May 1981
EPA-600/8-81-016
A GUIDE TO CLEAN AND EFFICIENT OPERATION
OF COAL-STOKER-FIRED BOILERS
Guidelines intended for use:
- by personnel responsible for boiler operation
to perform an efficiency and emissions tune-up
- by plant engineers to initiate maintenance and
efficiency monitoring practices
- as a supplement to manufacturer's service
instructions
American Boiler
Manufacturers Association
1500 Wilson Boulevard
Arlington, VA 22209
U.S. Department of Energy
Fossil Energy
Office of Coal Utilization
Washington, DC 20545
U.S. Environmental
Protection Agency
Office of Research
and Development
Industrial Environmental
Research Laboratory
Research Triangle Park, NC 27711
-------
EPA REVIEW NOTICE
This report has been reviewed by the participating Federal Agencies,
and approved for publication. Approval does not signify that the contents
necessarily reflect the views and policies of the Government, nor does mention
of trade names or commercial products constitute endorsement or recommendation
for use.
This document is available to the public through the National Technical
Information Service, Springfield, Virginia 22161.
-------
FOREWORD
This guide has been prepared by the American Boiler Manufacturers
Association (ABMA) under contract to the United States Environmental Protection
Agency and the United States Department of Energy to provide operators and
owners of coal stoker fired boilers with information as to techniques and
procedures which may be used to improve operating efficiency while reducing
boiler emissions.
The guide was prepared under the supervision of the ABMA Stoker
Technical Committee and is based on a program of field tests conducted as a
part of research into factors affecting performance of stoker fired boilers.
The principal author is Peter L. Langsjoen of KVB, Incorporated. Contributions
of ABMA members have also been incorporated.
The contents of this guide are offered as guidance only. The American
Boiler Manufacturers Association, KVB, Inc., and the United States Government
and their employees do not assume responsibility or liability for consequences
arising from the implementation or failure to implement the guidance contained
herein. The contents of this guide should not be construed as an endorsement
by the EPA, DOE or ABMA of any product or manufacturer.
This guide is intended as a supplement to the manuals furnished by the
equipment manufacturers who should be consulted regarding operational or equip-
ment problems.
William H. Axtman
Executive Director
American Boiler Manufacturers Association
KVB4-15900-560
-------
ABSTRACT
This report was prepared as a set of guidelines for those in charge
of operating coal stoker fired boilers. It explains and illustrates the dif-
ferent types of coal stokers in operation today. It explains the combustion
process in simple terms, specifically as it relates to stoker coal combustion.
It explains the various heat losses in stoker boilers and how they may be
minimized. Most importantly, it discusses ways in which coal stoker fired
boilers may be operated at peak efficiency and with minimum pollutant emissions.
Included are step-by-step procedures for optimizing excess air levels.
The guidelines are based on the findings of an extensive coal stoker
test program conducted for the American Boiler Manufacturers Association (ABMA)
by KVB, Inc., between August, 1977, and November, 1979. This report was sub-
mitted in partial fulfillment of Contract No. IAG-D7-E681 (EPA) and EF-77-C-01-
2609 (DOE).
KVB4-15900-560
11
-------
CONTENTS
Foreword ........... .. i
Abstract ii
Figures .... ........... iv
Acknowledgment .............. vi
1. Introduction ..... .... 1
2. Stokers in Use Today . 3
Underfeed Stokers ..... 3
Overfeed Stokers 7
Spreader Stokers 10
3. The Combustion Process 13
The Chemical Reaction 13
The Composition of Coal and Air 14
Steps in the Combustion of Coal in Stoker-Boilers 15
Requirements for Complete Combustion 18
Products of Combustion 20
Summary 22
4. Boiler Efficiency 23
Conservation of Energy 23
Boiler Efficiency 23
Stack Gas Heat Loss 25
Combustible Heat Loss 26
Radiation Heat Loss 27
Slowdown Heat Losses .....' 28
Summary 28
5. Guidelines for Clean and Efficient Boiler Operation 29
Boiler Maintenance 29
The Operator's Log 30
Optimizing the Excess Air 32
Overfire Air 46
Cinder Reinjection 48
Firing Rate 48
Coal Properties 49
Summary 56
References 57
Bibliography 58
Appendices
A. Conversion Factors - English and Metric Units to SI Units .... 60
B. Conversion Factors - SI Units to English and Metric Units .... 61
C. SI Prefixes 62
D. Emission Units Conversion Factors for Typical Coal Fuel 63
E. ASME Test Form for Abbreviated Efficiency Test-Summary Sheet ... 64
F. ASME Test Form for Abbreviated Efficiency Test-Calculation Sheet . 65
G. ABMA Standard Radiation Loss Chart 66
111
-------
FIGURES
Number Page
1. Single Retort Underfeed Stoker with Side Dumping Grates . . . . 4
2. Cross-Sectional View of Single Retort Underfeed Stoker in
Operation . . „ . „ 5
3. Multiple Retort Underfeed Stoker Showing Details of Components 5
4. Side View of Multiple Retort Underfeed Stoker 6
5. Side View of Chain Grate Overfeed Stoker ...... 7
6. Side View of a Traveling Grate Overfeed Stoker 8
7. Side View of a Water-Cooled Vibrating Grate Stoker 9
8. Side View of a Mechanical Coal Feeder Showing Components .... 10
9. Dumping Grate Spreader Stoker 11
10. Side View of a Spreader Stoker with Traveling Grate 12
11. Analogy of a Chemical Reaction 14
12. Composition of Dry Air and a Typical Coal 14
13. Major Heat Losses in Stoker Boilers 24
14. High Pressure Power Boiler Log Sheet for Twice Daily Readings . 31
15. High Pressure Boiler Log Sheet for 24-Hourly Readings 32
