data from the Minimum
Oxygen Adjustment Procedure
C Combustion Efficiency
D Tracking Procedure for the Continuing Evaluation of
Boiler Performance
E Example Inspection/Maintenance Checklists
A-l
B-l
C-l
D-l
E-l
IV
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FIGURES
Number
1
2
3
4
B-.l
C-l
C-2
C-3
C-4
D-l
D-2
D-3
Variation in boiler efficiency losses with changes in
excess 02
Variation in boiler efficiency losses with changes in
boiler firing rate
Sample data sheet
Typical characteristic curves of smoke or CO versus 09 for
oil- and gas-fired boilers
Example data: carbon monoxide (ppm) versus oxygen (%)
Combustion efficiency as a function of stack gas
temperature and flue gas oxygen content for natural
gas firing
Combustion efficiency as a function of stack gas temper-
ature and flue gas oxygen content for No. 2 oil firing
Combustion efficiency as a function of stack gas temper-
ature and flue gas oxygen content for No. 6 oil firing
Comparative relationship between boiler excess air and flue
gas concentrations of oxygen and carbon dioxide when
burning oil or natural gas
Example of Boiler Fact Sheet
Example of Boiler Data Record Sheet
Example plots of Boiler Tracking Data
Page
10
11
21
24
B-2
C-2
C-3
C-4
C-5
D-3
D-4
D-6
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SECTION 1
INTRODUCTION
1.1 PURPOSE AND GENERAL CONTENT
This manual provides general guidance to operators of oil--and gas-fired
boilers to increase boiler efficiency, to improve fuel consumption, and to
reduce pollutant emissions. Boiler operating principles :and suggestions to
improve boiler performance are discussed. Combustion is explained in simple
terms. Various heat losses are described, and suggestions are given on means
to minimize or eliminate heat losses. The manual describes boiler adjustments
for peak operating efficiency, optimum fuel consumption, and reduced pollutant
emissions. Efficiency, fuel consumption, and emissions are all sensitive, to
many of the same boiler operating parameters. This manual describes feasible -
operating techniques and combustion adjustments to achieve clean, safe, and
efficient boiler operation.
1.2 ORGANIZATION
This manual consists of five sections. Section 2 is a simplified dis-
cussion of the combustion process to provide the boiler operator with a basic
understanding of the major factors that affect combustion efficiency. Major
topics in Section 2 are the combustion process, combustion chemistry, and
requirements for complete combustion. The combustion roles of excess air,
fuel-air ratio, and the three T's of combustion (time, temperature, and turbu-
lence) are briefly discussed.
Section 3 examines major heat losses and their effects on boiler effi-
ciency. This discussion, which covers both fireside and waterside losses,
explains where these losses occur and how they affect boiler efficiency.
Topics in Section 3 include dry flue gas, water vapor, fireside combustible
and radiation losses, water quality, blowdown, feedwater losses, and waterside
piping losses. The causes, effects, and prevention of these losses are also
included.
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Section 4 discusses various techniques for improving boiler efficiency,
focusing on minimizing stack gas heat loss by testing and adjusting the com-
bustion process for low-excess-oxygen firing. Pre-test inspection checklists
are included. These are useful in repairing the boiler equipment to its best
possible working condition as a preparatory step to the testing and adjusting
procedure. Measurement, instrumentation, and data requirements for testing
and adjusting are discussed. The general testing and adjustment procedure is
then explained, followed by a discussion of test preparation and test manage-
ment considerations. A step-by-step procedure to adjust the combustion air is
provided to assist operators in achieving improved boiler efficiency.
Section 5 discusses how to maintain high boiler efficiency once it has
been attained. Basic tools for monitoring boiler performance are discussed;
maintenance of a continuous boiler operator's log is emphasized. Instru-
mentation for boiler performance monitoring is presented, and suggestions are
made regarding data that should be routinely monitored and logged. This
section of the manual concludes with a brief discussion of a boiler main-
tenance program.
1.3 USE OF THE MANUAL
This manual provides simplified guidance to achieve clean, efficient
boiler operation. Because of its simplicity the manual has certain inherent
limitations so that caution in the use of the manual is required. Combustion
controls, burners, and other equipment vary widely in design, complexity,
operation, and sophistication. Simplification of information for a manual of
this nature does not permit a very detailed engineering discussion of all of
the specific equipment and boiler configurations that are available or in use.
Therefore, the guidance and procedures that are presented should only be used
in conjunction with available technical information and documents for the
specific boiler facility. This manual supplements but does not replace or
supersede the equipment manuals, handbooks, boiler codes, and other technical
documents that apply specifically to a particular boiler facility. Any con-
flicts between specific information for a boiler and the information in this
manual should be resolved before any suggested procedures are implemented.
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SECTION 2
THE COMBUSTION PROCESS
A boiler converts available fuel energy to usable energy in the form of
steam. The boiler operator's job is to operate the boiler safely and effi-
ciently to optimize the combustion and heat extraction processes and to mini-
mize the emission of air contaminants. An understanding of basic factors that
affect combustion is essential to safe, efficient boiler operation. This
section is a simplified discussion of the combustion process and the effects
of various combustion parameters on the boiler operation.
2.1 THE COMBUSTION PROCESS AND COMBUSTION CHEMISTRY '
The oxidation of an element or compound is generally accompanied by a°
release of heat energy. If oxidation occurs slowly, as in the tarnishing or
rusting of metals, heat is generated so slowly that it is lost to the sur-
roundings. On the other hand, combustion is a rapid oxidation process that
releases energy that can be harnessed to do useful work.
By volume, air consists of 21 percent oxygen, 78 percent nitrogen, and
trace amounts of other gases such as argon and carbon dioxide. By weight, air
is 23.2 percent oxygen and 75.5 percent nitrogen; approximately 4.32 pounds of
air are required to supply one pound of oxygen for combustion.
Most common fuels consist primarily of compounds that contain carbon and
hydrogen. These fuels react rapidly and readily with oxygen to produce heat.
Essentially, the hydrogen and carbon contents of the fuel determine its heat-
ing value. In the English system the unit of heat measurement is the British
Thermal Unit (Btu), defined as the heat energy required to raise the tempera-
ture of one pound of water from 59 to 60 degrees Fahrenheit at standard baro-
metric pressure.
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2.1.1 Combustion Chemistry
Oxygen combines with the fuel hydrogen and carbon in fixed proportions by
weight in accordance with the laws of chemistry. For example the combustion
of carbon in oxygen produces carbon dioxide and heat as follows:
12 pounds
02
32 pounds
CO,
Heat
44 pounds 169,800 Btu
This equation shows that complete combustion of one pound of carbon
requires 2.67 pounds of oxygen (about 11.5 pounds of air); the reaction will
also produce 3.67 pounds of carbon dioxide and 14,150 Btu's.
The equation for the combustion of hydrogen in oxygen is:
2 H2 + 02 -» 2 H20 + Heat
4 pounds 32 pounds 36 pounds 244,000 Btu
One pound of hydrogen requires 8 pounds of oxygen (34.6 pounds of air)
and produces 9 pounds of water and 61,000 Btu.
In the combustion of hydrogen-bearing fuels not all of the liberated heat
is recoverable. Since the combustion temperature is relatively high, the water
forms as a vapor, and latent heat energy is lost in the flue gas if this vapor
is not condensed to recover the vaporization energy. Thus, any fuel that
contains hydrogen has a higher heating value (HHV) and a lower heating value
(LHV) that differ by this energy of vaporization. For hydrogen combustion the
HHV is 61,000 Btu per pound of hydrogen; the LHV is 51,500 Btu per pound of
hydrogen. (For carbon the HHV and the LHV are the same since no water is
formed.) The HHV's for some common fuels are:
Bituminous (soft) coal
Anthracite (hard) coal
Number 2 oil
Number 6 oil
Natural gas
14,000 Btu/pound
12,700 Btu/pound
19,000 Btu/pound
18,100 Btu/pound
22,800 Btu/pound
(1000 Btu/cubic foot)
2.2 REQUIREMENTS FOR COMPLETE COMBUSTION
Four conditions affect the degree of combustion that will occur: fuel/
air ratio, turbulence, temperature, and time. The last three are commonly
called the three T's of combustion.
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2.2.1 Fuel/Air Ratio
The theoretical air requirement to burn any fuel completely can be calcu-
lated via combustion equations. This theoretical (stoichiometric) calculation
indicates the amount of air necessary to burn a fuel under ideal conditions,
leaving no unburned fuel and no uncombined oxygen. If an excess of fuel is
provided, not all fuel will be burned; combustion efficiency and heat output
will be reduced, and incomplete combustion will result in unburned fuel and
lost energy. For example, the incomplete combustion of carbon produces carbon
monoxide (CO) - an explosive and toxic gas. The reaction (2 C + 02 -> 2 CO)
releases only 30 percent (4350 Btu per pound of carbon) of the available heat
in the carbon, and the remaining 70 percent is lost. Incomplete combustion
will be accompanied by pollutant emissions (carbon monoxide, smoke, soot,
unburned fuel), wasted energy, and potential health and explosion hazards.
If too little fuel is provided the fuel/air mixture is lean (fuel-defi-
cient); boiler efficiency will be reduced because heat will be absorbed by
unused air that is discharged from the stack.
Excess Air—
In actual practice more than the stoichiometric amount of air is required
to ensure complete combustion. Excess air is necessary for several reasons.
One reason is that the mixing of fuel and air is not perfect; therefore, some
fuel fails to make contact with oxygen. Also the presence of nitrogen (air is
78 percent nitrogen) tends to inhibit fuel-oxygen contact. To overcome these
interferences excess air must be supplied with the fuel.
Excess air is a primary boiler operating variable and a major factor in
safe, efficient boiler operation. The required quantity of excess air for a
particular boiler depends on factors such as fuel type, fuel composition,
boiler design, firing rate, burner design, and burner adjustment. Since the
proper fuel/air ratio is a key to efficient boiler operation, the boiler
operator should strive to operate with only enough excess air to minimize
smoke, carbon monoxide, and unburned fuel.
2.2.2 Turbulence
The proper fuel/air ratio does not ensure complete combustion unless the
air and fuel are thoroughly mixed so that every fuel particle comes into
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contact with sufficient oxygen to burn it. Turbulence in the combustion zone
prevents rich and lean gases from stratifying, mixes the fuel with the air,
and promotes complete combustion.
2.2.3 Temperature
In addition to air and fuel, temperature must be adequate for combustion.
Each combustible substance has a specific ignition temperature and will not
burn until the fuel reaches that ignition temperature. Heat, usually from a
pilot flame, is required initially to raise the fuel temperature to its igni-
tion temperature, the temperature at which more heat is released by combustion
than is required to sustain ignition. Once ignition has occurred the excess
heat ignites surrounding fuel, and combustion continues until one of the three
requirements for combustion (heat, oxygen, or fuel) is absent or inadequate.
