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

-------
                                   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.

-------
                                   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

   v

   1

   1
   1
   2
   3
   4
   7
  12

  15
  15

  18
  22
  30
  31

  33

  34
  35
  36
  37

  39

-------
                             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

-------
                                    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

-------

-------
                                    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.

-------
     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.

-------
                                    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.

-------
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.

-------
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

-------
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.

-------
                                    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.

-------
     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

-------
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

-------
   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

-------
    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).
                                  11

-------
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
                                       12

-------
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.
                                       13

-------
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 10F 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.
                                       14

-------
                                   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).
                                       15

-------
     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.
                                       16

-------
     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

-------
     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.
                                       18

-------
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

-------
     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

-------
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.
                                       21

-------
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

-------
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:
                                       23

-------
i- >
O E
   o
^"^^^
z: ->
to rc$
co $-
 S- O>
 O) O
J3 =
 E O
 3 O

   (/>
4J res
 o o>

 I/) OJ
   3
 SO Q-
CO (_> O.
              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

-------
           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.

                                       25

-------
     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

-------
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

-------
          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

-------
     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.
                                        29

-------
      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

-------
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.
                                       31

-------

-------
                                   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.

                                        33

-------
  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 20F  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

-------
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 475F) the combustion efficiency before oxygen optimi-
zation was 82.3 percent.  The final oxygen setting (Step 8-3.0 percent
oxygen and 440F) 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 475F - 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 475F, 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 440F.  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

-------
                                                                                                                          in  en
                                                                                                                          re  e
                                                                                                                          OVi-
                                                                                                                         U 4-
                                                                                                                         ro
                                                                                                                             ro
                                                                                                                         O i
                                                                                                                             ro
                                                                                                                         p  ro
                                                                                                                         u  c
                                                                                                                         ro
                                                                                                                            P
                                                                                                                         in c:
                                                                                                                         ro O)
                                                                                                                        i- C
                                                                                                                         O d)
                                                                                                                        r- O)
                                                                                                                         
-------
                                                           in   .
                                                           m O5
                                                           TO c
                                                           U T-
                                                           (C > o
                                                           u  o
                                                           c.
                                                           o>  c
                                                           !-  CU
                                                           (J  CD
                                                           <*-  O
                                                            01
                                                            C  (0
                                                            O  D)
                                                            in  3
                                                            3  r-
                                                               -o
                                                               cu
                                                           CM  J-
                                                            I   3
                                                           O  -P
                                                               ro
                                                            cu  &-
                                                            s-  cu
                                                            3  Q.
                                                            en e
                                                           i-  Ol
C-3

-------
       o    o    o
       O   O   O
       in   o   m
       CM   ro   m
o
o
o
o
O
LO
O
O
O
o
o
LT>
in
o
o
o
10
O
O
LO
O
O
o
OO
OO
LD  o
i^~  co
              o
OOo    O
OOO   O
u->  o   un   o
co  cr>
cr>  oo   oo  oo  co  oo
                                                                                                 in
                                                                                                 ro O)
                                                                                                 01 c

                                                                                                ^ tl
                                                                                                 (J !-
                                                                                                 ro 4-
                                                                                                p
                                                                                                 in i 
                                                                                                   
                                                                                                4- O
                                                                                                c
                                                                                                o  .
                                                                                                r- O
                                                                                                <-> z
                                                                                                (J
                                                                                                c s-
                                                                                                3 O
                                                                                                m -i->
                                                                                                   c
                                                                                                U5 O)
                                                                                                ro -(->
                                                                                                   c
                                                                                                >1 O
                                                                                                U   O)
                                                                                                CO  3
                                                                                                3 r
                                                                                                J3 <-

                                                                                                o -a
                                                                                                c_>  c
                                                                                                   ro
                                                                          CO
                                                                           I
                                                                          O

                                                                           01
                                                                                                   a>
                                                                                                   S-
                                                                                                   ro
                                                                                                   S-
                                                                                                ^  
-------
oo
_l
14
o
oS


CM
O

VO
o

CM
                                                                        in
                                                                        m
                                                                     v>  en
                                                                     (0
                                                                     O>i 
                                                                        TO
                                                                     Q)  J-
                                                                     3  3
                                                                    <  4->
                                                                    
                                                                                          u
                                                                                          X  S-
                                                                                          
                                                                                              en
                                                                                          01  >,
                                                                                          >  X
                                                                                          r-  O

                                                                                          (C <4-
                                                                                          S-  O
                                                                                          (C
                                                                                          D. V)
                                                                                          E  C
                                                                                          O  O

                                                                                              +J
                                                                                              (D
                                                                                            .  S-

                                                                                           I  C
                                                                                          cj  oi
                  QNV

-------
      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 475F to 440F 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
tt
o
II
u.
u.
UJ
CO
o
o
85
   80
   75
   70
                                   --- COMBUSTION  EFFICIENCY
                                        OXYGEN
        J	1	L.
                                    J	L
                                             -II   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

-------
    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

-------

-------
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

-------

-------