For example if the fuel is not all burned by the time the flame impinges on a
cooler surface (boiler tubes, shell or setting), the flame may be cooled below
the ignition temperature. Combustion will cease, and some fuel may fail to
burn.
2.2.4 Time
Combustion is not instantaneous; time is required to vaporize liquid fuel
(or to drive off volatiles from solid fuel), to mix combustibles with air, to
raise the fuel to its ignition temperature, and to burn the fuels completely
before they cool below ignition temperature. The required residence time for
combustible material in the boiler is tied closely to the boiler size, shape,
and design. There must be enough space in the boiler's high temperature zone
so that combustion is. complete before flame cooling occurs.
The three T's of combustion go hand in hand, and each affects the other.
Turbulence speeds up liquid fuel vaporization, fuel/air mixing, and contact.
Higher temperatures increase combustion rates, promote thermal turbulence and
mixing, and decrease the combustion time required.
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SECTION 3
BOILER EFFICIENCY AND HEAT LOSSES
It is a fundamental thermodynamic law that energy cannot be created nor
destroyed, but the form of the energy can be changed or converted to a differ-
ent form. As an example a change from chemical to thermal energy occurs
during a chemical oxidation (combustion) reaction but the energy quantity
before and after the reaction remains equal. As applied to a boiler this
means that the sum of all of the energies leaving the boiler (steam, radiant
heat, flue gas heat, and other energy forms) exactly equals the. energy in the
fuel burned. Stated another way:
Fuel energy = steam energy + miscellaneous heat and
. SJ other energy losses
"Boiler efficiency" is a measure of the thoroughness (or efficiency) with
which the boiler extracts the available heat energy from the fuel; it is the
percentage of fuel energy that is converted to useful heat energy (steam).
Stated another way:
Boiler efficiency = heat outPut -heat input - heat losses
heat input heat input
Since some heat loss is unavoidable, boiler efficiency is always less than 100
percent (boiler efficiency = 100% - heat losses).
Some heat losses can be minimized or eliminated by proper operating and
maintenance practices. Heat losses arise on the heat generation side (fire-
side) of the boiler and on the heat transfer-extraction side (waterside) of
the boiler.
3.1 HEAT LOSSES - FIRESIDE
Four major sources of heat loss on the fireside of the boiler are:
!• Dry flue gas loss - The heat carried out the stack by the hot flue
gases. This loss increases with higher stack temperatures and
larger amounts of excess air.
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2. Water vapor loss - Water vapor in the flue gas comes from the com-
bustion of hydrogen in the fuel and from moisture in the fuel and
combustion air. The heat absorbed in changing the fuel moisture to
vapor and the latent heat of the product moisture from combustion of
hydrogen are lost. This latent heat could be recovered by con-
densing out the water vapor from the flue gas, but this is- not prac-
tical because the lower flue gas temperatures necessary to condense
the water vapor would also condense acid vapors in the flue gas,
causing corrosion of exposed surfaces and reducing plume rise.
Therefore the latent heat of the water vapor is not considered to be
recoverable.
3. Combustible loss - The combustible loss consists of all combustible
material carried away in the flue gas and includes unburned fuel and
the products of incomplete combustion. Maladjusted burners and
equipment can cause excessive combustible losses.
4. Radiation loss - This heat loss is the heat that radiates through
the boiler walls to the boiler room. This loss is fairly constant
at all firing rates. Inadequate or deteriorated insulation and
furnace wall refractory material increase these losses.
The dry flue gas, water vapor, and combustible losses are all energy
losses that leave the boiler through the stack. Stack gas heat loss, the sum
of these losses, is the largest single source of lost energy in a boiler; the
greatest improvements in boiler efficiency can be gained by minimizing this
loss. The magnitude of this loss depends on the temperature and flow of gases
leaving the boiler; reductions in either will reduce heat loss and increase
boiler efficiency. There are three basic methods of minimizing stack gas heat
loss:
1. Use flue gas heat recovery equipment.
2. Maintain clean heat transfer surfaces.
3. Minimize excess air.
Heat recovery equipment such as a combustion air heater or an economizer
extracts usable heat so that it is not lost out the stack. An engineering
study for each specific boiler is required to determine if such devices are
suitable and cost effective.
Soot build-up and slagging on boiler tubes insulates the tubes from the
furnace heat and results in decreased heat transfer. As a consequence the
flue gas temperature increases, boiler efficiency decreases and the boiler
firing rate must be increased in order to maintain a given steam rate. An
8
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excessive build-up of soot on the boiler tubes can lead to: (1) plugging of
gas passages between tubes, upsets in boiler water circulation, increased
draft loss, and increased fan horsepower requirements; (2) absorption of
acid-bearing moisture and corrosion of tube surfaces on the fireside; and
(3) metal stress due to high flue gas temperatures, leading to tube leaks and
equipment failure.
Firing with minimal excess air decreases stack gas heat loss by reducing
flue gas flow and lowering gas velocity through the boiler. As a result
boiler tube surfaces are in contact with the hot flue gases longer (increased
residence time), and heat can be more thoroughly absorbed. The longer resi-
dence time also promotes complete combustion. Thus, the direct result of low
excess air firing is improved combustion, lower flue gas temperature and flow,.
reduced stack gas heat loss and increased boiler efficiency. Conversely,
large quantities of excess air require more fuel to generate a given quantity
of steam. With excess air extra fuel must be burned to heat the unneeded air,
greater amounts of air and combustion gas pass through the boiler, gas veloc-
ity increases, residence time decreases, stack temperatures generally rise,
stack gas heat loss increases, and boiler efficiency falls. As a rule of
thumb boiler efficiency can be increased one percent for each 1.3 percent
reduction in oxygen (15 percent reduction in excess air> or for each 40 degree
reduction in stack gas temperature. Figure 1 illustrates the effects of
changes in excess oxygen on fireside efficiency losses.
Boiler efficiency also depends on the boiler firing rate; significant
changes in efficiency occur as the firing rate varies to meet load demand. At
low firing rates the radiation loss through boiler walls becomes an increas-
ingly higher percentage of the total heat losses. At higher firing rates the
dry flue gas loss increases, generally resulting in higher flue gas tempera-
tures. Figure 2 illustrates how the various efficiency losses are affected by
firing rate. For many industrial boilers the highest efficiencies (lowest
losses) occur within a firing rate range from approximately 50 to 80 percent
of capacity. Obviously, boiler operation in this range is advantageous.
Each boiler has an operating point of maximum efficiency. This is very
important at multi-boiler installations, particularly when there are demand
fluctuations. For maximum overall efficiency the load should be met by oper-
ating units at or near their maximum efficiency points. For example, good
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25
20
-15
in
in
O
O)
10
«*-
LU
Total efficiency loss
Flue moisture
Dry flue gas
Radiation
Combustibles (carbon monoxide)
2 3
Excess O. "/«
Figure 1. Variation in boiler efficiency losses
with changes in excess 02 (Reference 8).
10
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30
25
20
Total efficiency loss
.1/5
O)
CO
1/5
O
u
c
Q)
O
4-
UJ
15
10
5 -
Flue moisture
Combustibles (carbon monoxi
20 415 5tT
Percent of rated capacity
80
100
Figure 2. Variation in boiler efficiency losses
with changes in boiler firing rate (Reference 8).
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load management may require regulating one boiler to meet changes in steam
demand while operating all of the others at their individual maximum efficien-
cies. In order to practice good load management and to achieve maximum boiler
plant efficiency the efficiency curves for each boiler must be known, and the
points of maximum efficiency must be identified. With this information boiler
operators can make appropriate adjustments as some boilers are placed on-line
and others are removed.
Other fireside losses result from air infiltration and excessive soot
blowing. Air leakage into the boiler cools surfaces and necessitates a higher'
firing rate to compensate for this heat loss. The infiltrated air usually
does not help combustion and gives an erroneously high excess air reading at
the boiler outlet. This higher reading may be mistakenly interpreted as an
indicator of poor burner performance. Air leakage is most prevalent on older
balanced draft units. Most modern balanced draft units are built similar to
pressurized units and are less likely to have air leakage problems. Leaks on
pressurized units are outward and readily apparent. Escaping gas from such
units not only damages casings and insulation but also constitutes a hazard to
boiler room personnel.
Soot blowing schedules should be based on need rather than on an arbi-
trary basis. Each blower should be set to a minimum blow pressure and cycle
consistent with effective cleaning.
3.2 HEAT LOSSES - WATERSIDE
Factors that affect boiler waterside heat losses include:
1) Waterside cleanliness
2) Slowdown schedules
3) Feedwater temperature
4) Water level
5) Piping system
Waterside Cleanliness
The service water supply may contain calcium and magnesium minerals that
precipitate as scale on the heat transfer surfaces in the boiler. This scale
formation restricts heat flow so that an increased firing rate is required in
order to maintain a given steam rate. Thus, boiler efficiency decreases.
Boiler metal deterioration and corrosion also occur, due to elevated metal
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temperatures. Waterside cleanliness can be maintained by proper water treat-
ment and periodic chemical or mechanical cleaning of tube surfaces. Proper
water conditioning helps to prevent:
0 Corrosion - by maintaining the alkalinity of boiler water at a level
(usually at a pH of 10.5 to 11.5) that will neutralize acids and
prevent boiler metal attack.
0 Pitting due to dissolved oxygen in the water - by deaeration and/or
addition of chemicals such as sodium sulfite.
0 Hard scale - by use of chemical additives (usually sodium phosphate)
to intercept the hardness minerals or by treatment in water soften-
ing equipment.
0 Sludge deposition that might block tubes, upset water circulation or
impair heat transfer. In some cases external filtering and settling
may be desirable or necessary. Addition of organic sludge condi-
tioners to boiler water keeps the sludge in suspension for easier
blowdown and removal.
0 Foaming and carry-over caused by impurities in the water.
0 Caustic embrittlenient and weakening of boiler steel due to long
exposure to a combination of stress and highly alkaline water.
Since varying amounts of hardness minerals are found in almost all water
supplies, every boiler plant should have a water treatment specialist avail-
able to provide water testing services and to give advice on treatment methods
and chemical additives. By intercepting, changing, or neutralizing the hard-
ness minerals and maintaining proper water conditions, adverse effects of
waterside scale and corrosion on boiler performance can be minimized, and
equipment life and reliability can be enhanced.
Blowdown
Blowdown is used to remove water impurities that can cause scale de-
posits, priming, foaming, and caustic embrittlement of metal parts. Blowdown
water heat losses and the cost of treated boiler water that is wasted can be
substantial if the amount of blowdown is excessive. The required quantity of
blowdown water depends on the boiler and on make-up water quality. In some
cases the potential recovery of energy from the blowdown water may be sub-
stantial. Much of the blowdown heat energy can be reclaimed by using heat
exchangers to preheat make-up water.
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Feedwater Temperature
The temperature of water entering the boiler and,the water level in the
boiler are two important parameters that affect boiler operation. Higher
feedwater temperatures require less fuel to convert water to steam. Heat
recovery from boiler blowdown and from condensate streams can be effectively
used to raise water temperatures and thus provide fuel savings. An approxi-
mate one'percent fuel savings results for every 10°F rise in feedwater temper-
ature.'
Water Level
Maintaining the water level in the boiler is the most important safety
related function performed by the boiler operator. If the water level falls
too low heat transfer surfaces can be exposed, and subsequent damage can
result. On the other hand, large load swings in a boiler with a high water
level can result in water carryover into steam lines, causing water hammer and
potential damage.
Piping System
Heat loss from the piping system after the steam leaves the boiler in-
creases the fuel requirement on the boiler. Considerable heat energy is
wasted if steam and condensate lines are not insulated or if insulation is
allowed to deteriorate. Leaking pipes, fittings, and steam traps incur addi-
tional losses.
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SECTION 4
BOILER EFFICIENCY IMPROVEMENT
The most significant improvements in boiler efficiency can be obtained by
minimizing stack gas heat loss, primarily by reducing the flow and temperature
of gases passing from the boiler. The lowest stack losses-are achieved when
the boiler is tuned to use the least possible amount of excess air consistent
with efficient combustion of fuel. Although even a boiler in relatively poor
operating condition can be tuned to improve its efficiency and emissions,
improvements can be substantially greater if all boiler equipment is in proper
repair. Deficiencies discovered during the pre-tuning inspection may not be
correctable while the boiler is in service. Problems should be corrected, if
possible, before tuning adjustments are made; others should be placed on a
maintenance list for correction at the first boiler outage.
4.1 CHECKLISTS FOR PRE-TEST INSPECTION, CORRECTION, AND ADJUSTMENT OF BOILERS
Checklists for the more common items that require attention during the
pre-tuning inspection are shown below. These checklists provide a starting
point for the boiler operator to use in developing an assessment that is
specifically tailored to his boiler facility. The boiler manufacturer's
operating and maintenance manual should also be used in conjunction with these
checklists to prepare the boiler for tuning and optimization.
4.1.1 Oil Burner Checklist
Inspect to determine that:
0 Oil is at the proper temperature for pumping and good atomization
(too low or too high preheat temperature can cause poor combustion).
0 Atomizer is of proper design and capacity for oil type and burner
configuration (a mix-up can occur when tips that have been removed
for bench cleaning are reinstalled).
0 Oil tip passages and orifices are free of excess corrosion and
deposits (poor oil spray pattern can result).
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0 Burner diffusers are in good condition (not burned or broken), and
are located properly with respect to oil gun tip.
0 Oil gun is positioned correctly in burner throat.
0 Burner throat refractory is intact and undamaged.
0 Oil strainers are in place and clean.
4.1.2 Gas Burner Checklist
Inspect to determine that:
0 Filter and moisture traps are clean, in place, and operating to
prevent the plugging of gas orifices.
0 Injection orifices and passages are clear, clean, and free of ob-
structions.
0 Diffusers are located and oriented properly.
0 All burner parts are undamaged and in proper position.
4.1.3 Combustion Control Checklist
Inspect to determine that:
0 All safety lock and trip circuits are operable (burner controls,
feed-pump control, low water cut-off, safety relief valve, flame
monitoring systems, fuel shut-off valves, etc.).
0 Control linkages operate properly without excess play.
0 Fuel supply inlet pressures to all pressure regulators are suffi-
cient to assure constant outlet pressures at all firing rates.
0 Pilot and electrodes are clean and adjusted satisfactorily, and
electrical signals from pilot flame are proper.
0 All fuel valves are internally clean and have proper movement.
0 All gauges and metering devices are calibrated and functioning
properly.
4.1.4 Boiler Fireside Checklist
Inspect to determine that:
0 Tube surfaces are free of excessive deposits and fouling.
0 Soot blowers are aligned and operating properly.
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0 Gas passages and baffles are intact, clear, and free of leaks or
bypass.
0 Refractory surfaces and external insulation are intact and in good
condition.
0 Inspection ports are clean and operable.
0 Casing, breeching, ductwork, and stack are intact and leak-free.
4.1.5 Boiler Waterside Checklist
Inspect to determine that:
0 Water treatment equipment is operating properly.
0 Piping system, including the pipe and fittings, safety-release valve
vent, water column, blowdown valve, and steam traps are all free of
leaks, corrosion, and damaged insulation.
4.1.6 Flame Inspection
Observation of the flame can help to indicate combustion conditions in
the furnace chamber. A good flame is difficult to specify, since there are
wide variations in burner design that affect flame pattern and appearance.
Also, a certain amount of operator preference for a particular flame pattern
may be involved. However, flames under Tow and high excess oxygen firing
conditions do have some marked differences. Typically, the difference between
low and high excess oxygen firing may include the following:
0 Low excess oxygen firing produces a hazy and rolling flame that
grows in volume and more completely fills the furnace chamber as it
flows somewhat slowly through the furnace.
0 Oil firing with low excess oxygen produces a flame that is darker
yellow or orange. It may appear partially hazy.
0 Gas firing with low excess oxygen produces a flame that is more
luminous with yellow or slightly hazy portions.
0 High excess oxygen firing produces a flame that is intense, highly
turbulent and somewhat compact in appearance.
0 Oil firing with high excess oxygen produces a flame that is short,
bright and crisp. The flame may be somewhat unstable and may lift
away from the burner tip.
0 Gas firing with high excess oxygen produces a flame that is compact,
hard and bluish-white. The flame may be unstable, lift away from
the burner and may have a noticeable roaring noise.
17
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The flame appearance should be checked against the flame color, type, and
shape recommended by the burner manufacturer and corrected if necessary for
low oxygen firing. Pre-tuning adjustment by>an experienced boiler operator
will minimize the number of changes necessary during subsequent tuning and
testing.
The pre-tuning inspection of combustion conditions should include checks
to ensure that:
0 The flame does not impinge on any heat transfer surfaces.
0 The flame is not distorted (particularly in oil-fired units), which
would indicate an obstruction in the orifice or nozzle.
0 For oil firing, there are no stars or streaks in the flame.
0 There are no odors at the damper, diverter, or observation ports
that could indicate poor combustion or insufficient draft.
4.2 MEASUREMENT, INSTRUMENTATION, SAMPLING POINT, AND DATA REQUIREMENTS FOR
TUNING/TESTING OF BOILERS
The purpose of the inspection and adjustments discussed in Section 4.1 is
to place the boiler in the best possible condition for tuning. The purpose of
the optimization tests and attendant boiler tuning is to achieve maximum
boiler efficiency, and in so doing to establish performance and measurement
standards that reflect efficient operation. Routine spot checks and combus-
tion quality measurements can then be compared with established standards to
maintain high boiler efficiency and to detect any deterioration in perform-
ance. Frequent spot checks reduce the likelihood that a condition will de-
teriorate to the point that significant fuel waste and increased air pollution
result.
4.2.1 Measurements
Tuning a boiler for low excess oxygen conditions requires three basic
measurements:
0 Oxygen or carbon dioxide concentration to determine the level of
excess air.
0 Carbon monoxide to determine the minimum excess air requirement for
complete combustion. Stack opacity measurements are also useful in
detecting incomplete combustion, particularly for oil-fired boilers.
0 Stack gas temperature to determine the stack gas loss.
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The measurement of oxygen rather than carbon dioxide to determine excess air
is preferred because:
0 The relationship between oxygen and excess air is not greatly af-
fected by fuel composition. Carbon dioxide is a product of combus-
tion, and the quantity in the flue gas is dependent on the carbon
content of the fuel. Oxygen measurement, on the other hand, is more
representative of excess air conditions and is relatively unaffected
by the fuel used. ,
0 Instruments for oxygen measurements are generally more reliable and
less expensive than those for carbon dioxide. Also, the measurement
of carbon dioxide requires much greater precision than oxygen mea-
surement for the same relative degree of accuracy.
4.2.2 Instrumentation • • • . .
Portable electronic and chemical analyzers can be used for making the
oxygen or carbon dioxide and carbon monoxide measurements if the boiler is not
equipped with built-in analyzers. Hand-held chemical-absorbing and length-of-
stain (color indicator tube) analyzers provide reasonable accuracies when
operated by trained technicians using fresh chemicals. Electronic instruments
provide high accuracy, require no chemicals, and are available as portable or
panel-mounted instruments. A smoke tester and shade scale is useful in evalu-
ating smoke density from oil-fired boilers. A measured sample of flue gas is
withdrawn from the stack through a filter paper and the smoke spots are com-
pared with a standard smoke shade scale. Temperature measurements can be made
with stem or dial thermometers or other temperature sensors inserted in the
stack.
All chemicals and materials should be fresh, and all instruments should
be clean, in good repair, and properly calibrated to provide meaningful read-
ings. Additional information on instrumentation is provided in Appendix A.
4.2.3 Sampling (Measurement) Points
The measurement point location must be chosen with extreme care to ensure
a representative measurement. Flue gas samples for oxygen and carbon monoxide
measurement are especially sensitive to the sampling probe location. Air
leakage into ductwork and air preheaters dilutes the gases and gives false
indications of furnace conditions. The sampling location should be upstream
of the air preheater and any other known leaks.
19
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Gas streams immediately downstream of bends, dampers, or induced-draft
fans should be avoided since gases can stratify and give erroneous readings.
When a single-point sampling probe is used, several points in the duct should
be trial-sampled to find a representative location.
Flue gas temperature measurement is also subject to stratification error;
thus, a representative location must be selected. Since heat is lost from the
flue gas as it passes through the ductwork and stack, the temperature probe
should be located near the boiler outlet to obtain better readings.
4.2.4 Other Measurement Data
In addition to the key measurements discussed above, additional data are
necessary to provide a permanent record of boiler operation at the time of
boiler optimization and tuning. All data pertinent to boiler operating condi-
tions and stack measurements should be recorded to document boiler efficiency
and emission characteristics and to enable future comparisons for the diag-
nosis of any efficiency or emission problems. Suggested items to be recorded
on the prepared data sheet include:
0 Boiler identification and fuel used including percent sulfur and
fuel grade, test date, and operating personnel
0 Steam, feedwater, and fuel conditions (flow rates, pressures, and
temperature) to define boiler firing rate and steam generation
0 Position of combustion controls and burner settings
0 Furnace pressures, temperatures, and damper settings
0 Stack measurements (oxygen, carbon monoxide, and temperature) and
smoke measurements or observations. Location and position of sample
(noted or indicated on a dimensioned sketch)
0 Any changes that were made to combustion control or burner settings
and any relevant comments on observations of flame appearance or
furnace conditions
Figure 3 shows the format of a sample data sheet. Additions or deletions
can be made to fit a particular installation; the actual readings to be in-
cluded will depend on available instrumentation. The data sheet should in-
clude all necessary items to define exact boiler operating conditions for
future comparisons.
20
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Boiler No.:
Date:
Operator:
Fuel: Type/grade:
Heating valve:
Analysis:
Test No.
Steam flow rate
Steam temperature
Fuel flow rate
Fuel pressure
Fuel temperature
Combustion air temperature
Flue gas temperature
Furnace pressure
Stack pressure
Windbox pressure
Feedwater temperature
Fan settings
Air register settings
Burner positions
Firing rate
Smoke No.
*C02 in flue gas and/or
*02 in flue gas
Flame appearance:
Notes:
*Either or both C02 and 02 can be measured.
Figure 3. Sample data sheet.
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4.3 PROCEDURES FOR ACHIEVING LOW EXCESS OXYGEN BOILER OPERATION
Under ideal conditions, the minimum oxygen concentration required for
fuel combustion is dictated by balanced combustion chemistry equations.
However, excess oxygen is required in all practical cases to improve combus-
tion and to allow for variations in combustion controls, fuel properties,
atmospheric conditions, and other factors. As excess air is decreased, the
oxygen level drops until there is no longer enough oxygen for complete combus-
tion. At this point, there is a relatively rapid increase in unburned fuel
and carbon monoxide. This point is commonly called the minimum oxygen level,
the smoke limit, or the carbon monoxide limit. Peak boiler efficiency will
occur at or close to this level. Unfortunately, operation at this point
requires highly sophisticated combustion controls and flame quality monitoring
to prevent small changes that could result in unacceptable combustion condi-
tions. Some margin or operating criterion above the minimum oxygen level will
be necessary so that normal swings in load and other changes do not produce
undesirable conditions. This safety margin depends on load stability and
combustion control sophistication. This section presents procedures for
determining the lowest practical oxygen level for a particular boiler.
4.3.1 General Procedure
The general procedure for determining the lowest practical oxygen level
consists of a test series that establishes the following:
0 The initial conditions, i.e., before the oxygen level is adjusted.
0 The minimum oxygen level.
0 The lowest practical oxygen level where the boiler can be routinely
operated, i.e., at an oxygen level that incorporates an adequate
operating or safety margin above the minimum level.
0 The lowest excess oxygen level that is acceptable during load changes
that may occur during normal daily operation.
The minimum oxygen level will be determined by raising the excess oxygen
level to one or two percent above the existing level and then reducing the
excess oxygen in small steps until smoke begins to appear in the case of oil
firing, or carbon monoxide emissions rise above 400 parts per million (ppm) in
22
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the case of gas firing. For oil firing, the smoke limit rather than the
carbon monoxide limit is used to define the minimum oxygen level, since smoke
will generally appear before carbon monoxide emissions rise significantly.
The smoke limit for oil firing is the lowest possible excess oxygen level for
acceptable stack conditions. Acceptable stack conditions in terms of the
Bacharach Smoke Spot Number (SSN) for commonly used oil grades are: less than
one for No. 2 oil and four or less for residual (No. 6) oil.
Smoke and carbon monoxide readings should be taken at each oxygen level
and plotted to correlate the three variables. Figure 4 illustrates the dif-
ferent extremes that may result; a gradual increase (Curve 1) or a rapid
•increase (Curve 2) in smoke or carbon monoxide as the minimum oxygen level is
approached. If the curve is steep (as in Curve 2), small changes in excess
oxygen can result in excessive smoke and carbon monoxide levels and potential-
ly unstable conditions. Therefore, extreme caution is required when changes
are made near the smoke limit. In all cases, oxygen levels should .be altered
in very small steps when approaching the smoke limit until the data show
whether the curve is gradual or steep. It is also extremely important to
remember that a boiler may have a gradual smoke/carbon monoxide characteristic
at one firing rate and a steep one at another.
The experimentally-determined minimum oxygen level should be compared
with the manufacturer-recommended level for the test firing rate, since a
comparatively high oxygen level may indicate problems due to equipment mal-
functions or maladjustments. Such problems should be corrected before oxygen
optimization is attempted. Such problems can usually be avoided if the pre-
tuning inspection and correction procedures suggested in Subsection 4.1 are
followed. A range of acceptable minimum excess oxygen levels is difficult to
specify because different burner designs and fuels have different excess
oxygen requirements. Reference 8 suggests that the minimum excess oxygen at
high firing rates ranges from 0.5 to 3.0 percent for natural gas and from 2.0
to 4.0 percent for oil.
After the minimum oxygen level is established, the next step is to deter-
mine the appropriate oxygen margin or operating "cushion" above the minimum
where the boiler can be operated routinely, i.e., the lowest practical oxygen
level for the boiler. This operating margin is necessary in order to accommo-
date the following:
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Low excess Op settings
High excess 02 settings
•Curve 2
Curve 1
CO limit (400 ppm) o
smoke limit
Minimum Oo -'
-Operating margin above
minimum 0,
Automatic controls
are adjusted to this
0,
PERCENT 02 IN FLUE GAS
Curve 1 - Gradual smoke or CO vs. 02 characteristic
Curve 2 - Steep smoke or CO vs. 02 characteristic
Figure 4. Typical characteristic curves of smoke or
CO versus 02 for oil- and gas-fired boilers.
24
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Rapid load swings that can cause incomplete combustion if an ade-
quate margin is not provided.
Non-repeatability or normal play in automatic controls. (Poor repeat-
ability or excessive play can be determined by repeating a firing
rate from both the high and low sides while allowing fuel and air
controls to function normally and then comparing excess oxygen
levels after the boiler is stabilized. Excess oxygen should repeat
within a few tenths of a percent. Excessive play suggests inspec-
tion of the control system for tolerance problems in air dampers,
control shafts, valve cams, controllers, etc., and correction of any
problems that are discovered.)
Normal variations in atmospheric conditions. (For boilers not equipped
with temperature/pressure compensation systems, extreme variations
in atmospheric conditions can cause excess oxygen changes of one
percent or more.)
Fluctuations in fuel properties that modify excess oxygen require-
ments.
Typical margins above the minimum oxygen level may range from 0.5 to 2.0
percent, depending on the control system and fuel characteristics at a par-
ticular boiler (Reference 8).
Lowest practical oxygen determinations should be made for several boiler
firing rates. The optimum excess oxygen level should be determined at several
firing rates within the boiler's operating range. A sufficient number of
determinations at different firing rates should be made to assure that after
the final control adjustments are made, the optimum oxygen conditions are
maintained at all intermediate firing rates. Some compromise may be necessary
to select a final oxygen level that gives good performance over a range of
firing rates. If the boiler is used at only one particular firing rate, it
should be set to optimize conditions at that rate.
4-3.2 Test Preparation and Management Considerations
Pre-test planning and preparation ensures that the optimization tests and
adjustments proceed smoothly and produce meaningful results. A test plan
should be developed which outlines the procedures, participants, boiler opera-
ting and test conditions.
Advance planning and preparation should address the following:
0 Manpower requirements. Sufficient personnel must be available to
continuously monitor controls, instrumentation, flame appearance,
and stack conditions during adjustments so that simultaneous data
measurements can be made.
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0 Instruction. All participants should be instructed in advance
regarding the test purpose and the respective roles of each partici-
pant during the test.
0 Instrumentation. All required instruments and metering devices
should be checked for proper operation well in advance of each test
so that necessary parts replacement and repair can be completed.
Instruments, etc. should then be calibrated and tested.
0 Test measurements and data records. The optimization procedure
focuses on the measurement of incremental changes in firing condi-
tions due to changes in the oxygen supply to the boiler. Accord-
ingly, proper measurements are necessary to produce meaningful test
results. Monitoring personnel should be given pre-test instruction
which stresses the importance of proper timing and technique in
"making and recording test measurements, readings, and observations.
Personnel should be instructed to record the data only during stable
boiler conditions and to make all readings and observations simul-
taneously (on command). Additionally, data record forms should be
prepared in advance and personnel instructed in their use and pur-
pose.
0 Boiler manuals. The operation and maintenance manuals for the
boiler and boiler equipment should be assembled, and pertinent sec-
tions should be marked for quick reference during the boiler tuning/
adjustment. The manuals should be reviewed for apparent conflicts
with the adjustment procedures outlined below. Such issues should
be resolved before starting these procedures.
0 Steam service disruption. The firing rate will usually be con-
trolled manually during the tests to obtain stable conditions and
constant steam pressures. Depending on the firing rate, the quan-
tity of steam generated may be more or less than the steam demand.
Where other boilers are available, the loads on those boilers should
be modulated to meet system demand. Otherwise, prior arrangement
and planning are necessary so that excess steam can be dumped during
high firing conditions and/or steam service can temporarily be
disrupted during low firing conditions.
4.3.3 Safety Related Considerations
The step-by-step procedures presented here are generally applicable to
low excess oxygen firing of oil- and gas-fired boilers. However, combustion
controls, burners and other furnace and boiler equipment vary widely in
design, complexity, and capacity. Therefore, it is recommended that the
procedures be supplemented by and be used in conjunction with technical docu-
ments such as local/national boiler safety codes, air pollution regulations,
operation/maintenance manuals, and other documents supplied by boiler equip-
ment manufacturers. These documents should be examined and compared with the
suggested procedures and any apparent conflict between codes, boiler equipment
26
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manuals, and the guideline procedures should be resolved before the procedures
are implemented. The procedures should be modified as necessary to accommo-
date any special facility requirements and both the procedures and test plan
should be specifically tailored to the facility.
It is emphasized that the optimization procedures are not intended to
replace or supercede any procedures or requirements that are necessary for
safety reasons. Manufacturers' recommendations should be followed and local
and national boiler safety codes must be observed at all times. Safety must
never be compromised in boiler operation and it is therefore appropriate to
stress the safety aspects of implementing low excess oxygen operation.
Safety and the Optimization Procedure .
With the boiler in good operational condition and all pre-test planning
and preparation completed, the tests and adjustments to achieve low excess
oxygen firing can begin. Caution is the key word in applying this or any
other combustion modification procedure.
Pre-Test Safety Checks—
Immediately prior to initiating the procedure, checks and observations
should be made to ensure that:
0 All boiler safety interlocks and trip circuits are operable and
functioning properly.
0 Pilot lights and electrodes are adjusted satisfactorily.
0 Fuel pressures and boiler water levels are within acceptable opera-
ting ranges.
0 Flame color and shape indicate satisfactory combustion conditions.
0 Boiler operation and firing conditions are stable.
Safe Conduct of the Optimization Procedure—
During the oxygen optimization procedure:
0 Know at all times the impact of any adjustments on fuel flow, air
flow, or the control system.
0 Be alert for any changes in boiler settings or changes in fuel
pressures/properties that might affect the flow of air or fuel to
the burner and produce uncontrolled shifts in excess oxygen.
0 Exercise-extreme caution when making oxygen changes near the smoke
or CO limit. Do so in very small steps. As the minimum oxygen
27
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condition is approached and/or reached, unpredictable and potentially
unstable conditions can occur with small oxygen changes. For pur-
poses of testing, occasional CO levels of up to 1000 or 2000 ppm can
be acceptable provided adequate and attentive boiler monitoring and
flame observation is made to assure stable conditions. Further
reduction of the excess oxygen results in very rapid increases in CO
and other combustibles which can lead to flame instability, furnace
pulsation, and boiler explosions. Remember, a boiler may exhibit a
gradual change at one firing rate and have a rapid change at another.
Control system adjustments while operating at low loads is not
recommended. Air flow requirements at low-fire conditions usually
are dictated by flame ignition characteristics and stability rather
than by combustion efficiency.
Do not reduce air flow by throttling the burner air registers.
alters the fuel/air mixing characteristics and complicates the
tests.
This
0 Observe and maintain the proper water level in the boiler. If the
water level falls too low, heat transfer surfaces can be exposed and
boiler explosions or other damage can result.
0 Watch boiler instrumentation closely while making any changes and
frequently observe the flame appearance as an indicator of combus-
tion conditions.
4.3.4 Step-by-Step Procedure for Low Excess Oxygen Operation (Reference 8)
1. Operate the boiler at the desired firing rate with combustion con-
trols in the manual mode. Make sure that all safety interlocks are still
functioning. Mark the linkage setting in order to retrace the direction and
position of the adjustments.
2. After the boiler has stabilized, observe flame conditions and take a
complete set of boiler and stack readings. This will establish the existing
operating conditions at the particular firing rate. If the excess oxygen is
close to the lower end of the range of typical minimum oxygen values (Section
4.3.1), and if carbon monoxide and smoke are at acceptable levels, it is quite
possible that the boiler is already operating near the optimum excess oxygen
at this particular firing rate. It may still be desirable to proceed through
the following steps to determine whether lower excess oxygen levels are prac-
tical. In any event, do not assume that oxygen settings at other firing rates
are also close to the optimum.
3. Increase excess air until the stack excess oxygen has increased by
one or two percent. Take readings after the boiler has stabilized and note
any changes in flame conditions.
28
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4. Return excess air to the normal level and then slowly reduce the
excess air in small steps. Watch the stack for smoke, and constantly observe
the flame. Take a set of stack readings following each change. Watch out for
low windbox/furnace pressure emergency shutdown safety interlocks ("fuel trip"
set points) at low firing rates.
5. Continue to reduce the excess air stepwise until one of the follow-
ing limitations is encountered.
0 Unacceptable flame conditions such as flame instability or flame
impingement on furnace walls.
0 High carbon monoxide content in the flue gas. In normal operation
the carbon monoxide should not exceed 400 ppm, but levels up to 2000
parts per million are tolerable during the test. . Use caution since
carbon monoxide can increase very rapidly with small changes in
excess air.
0 Smoke. Do not confuse smoke with water vapor, sulfur, or dust
plumes which are usually white or gray in appearance. Smoke spot
readings should be less than one for No. 2 oil and less than four
for No. 6 oil or coal.
0 Equipment related limitations such as low windbox/furnace pressures
or built-in air flow limits.
6. Obtain carbon monoxide, oxygen, and smoke readings to establish
curves similar to the samples shown previously in Figure 4. Plot the data on
graph paper.
7. The minimum excess oxygen requirement for the boiler was determined
in Step 6, but do not adjust the burner controls to this value. Although this
may be the point of maximum efficiency, it is probably impractical to operate
the boiler right on the combustible or smoke threshold.
Compare the minimum oxygen requirement to the value recommended by the
.boiler manufacturer. Typical values for various fuels are given in Section
4.3.1. If the minimum oxygen requirement is substantially higher than the
manufacturer recomendation, further burner adjustments may allow operation at
lower oxygen levels.
8. Establish an excess oxygen margin to accommodate fuel variations,
load changes, and atmospheric conditions. Reset the burner controls to main-
tain this excess oxygen when operating in the automatic control mode.
This is the lowest practical excess oxygen for the boiler at a particular
firing rate. The boiler efficiency at this condition is as close as practical
to peak efficiency, which usually occurs near the minimum excess oxygen.
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9. Repeat Steps 1 through 8 for each firing rate to be tested. For
some control systems it will not be possible to set the optimum excess oxygen
at each firing rate since control adjustments at one firing rate may also
affect conditions at other firing rates. In this case, use judgment to select
a setting that gives good performance throughout the range of firing rates.
Repeated tests may be necessary. If the boiler is operated at one predominant
firing rate, the setting should be made to optimize conditions at that rate,
allowing for acceptable firing at other rates.
10. After the control adjustments have been completed, verify that the
new settings will be acceptable during all load changes that may occur. While
making rapid load swings, observe the flame and stack to preclude any unac-
ceptable conditions. Utilize stack continuous monitors (oxygen, carbon mon-
oxide, opacity) when available. If undesirable conditions are detected, reset
the combustion controls to provide slightly more oxygen at the particular
firing rates. Verify these new settings in a similar fashion. Document the
selected control settings for future reference.
11. Adjustments at or near low-fire conditions may not be advisable.
Excess air requirements at these conditions are usually dictated by flame
ignition characteristics and stability which can be critical and difficult to
evaluate.
12. When an alternate fuel is fired, perform the above tests and adjust-
ments for the second fuel. In some cases it may not be possible to achieve
optimum combustion of both fuels at all firing rates. In these cases, a
compromise must be made, and judgment must be used to select the best condi-
tions for normal firing rates.
Appendix B shows by example how the data obtained from the above proce-
dures are used to define the lowest practical oxygen level for safe, efficient
combustion. Appendix C presents methods for calculating combustion efficiency
improvement and fuel savings resulting from adjustment for low excess oxygen
firing.
4.4 BURNER ADJUSTMENT
The above procedures should result in setting the boiler for low excess
oxygen operation over the entire boiler operating range. Other measures to
attain minimum oxygen requirements include burner control and fuel system
adjustments. Since burner design and combustion controls vary widely, it is
30
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not practical in this general document to provide detailed procedures for the
many systems in use. It is assumed that boiler operating personnel know their
specific burner systems and controls. Additional information should be avail-
able in the boiler operations and maintenance manual or from the boiler manu-
facturer, combustion specialists, and plant engineering staff.
Burner adjustment is essentially a trial-and-error procedure; general
precautions for the above oxygen optimization procedure should be followed.
As adjustments are made the stack, flue gas, and flame conditions should be
monitored closely along with the measurements of oxygen, carbon monoxide,
smoke and temperature to indicate whether the burner adjustments produce the
desired effects. Burner adjustments should be made slowly in small steps, and
adequate time must be allowed for boiler conditions to stabilize before evalu-
ating each change. Special attention should be given to changes in burner
settings or fuel properties that might affect flame stability, flame impinge-
ment and shifts in excess oxygen levels. The boiler manual may give addition-
al information on the range of allowable adjustments.
4.5 MAINTAINING LOW EXCESS OXYGEN
Maintaining low excess oxygen requires conscientious effort by boiler
operator personnel, especially during the first several months as experience
is accumulated for new operating procedures. Special attention should be
given to combustion conditions. For example changes in oil properties, burner
settings, control system settings, damper operation, air heater performance,
etc. may alter fuel/air ratio and excess oxygen levels. Further burner ad-
justments may be necessary if tube fouling or flame problems develop. The
operator should keep track of boiler maintenance requirements and should
thoroughly inspect the burner and furnace surfaces during each boiler outage.
One of the best aids in maintaining low excess oxygen is a periodic spot
check of combustion quality. Stack measurements of oxygen, carbon monoxide,
smoke, and temperature should be taken and compared with the "baseline" read-
ings that were recorded at the same firing rate during the tuning procedure
described in Step 8.
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SECTION 5
MAINTAINING HIGH BOILER EFFICIENCY
The benefits of boiler adjustment can only be realized if steps are taken
to insure that any improvements in boiler efficiency, fuel consumption and
emissions are maintained. Boiler maintenance should focus on every problem
that may degrade boiler performance: e.g., an increase in the temperature,
flow rate, or combustible content of the flue gas; an increase in convective
or radiant heat losses from the boiler shell, ductwork, or piping; or an
increase in blow-down requirements. The discussion of boiler efficiency and
heat losses in Section 3 and the pre-tuning inspection checklists in Section 4
both emphasize efficiency-related maintenance items.
Boiler maintenance has both corrective and preventive aspects. Correc-
tive maintenance is generally performed on an as-required basis whenever
efficiency falls below preset standards. On the other hand preventive main-
tenance consists of periodic cleaning, replacement, and adjustment activities
to reduce the chances of equipment failure or performance deterioration.
Preventive maintenance should reduce the frequency and need for corrective •
maintenance, but it will not totally eliminate corrective maintenance require-
ments. An effective maintenance program uses both preventive and corrective
procedures to maintain efficient boiler'performance.
Basically a maintenance program should routinely monitor the boiler
operation to identify boiler system deterioration and any deviations from
desired performance standards. This requires regular performance measurements
and routine checks for leaks, faulty controls, damage to insulation or refrac-
tory, and other heat losses. These routine observations are compared with
specifications to determine the need for maintenance.
Two basic tools can be used together effectively in an efficiency-related
maintenance program. The first is the routine combustion efficiency spot
check which can provide an early indication of any efficiency-related prob-
lems. The second is the boiler operator's log that documents trends in boiler
condition and performance.
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5.1 COMBUSTION EFFICIENCY SPOT CHECK
Stack measurements of oxygen, carbon monoxide, smoke, and temperature
establish instantaneous combustion conditions that can be compared with "base-
line" standards that reflect optimum boiler adjustments (Section 4.3.3, Step
8). The stack measurements should be conducted under steady boiler operating
conditions. A log or plot of day-to-day data shows trends and helps to iden-
tify the cause and severity of any combust.ion efficiency change. Depending on
the instrumentation available, combustion efficiency spot checks should be
conducted weekly, daily, or even more frequently to reduce the likelihood that
problems will develop that result in fuel waste and pollutant emissions. The
routine and periodic combustion efficiency spot-check can be incorporated into
a systematic tracking procedure from which trends in boiler combustion effi-
ciency and operating parameters can be noted. A tracking procedure to moni-
tor, track, and note trends in boiler performance indicators is presented in
Appendix D.
A change in the excess oxygen level may indicate air or fuel supply prob-
lems or a change in oil properties. Excessive tube fouling, plugged air
passages, air leaks, deteriorated furnace baffling, or changes in atmospheric
pressure can cause shifts in oxygen levels. High excess oxygen levels may
indicate air leaks, low fuel pressure, or a control system malfunction. Low
excess oxygen values suggest improper control system operation or an insuffi-
cient air supply. If the oxygen is normal but the smoke or carbon monoxide
readings are high there may have been changes in fuel characteristics or
burner-related problems. For oil firing the cause may be improper viscosity
or fuel temperature; worn or carbonized burner tips, diffusers, or spinner
plates; poor atomization; or other fuel/air supply problems. For gas firing a
dirty burner is a possible cause; in multiburner installations there may be
unbalanced fuel/air distribution between burners. A 20°F increase in stack
temperature without a corresponding change in excess oxygen, carbon monoxide,
and smoke may be a preliminary indication of furnace baffle deterioration,
fouled tubes, or a soot blower malfunction.
The above examples illustrate only a few of the common causes of deterio-
rating boiler performance and their relationship to spot check measurements.
Other causes may also contribute to boiler efficiency deterioration. It is
important to emphasize that the primary purpose of the combustion spot check
is to provide early warning of an impending efficiency-related problem so that
34
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further action can be taken to correct the problem before fuel waste or exten-
sive maintenance is required. The spot check indicates possible causes, but
it does not diagnose a combustion-related problem precisely.
5.2 BOILER OPERATOR'S LOG AND PERFORMANCE MONITORING
The boiler operator's log is the primary tool for determining the need
for maintenance to restore performance and efficiency. The log documents the
condition and performance of the boiler and provides data to document trends
as a function of time. Performance trends can be used to determine deviations
from performance standards and to establish maintenance procedures. Compari-
son of daily log data with specifications may indicate the need for specific
maintenance. The data provide useful information for various performance and
efficiency checks, for identification of equipment problems, for diagnosis of
problems, and for maintenance scheduling.
Specific items on the log sheet and the frequency at which data are
recorded depend on the size and complexity of the boiler installation. All
measurements should be made during steady load conditions because data taken
during load changes or under fluctuating load conditions are of questionable
value for evaluating efficiency.
The operator's log should contain the following types of information:
0 General data to establish unit output
steam flow rate, pressure, and temperature
feedwater temperature
0 Firing system data
fuel type (in multi-fuel boilers) and characteristics
fuel flow rate
oil or gas supply pressure
pressure at burners
fuel temperature
burner damper settings
windbox-to-furnace air pressure differential
other special system data unique to particular
installation
0 Air flow indication
air preheater inlet oxygen content
stack oxygen content
optional - air flow pattern, forced draft fan damper
position, forced draft fan horsepower requirements
35
-------
0 Flue gas and air temperatures
boiler outlet gas
economizer or air heater outlet gas
air temperature to air heater
0 Combustible indicators
carbon monoxide levels
stack appearance
flame appearance
0 Air and flue gas pressures
forced draft fan discharge
furnace outlet
boiler outlet
economizer differential
air heater air and gas side differential
0 Unusual conditions
steam leaks
abnormal vibration or noise
equipment malfunctions
excessive makeup water
0 Blowdown operation
0 Sootblower operation
0 Safety-related items
water level
feed pump pressure
low water cut out (if applicable)
5.3 INSTRUMENTATION AND CONTROLS
Pressure, draft, temperature, and flow indicators should be calibrated
and serviced routinely. Boiler efficiency will suffer if boiler controls do
not operate properly. Regular inspection checks and maintenance are necessary
to insure that all valves, linkages, control circuits, and safety locks oper-
ate properly.
Steam pressure, temperature, and flow along with air and fuel flow pro-
vide information on the operation of the control system in maintaining desired
boiler operation at various loads. Drum level and feedwater flow indicators
provide necessary information about the boiler water supply. Draft gauges can
indicate fly-ash plugging of the boiler, economizer, or air heater passages.
Gas and air temperature measurements also indicate the need for soot blower
operation. Annunciators (audible alarms) are required to warn the operator of
hazardous operating conditions.
36
-------
Basic instruments for safe boiler control and for documentation of the
operation are listed below. Additional instrumentation is also available.
Indicator Recorder Integrator
Boiler outlet pressure
Superheater outlet steam temper-
ature
Steam flow
Total fuel flow
Total air flow
Individual fuel flow
Oxygen analyzer
Combustibles analyzer
Drum level
Feedwater flow
Draft gauges
Air and gas temperature
Feedwater temperature
Annunciator (audible alarms)
X = Required
0 = Optional
X
X
X'
X
X
X
X
X
X
X
0
0
0
X
0
0
0
5.4 ADDITIONAL CONSIDERATIONS IN A BOILER MAINTENANCE PROGRAM
Important elements of a boiler maintenance program include establishing a
systematic approach and having operation and maintenance manuals, handbooks,
and equipment instructions available to trained personnel who are equipped
with all required maintenance tools, facilities, and parts. The best guide in
establishing a systematic approach to maintenance is past experience. As it
progresses, the program itself will develop experience and provide feedback
that will help to improve the program. Checklists will help to establish
inspection and maintenance routines. Records in the form of reminder cards or
log sheets should also be maintained for individual equipment items in order
to schedule upcoming maintenance and to document completed maintenance.
Entries should indicate maintenance dates and descriptions; who performed the
maintenance; and parts that were replaced, repaired, or cleaned. Parts lists
that indicate part numbers and describe major items are also useful. These
records are especially important in preventive maintenance Where the use of
periodic and routine cleaning, replacement, and adjustment focuses on reducing
the chances of equipment failure or deteriorating performance. In setting up
the maintenance system and procedures, full use should be made of instruction
manuals and handbooks. These publications frequently give detailed informa-
tion on procedures, tools, and facilities that are needed.
37
-------
Correct tools and working facilities are important. Precision parts such
as oil gun tips and burners can be easily damaged when removing deposits or
encrusted carbon. Damage to sealing surfaces and fuel passages during clean-
ing or by dropping onto hard or dirty surfaces can result in leaks, ineffi-
ciency, and malfunctions.
Boiler equipment maintenance should be clearly assigned to reliable,
thoroughly trained personnel. Whenever passible maintenance responsibility
should remain in-house. In some "cases outside maintenance contracts may be
more economical. However, contracts for regular maintenance of major equip-
ment seldom cover routine inspections and repairs that can result in important
efficiency improvements. Thus, even if major items are covered by contract, a
responsible person in-house should conduct general inspection and maintenance
of the installation. Appendix E presents checklists to establish periodic
inspection and maintenance routines on daily, weekly,1 monthly, and annual
bases. These lists can be used to help custom design suitable checklists,
reminder cards, and logsheets.
38
-------
REFERENCES
1. APTI Course 427 Combustion Evaluation - Student Manual, EPA 450/2-80-063.
February 1980.
2. Good Operating Practices for Industrial Boilers, C. M. Schmidt. Novem-
ber 7, 1979.
3. Industrial Boiler Inspection Guide, PEDCo. October 1981.
4. Fuel Efficiency and Safety in the Boiler Room - West Side Institute of
Technology, Cleveland, Ohio. 1979.
5. Applied Combustion Technology - Center for Professional Advancement, East
Brunswick, New Jersey. March 1979.
6 Guidelines for Adjustment of Residential Gas Burners for Low Emissions
and Good Efficiency. D. W. Locklin (Battelle)/R. W. Himmel and
D. W. DeWerth, American Gas Association Laboratories. February 1979.
7. A Guide to Clean and Efficient Operation of Coal-Stoker-Fired Boilers,
American Boiler Manufacturers Association, EPA 600/8-81-016. May 1981.
8. Guidelines for Industrial Boiler Performance Improvement EPA 600/8-77-
003a. January 1977.
9. Guidelines for Burner Adjustments of Commercial Oil-Fired Boilers, EPA
600/2-76-088. March 1976.
10. Guidelines for Residential Oil-Burner Adjustments, EPA 600/2-75-069a.
October 1975.
11. Guidelines for NO Control by Combustion Modification for Coal-fired
Utility Boilers, EPA 600/8-80-027. May 1980.
12. Reference Guideline for Industrial Boiler Manufacturers to Control Pollu-
tion with Combustion Modification-, EPA 600/8-77-003b.
13. Workbook for Operators of Small Boilers and Incinerators, EPA 450/9-76-
001.
39
-------
ways to save °n
40
-------
APPENDIX A
INSTRUMENTATION FOR FLUE GAS MEASUREMENTS
The adjustment procedures outlined in Section 4 require the measurement
of the temperature, the oxygen (or carbon monoxide) and the carbon monoxide
(or combustible) content of the stack gas. Smoke shade measurements are also
useful in detecting incomplete combustion in oil-fired boilers. There is a
wide variation in the sophistication, complexity and capability of the instru-
ments available to make these measurements. Choices vary progressively from
simple, hand-held instruments to panel-mounted recording devices to instru-
ments that provide feedback and automatic control of the combustion process.
Portable instruments are available that use either electronic or chemical
principles to measure the concentrations of one or more flue gas constituents.
Both portable and panel mounted instruments are available.
The selection of an instrumentation system depends largely upon the size
of the boiler facility. For ongoing combustion spot checks and continuous
boiler performance monitoring, particularly at the larger or multi-boiler
facilities,, more sophisticated instrumentation warrants serious consideration
since the cost of instrumentation may be insignificant when compared to the
fuel savings that can be obtained. However, portable instruments are entirely
adequate for performing the adjustment procedures in this manual.
The following pages describe a cross-section of available instrumenta-
tion. The descriptions do not endorse any particular instrument, brand, or
manufacturer, and are presented only to show the variety of available instru-
ments.
CARBON MONOXIDE COMBUSTION TEST KITS AND ANALYZERS
Flue gas (combustion) test kits generally include an oxygen or carbon
dioxide analyzer, a draft gage, a smoke tester, and a thermometer. The kits
are portable, convenient to use and generally cost less than 500 dollars. One
test kit manufacturer claims a carbon monoxide measurement accuracy of ± 0.5
A-l
-------
percent (oxygen is not measured). The kit includes a carbon monoxide indica-
tor, a draft gage, a dial thermometer, a smoke density measurement device, a
stack piercing awl, hole plugs, a combustion efficiency slide rule, instruc-
tions, a carrying case, etc.; the test kit costs approximately 200 dollars.
Combustion efficiency analyzers are available which measure and display
oxygen content, stack temperature, and combustion efficiency. These portable
analyzers operate on batteries, sell for 1'ess than ,1000 dollars, and include a
stack probe with built-in oxygen and temperature sensors and a connecting
cable. A more refined model that also measures smoke shade costs approximate-
ly 1300 dollars.
A portable AC/battery operated device is marketed which measures oxygen,
carbon monoxide, smoke, and stack temperature using a single probe. Measured
values are displayed in digital form; combustion efficiency is also calculated
and displayed. The cost of this combustion efficiency tester/computer varies
from approximately 1500 dollars (for a single liquid or gaseous fuel) to 2500
dollars for a model that can be used on all common liquid or gaseous fuels.
FLUE GAS ANALYZERS (PORTABLE)
The standard Orsat type apparatus is portable and measures oxygen, carbon
monoxide, and carbon monoxide using wet chemistry. An Orsat analysis is
accurate but requires skill, practice and maintenance. The cost of the ap-
paratus is about 500 dollars; it is available from most laboratory equipment
suppliers.
OXYGEN ANALYZERS
Oxygen analyzers are available as portable or panel mounted devices that
use wet chemistry or other detection principles. Those operating on the
chemical absorption principle are simple to use, portable, and accurate and
can be purchased for approximately 100 dollars. Portable units are also
available that use paramagnetic or other measurement principles. The units
display measured values on a digital meter or percent scale. These instru-
ments cost approximately 1000 dollars. Panel mounted AC powered instruments
usually come with a strip chart recorder and cost over 1000 dollars.
A-2
-------
CARBON DIOXIDE ANALYZERS
Portable, easy to use, wet-chemical absorbent-type carbon monoxide test-
ers are available for approximately 150 dollars. Panel-mounted instruments
that employ infrared absorption generally cost over 1000 dollars and may come
with accessories such as a strip chart recorder and a controller.
CARBON MONOXIDE ANALYZERS
Indicator tube type carbon monoxide analyzers use disposable, color-
sensitive chemicals in tubes and a calibrated sampling pump to provide a
length-of-stain carbon monoxide reading. The instruments are very portable
and fairly accurate; they sell for approximately 100 dollars. Panel mounted
instruments of the infrared absorption type generally cost over 1000 dollars
depending on accessories (chart recorder, controller, etc.).
COMBUSTION OXYGEN AND CARBON MONOXIDE (OR COMBUSTIBLE) ANALYZERS
Portable analyzers are available that measure both oxygen and carbon mon-
oxide (or combustible) concentrations and display the values on separate
meters or digital readouts. These battery operated instruments generally use
electrochemical sensors. They contain an integral pump-sampling system and
provide rapid, accurate readings. These portable instruments cost approxi-
mately 2200 dollars. Panel-mounted analyzers are also available for continu-
ous measurement applications.
SMOKE TESTERS
Smoke testers generally use a calibrated hand pump to draw flue gas
through a filter paper for smoke spot determination. The stain is compared
with a set of standard smoke spot numbers (SSN). The kit contains a scale for
evaluating SSN values from 0 to 9 on the Bacharach or ASTM scale. The device
is rugged, portable, and reliable; it requires no calibration and sells for
about 100 dollars.
A-3
-------
AIR PRESSURE GAGES
Manometers and mechanical (aneroid) gages for measuring furnace or stack
draft are simple, accurate, and portable. They are readily available from
most laboratory supply houses for 50 dollars or less.
STACK TEMPERATURES
Stack temperature measurements can be made with dial thermometers, liquid
thermometers, or other temperature sensing devices. Although liquid thermo-
meters generally have greater accuracy, dial thermometers are more rugged.
Dial thermometers with a suitable range for stack temperature measurement
generally cost less than 50 dollars.
A-4
-------
APPENDIX B
ILLUSTRATIVE EXAMPLE - USE OF TEST DATA FROM
THE MINIMUM OXYGEN ADJUSTMENT PROCEDURE
The following hypothetical example illustrates the use of test data from
the procedure described in Section 4.3.4. For illustrative purposes assume
that the data in the following table were recorded during Steps 2 through 5 of
the procedure.
Procedure step
(see Section 4.3.4)
Step 2 (Baseline condition)
Step 3
Step 4 (a)
(b)
(c)
(d)
(e)
(f)
(g)
Oxygen,
Stack readings
Carbon
monoxide,
ppm
7.4
8.6
5.8
4.7
3.8
3.3
2.6
2.1
1.6
1.0
3..0
95
90
98
100
105
130
220
360
520
800
160
Temperature,
°F
475
480
460
456
452
445
441
435
435
432
440
Step 5
Step 8
In this example the baseline oxygen concentration before adjustment was
7.4 percent (Step 2). In following the procedure the combustion air flow was
increased (Step 3) and then reduced in small increments (Step 4) until carbon
monoxide measurements indicated a rapid rise in carbon monoxide concentration
(Step 5). After each adjustment the boiler was allowed to stabilize before
readings were taken. The plot of carbon monoxide and oxygen concentrations is
shown in Figure B-l.
The minimum oxygen level (carbon monoxide limit of 400 ppm) obtained from
Figure B~l is 2.0 percent. The boiler manufacturer recommends an excess
B-l
-------
STEP 5
o 700
o
LU
a
i—<
x
O
600
500 -
CQ
DC
5 400
300
200
100
r-
-I-CO LIMIT - 400 ppm
_L
_L
V BASELINE-STEP 2
_V STEP 3
JL
23456789
OXYGEN (02) IN FLUE GAS, %
10
Figure B-l. Example data: carbon monoxide (ppm) versus oxygen (%).
B-2
-------
oxygen level of 2.5 percent for this model. However, the curve for this
particular boiler installation has a steep characteristic; as oxygen is de-
creased below 3 percent the carbon monoxide concentration rises rapidly.
Suppose also that this boiler is subject to considerable fluctuations in load.
The steep curve characteristic, load swings, and changing atmospheric condi-
tions are factors in the selection of an adequate oxygen safety margin. If a
1.0 percent safety margin is selected, the lowest practical operating level
becomes 3.0 percent oxygen. Considering the above factors this is reasonably
close to the manufacturer's recommendation. The boiler controls are then
adjusted to the 3.0 percent oxygen level, and a final set of readings is taken
(Step 8).
The calculation methods in Appendix C can be used to determine the com-
bustion efficiency improvement and the fuel savings that result from adjust-
ment for low excess oxygen operation. For example, using Figure O2 for a
boiler fired with no. 2 oil and the data for the baseline reading (Step 2 -
7.4 percent oxygen and 475°F) the combustion efficiency before oxygen optimi-
zation was 82.3 percent. The final oxygen setting (Step 8-3.0 percent
oxygen and 440°F) increases the combustion efficiency to 85.7 percent - an
improvement of 3.4 percent. The fuel savings due to the improved efficiency
is 4 percent (3.4 x 100/85.7 = 4 percent).
B-3
-------
-------
APPENDIX C
COMBUSTION EFFICIENCY
The approximate boiler combustion efficiency can be quickly determined
using Figures C-1, C-2 and C-3. To use these figures the temperature and
oxygen (or carbon dioxide) content of the flue gas must be known. Graphs are
presented for boilers fired with natural gas (Figure C-1), Number 2 oil (Fig-
ure C-2), and Number 6 oil (Figure C-3). In those instances where the carbon
dioxide rather than the oxygen content isPknown Figure C-4 can be used to
convert the carbon dioxide reading to an equivalent oxygen value for use in
the graphs. Figure C-4 can also be used to determine the percent excess air
represented by a given oxygen or carbon dioxide value.
To determine combustion efficiency select the graph for the appropriate
fuel and enter the graph along the "oxygen in flue gas" axis. Proceed verti-
cally until the proper flue gas temperature Tine is intersected, pivot and
move horizontally to the combustion efficiency axis.
For example assume the stack measurements for a boiler fired with No. 2
oil are 7.4 percent oxygen and 475°F - the same as the baseline reading in the
illustration in Appendix B. Use Figure C-2 and enter the oxygen content axis
at 7.4 percent proceed vertically to 475°F, pivot, and move horizontally to
read 82.3 percent as the approximate combustion efficiency. In the Appendix B
example the flue gas readings after adjustment for low excess oxygen operation
were 3 percent oxygen and 440°F. The improved efficiency from the No. 2 oil
chart is 85.7 percent.
FUEL SAVINGS
The estimated fuel savings as a result of combustion efficiency improve-
ment can be calculated using the following equation:
(Improved efficiency - original efficiency) x 100%
Estimated fuel savings (Improved efficiency)
C-1
-------
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In the Appendix B case example:
Estimated fuel savings = (85.7 - 82.3) x 100% _
(85.7) ~ 4-°^
The reduction in stack oxygen content from 7.4 percent to 3.0 percent and the
stack temperature reduction from 475°F to 440°F increase combustion efficiency
from 82.3 percent to 85.7 percent and reduce fuel consumption (and cost) by
approximately 4.0 percent.
C-6
-------
APPENDIX D
TRACKING PROCEDURE FOR THE CONTINUING EVALUATION
OF BOILER PERFORMANCE
The full benefits of boiler adjustment can only be realized if steps are
taken to insure that any improvements in boiler efficiency, fuel consumption
and emissions are maintained. Tracking the day-to-day boiler performance and
noting performance trends provides early detection of deteriorating boiler
conditions so that corrective action can be taken before fuel waste or exten-
sive maintenance is required. The tracking procedure presented here can be
easily implemented with a minimum of time, equipment and effort. Operators
will find the procedure useful as a monitoring tool in establishing and main-
taining emission reduction gains, fuel use savings and reliable, efficient
boiler operation. '
The tracking procedure consists of three step-wise segments - the initial
one-time design of data forms and a records handling/filing system, the re-
peated and periodic on-site collection of data, and the final step - compari-
son, evaluation and use of collected data.
PLANT FILES AND DATA FORKS
The use of prepared forms and a simple filing system will ensure that
essential data is collected, properly recorded and securely stored. It is
suggested that at a minimum the records retention and file system should
include:
0 Plant files (folder) that .identify the individual plant (or facil-
ity) by name, location, owner, boiler operator/phone, number of
boilers/boiler ID designations, etc.
D-l
-------
Boiler fact and data record sheets. Within the plant file one each
of a boiler fact sheet and data record sheet should be provided for
each plant boiler. The fact sheet should list such information as
the boiler number (plant ID), make, type, rated capacity, fuel
type(s), boiler operator name/phone, etc. The data record (or
tracking) sheet is used to record key boiler operating and combus-
tion parameters observed or measured during each of the periodic
inspections. Examples of a boiler fact sheet and a data record
sheet are shown in Figures D-l and D-l, respectively.
DATA COLLECTION STEPS
The necessary data for implementing the tracking procedure can be prop-
erly collected and recorded by following the steps listed below:
1. Determine the normal (usual) operating load.
This step is extremely important with respect to tracking procedure
reliability and the inferences to be drawn from comparison with
future data readings. Measurements taken at different load condi-
tions can vary considerably, do not correlate well and the variance
can mask any differences or trends that occur. All future measure-
ments must be made at the same or near-equal load conditions in
, order that meaningful comparisons can be made.
Operate boiler at normal load and await steady load conditions
before making observations and measurements. Steady conditions are
usually indicated by stable stack temperature, steam pressure and
oxygen (or carbon dioxide) flue gas content.
Analyze the composition of stack (exhaust) gases for oxygen (0 ) or
carbon dioxide (CO-) content and presence of combustibles - hydro-
carbon (HC) or caroon monoxide (CO).
Record measurements and observations on the boiler data record
sheet.
2.
3.
4.
5.
o
o
o
o
o
o
Combustion air temperature - degrees Fahrenheit (°F)
Flue stack gas temperature - degrees Fahrenheit (°F)
Flue gas composition from step 3 above - percent (%) of 00
and/or COp and parts per million (ppm) of CO and/or HC.
Boiler operating load - percent (%)
Steam pressure - pounds per square inch gauge (psig)
Steam temperature - degrees Fahrenheit (°F)
Record any appropriate comments or observations that may be helpful
or useful in data evaluation (flame appearance, unusual conditions
or events, new permanent changes, etc.).
D-2
-------
BOILER FACT SHEET
Boiler Operator:
Plant name: .
Phone:
Date:
Industry type:
Address:
No. of boilers at location:
Boiler ID:
Rated capacity:
Fuel(s) data:
0 Type(s):
Make:
Type:
Heating values:
_10 Btu/h Normal operating capacity
Steam data:
_5 ° Rated maximum
, ° Normal (actual) _
0 Pressure
0 Temperature
Steam use is for (comfort heating, process, etc.)
•10° Btu/h
Jb/h
Ib/h
_psig
°F
Boiler operating data:
0 Year round ( ), seasonal ( ) and during months of _
0 Base load unit ( ), swing load unit ( )
0 Alone ( ), in conjunction with other boilers (
0 Burner type: ;
Slowdown is continuous ( ), batch ( )
Water softening system type:
through
)
Water quality testing/control is done: in-house ( ), by contract (. ) -
0 Maintenance is: in-house ( ), by contract ( ) - ; ;—; _
0 Annual maintenance/tune-up, etc. is done: in-house ( ), by contract ( )
during the month of
Figure D-l. Example of Boiler Fact Sheet.
D-3
-------
BOILER DATA RECORD SHEET
Plant:
Boiler ID
Test date
Load
Steam pressure
Steam temperature
Combustion air temp.
Flue gas temp.
C02 - flue gas
02 - flue gas
CO - flue gas
Combustion effeciency
%
psig
°F
°F
°F
%
%
ppm
%
Date
Relevant comments
(flame appearance, furnace conditions, new permanent change;
Figure D-2. Example of Boiler Data Record Sheet.
D-4
-------
6 Determine and record the combustion efficiency using the measured
data The data for flue gas temperature and oxygen content are used
to determine combustion efficiency from the fuel-specific curves of
Figures C-l through C-3 in Appendix C. In the event C02 is measured
rather than 09, Figure C-4 can be used to convert C02 percent to
equivalent 02 percent for use in Figures C-l through C-3.
7. Plot selected key data to show trends. An example format for graph
plots is shown in Figure D-3.
8 Compare previous data with current readings for similar load condi-
tions to detect changes and note trends in combustion parameters and
boiler performance.
Importantly a new set of "baseline measurements" should be recorded after
the annual (or other) outage for maintenance and repair. It is common prac-
tice to clean, refurbish and tune the boilers during the low load summer
months in preparation for the forthcoming heating season. As a result boiler
operating conditions are changed and data from one season are not comparable
with another except in a general way. For purposes of noting trends and
detecting changes in boiler parameters or performance, the comparisons should
only be made between measurements taken during the same heating season and for
similar boiler operating conditions. For this reason a new "baseline" must be
established and recorded upon startup after the annual outage.
Additionally any major changes in boiler operation, fuel, equipment,
water treatment or other such influencing factors can affect measurement
results and the basis for comparison. Consequently substantial changes of a
permanent nature require that a new "baseline" be established for subsequent
data comparisons. Users of this tracking procedure should verify that condi-
tions remain the same and should always be alert to any such changes that may
have occurred since a previous data collection period.
DATA USE
A systematic record of data collected during periodic inspections, combus-
tion efficiency spot checks and boiler log entries can yield an information
base from which trends in boiler combustion efficiency and operating param-
eters can be noted. The tracking procedure uses this data base to monitor
D-5
-------
95
90
o
•z.
UJ
t—t
o
I—I
u.
u.
UJ
CO
o
o
85
80
75
70
--- COMBUSTION EFFICIENCY
OXYGEN
J 1 L.
J L
-I—I I
NOV.
DEC. JAN.
TEST DATES
FEB.
10
9
8
7
6
5
4
3
2
X
o
NOTE: The plots shown are illustrative only. Other measure-
ments such as flue gas temperature, C02» and CO can
also be plotted to show trends with time.
Figure D-3. Example plots of Boiler Tracking Data.
D-6
-------
boiler operations, discover changes with time and detect early-on any deteri-
oration in boiler performance. Early detection and corrective action can
minimize or forestall increases in heat loss, fuel waste, malfunction and
serious repair/maintenance problems that otherwise might occur in the absence
of a systematic scheme for observing, recording and analyzing boiler perform-
ance and operational data.
D-7
-------
-------
APPENDIX E
EXAMPLE INSPECTION/MAINTENANCE CHECKLISTS
Dally Checks and Maintenance Requirements
At a minimum, the following checks should be done on a daily basis. More
frequent checks are advisable.
0 Test low water fuel cut-off.
0 Test water level control.
0 Test and then blow down water column and gauge glass (every shift).
0 Check water level stability, fuel pump pressure, feedwater and
condensate temperature, and steam pressure.
0 Check feedwater system - examine traps, make-up float valves, check
valves, and condensate tank. Blow down all float chambers and check
for leaks.
0 Boiler blowdown - for manual blowdown the frequency and quantity of
blowdown depends on the feedwater condition. For continuous auto-
matic blowdown check system operation and minimize excessive blow-
down.
0 Check fuel supply systems, main fuel valves, and burner controls for
proper operation. Check regulator pressure (gas-firing), fuel
pressure, flow rate, oil temperature, and atomizer steam or air
pressure (oil-firing).
0 Check flue gas temperature at two different settings and compare
with standard established via minimum 02 adjustment procedure.
0 Check 02 analyzer reading (if so equipped) and compare with test
data.
0 Check flame scanner lens, and clean as required.
0 Visually inspect combustion chamber and flame profile.
0 Check all instruments.
E-l
-------
Weekly Checks and Maintenance Requirements
Clean combustion air blower wheels.
Clean air distribution plates.
Clean oil nozzles and atomizing air flow (oil-fired).
Clean and inspect condition of pilot and burner assemblies.
Check safety relief valve for operation and leaks.
Check flame failure and start-up controls.
Check feedwater expansion regulators and check for leaks.
Inspect air cleaners and replace filter media as necessary.
Check exhaust gas composition (02 and C02 , and CO concentrations)
and stack temperature. Compare to 02 optimization test data at same
settings.
0 Check fuel level in oil tanks.
Check all drive belts for tension and wear.
Annual Check and Maintenance Requirements
Inspect the general cleanliness/conditions of the fire (gas) side
and water side of the boiler. Inspect for deposits on furnace
walls evidence of wall heating (bulges or tube swelling), deposits
(scale) on heat transfer surfaces, condition of baffles, refractory
etc. Clean radiant heat transfer surfaces, boiler tube banks
economizers, air heaters, etc. Repair as necessary.
Clean or recondition fuel system - pumps, filters, burners, pilots,
oil preheaters, storage tanks, etc. Inspect and clean burner tips,
diffusers, spinner plates, etc. Check tips for wear, nicks, and
cracks. Inspect and clean burner throat refractory and air regis-
tG
Inspect insulation of boiler surfaces, ducts, steam lines etc and
repair as necessary.
Inspect boiler for casing leaks (smoke tests).
Inspect air and gas ducts, air registers, dampers, and stack for
leaks, deformation, corrosion, etc.
Clean and inspect fans and inlet screens. Examine scroll, rotor
wear plates, seals, and dampers for erosion, cleanliness, alignment
and operation. '
E-2
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0 Dismantle, clean, inspect, calibrate, align, and test the combustion
control system.
0 Clean and inspect the feedwater system. Clean condensate receiver
and aeration systems, clean and recondition feedwater pumps, etc.
Disconnect all linkages, and overhaul and calibrate all parts of the
feedwater regulating system.
0 Clean and inspect the electrical systems. Clean all terminals and
check electronic controls and switches.
0 Clean and inspect all hydraulic/pneumatic valves and check for
proper operation, alignment, and leaks.
0 Remove, clean, and recondition the safety/relief valve system.
0 Replace manhole and handhole gaskets.
0 Change gear case lubricants, and lubricate all bearings as required.
0 Test all safety devices.
0 Tune the boiler for low excess oxygen operation. Record data for
subsequent comparison and adjustment.
Other Periodic Checks and Maintenance Requirements
0 Conduct detailed burner check at least four times per year.
0 Dismantle and clean low water cut-off controls every six months.
0 Every three to four months have automated combustion controls
(meters, activators, and controllers) checked by competent service
organizations.
E-3
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1. REPORT NO.
4. TITLE AND SUBTITLE
Combustion Efficiency Optimization Manual
for Operators of Oil- and Gas-Fired Boilers
TECHNICAL REPORT DATA .
(Please read Instructions on the reverse before completing)
2.
7. AUTHOR(S)
Jack A. Wunderle
Thomas C. Ponder
. RECIPIENT'S ACCESSION NO.
. REPORT DATE
September 1983
. PERFORMING ORGANIZATION CODE
3. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
PEDCo Environmental, Inc.
11499 Chester Road
Cincinnati, Ohio 45246
11 CONTRACT/GRANT NO.
68-01-6310
Task Order No. 54
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Stationary Source Compliance Division
401 M Street, S.W.
Washington, D.X. 20460
13. TYPE OF REPORT AND PI
Final Report
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This manual provides general guidance to operators of oil- and gas-fired
boilers to increase boiler efficiency, improve fuel consumption, and to
reduce pollutant emissions. Boiler operating principles and suggestions to
improve boiler performance are discussed. Combustion is explained in simple
terms Various heat losses are described, and suggestions are given on means
to minimize or eliminate heat losses. The manual describes boiler adjustments
for peak operating efficiency, optimum fuel consumption, and reduced pollutant
emissions. Efficiency, fuel consumption, and emissions are all sensitive to
many of the same boiler operating parameters. This manual describes feasible
operating techniques and combustion adjustments to achieve clean, safe, and
efficient boiler operation.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Boiler Operation
Combustion Efficiency
I.IDENTIFIERS/OPEN ENDED TERMS
COSATl Field/Group
|18. DISTRIBUTION STATEMENT
Unlimited
Unclassified
71
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-URev. 4-77) PREVIOUS EDITION is OBSOLETE
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