16. Carbon Monoxide and Smoke vs Excess Air. This Figure Illustrates
the use of a Safety Margin to Set an Optimum Excess Air Level. . 33
17. Combustion Chart for Determining Excess Air from either Flue Gas
Oxygen or Carbon Monoxide (Dry Basis) while Firing a Bituminous
Coal 34
18. Combustion Chart for Determining Total Air from an Orsat Flue
Gas Analysis 35
19. This is a Plot of the CO - ©2 Data Given in the Example .... 39
20. Stack Gas Heat Loss as a Function of Stack Gas Temperature and
Stack Gas Oxygen for a Typical Bituminous Coal 41
21. Excess Air Trends for Five Overfeed Stokers 44
22. Excess Air Trends for Six Spreader Stokers Obtained over a Wide
Range of Firing Rates 45
23. The Relationship Between Nitric Oxide and Excess Air on an Over-
feed Stoker 46
24. The Effect of Overfire Air Pressure on the Uncontrolled Particu-
late Loading on an Overfeed Stoker 47
25. Uncontrolled Particulate Loading as a Function of Boiler Loading
on a Spreader Stoker 49
IV
-------
FIGURES
Continued
Number Page
26. The Effect on Uncontrolled Particulate Loading of Washing a Coal
to Reduce its Ash Content. . . 50
27. ABMA Recommended Limits of Coal Sizing for Underfeed Stokers ... 52
28. ABMA Recommended Limits of Coal Sizing for Overfeed Stokers. ... 53
29. ABMA Recommended Limits of Coal Sizing for Spreader Stokers ... 54
-------
ACKNOWLEDGEMENTS
The authors wish to express their appreciation for the assistance and
direction given the program by project monitors W. T. Harvey and W. Siskind of
the United States Department of Energy (DOE) and R. E. Hall of the United States
Environmental Protection Agency (EPA) . Thanks are due to their agencies, DOE
and EPA, for co-funding the program.
We would also like to thank the American Boiler Manufacturers Association,
ABMA Executive Director, W. H. Axtman, ABMA Assistant Executive Director, R. N.
Mosher, ABMA1s Project Manager, B. C. Severs, and the members of the ABMA Stoker
Technical Committee Chaired by W. B. McBurney of The McBurney Corporation for
providing support through their time and travel to manage and review the program.
The participating committee members listed alphabetically are as follows:
R. D. Bessette Island Creek Coal Sales Company
D. Clayton Combustion Engineering, Inc.
T. Davis Combustion Engineering, Inc.
N. H. Johnson Detroit Stoker Company
W. E. Krauss Cleaver Brooks Division
K. Luuri Riley Stoker Corporation
K. J. McNamara Riley Stoker Corporation
D. McCoy E. Keeler Company
W. R. Murray Foster Wheeler Limited
E. A. Nelson Zurn Industries, Inc.
E. G. Poitras The McBurney Corporation
P. E. Ralston Babcock & Wilcox Company
D. C. Reschley Detroit Stoker Company
R. A. Santos Zurn Industries, Inc.
J. F. Wood Babcock & Wilcox Company
This document has been reviewed and approved for publication by the
Stoker Technical Committee of the American Boiler Manufacturers Association (ABMA),
by the U. S. Environmental Protection Agency (EPA), and by the U. S. Department
of Energy (DOE). This document was written by KVB, Inc. The principal author
was P. L. Langsjoen, P.E..
VI
-------
SECTION 1
INTRODUCTION
This manual has been written for boiler operators and is intended to
be a concise, easily understood and interesting guide to the clean and efficient
operation of bituminous and sub-bituminous stoker coal-fired boilers. It should
be made very clear, however, that this manual neither replaces nor supercedes
the manufacturer's operating manual for your boiler. The manual will explain
general principles of boiler operation and will suggest ways of reducing boiler
emissions and increasing boiler efficiency. But the manual will not show you
how, exactly, to implement these suggestions. For that you must consult your
boiler manufacturer's operating instructions. You, then, must decide how to
implement a sensible emission control and/or boiler efficiency program.
The first section of the manual describes the types of stoker boilers
in use today. Since stokers of different design have different operating
characteristics, this part of the manual will explain the peculiarities of each
type of design so you can better understand how to deal with problems specific
to the type (s) of stoker you are operating. The next section of the manual
explains, in a concise and simple way, the combustion process. Understanding
this process will allow you to control it better. Since both increased boiler
efficiency and reduced boiler emissions can be achieved most inexpensively through
combustion control, a basic understanding of the combustion process is essential
to achieving improved boiler operation. The last two sections of the manual ex-
plain how you can control the combustion process in your coal stoker-fired boiler
in such a way as to achieve increased boiler efficiency and reduced emissions.
While it is frequently possible to achieve increased efficiency and reduced
emissions simultaneously/ there is sometimes a tradeoff between the two. The
nature of this tradeoff is explained in the last two sections of the manual.
This document draws upon the extensive experience gained during the
industrial coal stoker-fired boiler test program conducted by KVB, Inc., for
the American Boiler Manufacturers Association (ABMA). (Ref #1-12)
KVB4-15900-560
-------
SECTION 2
STOKERS IN USE TODAY
In the early days, a "stoker" was someone employed to tend a furnace.
To stoke a fire meant to do whatever was necessary to keep it burning properly,
including poking, stirring, and supplying it with fuel. Eventually these
"stokers" were replaced with mechanical devices which automatically fed fuel
to the furnaces, and in some cases automatically disposed of the ash. These
were called mechanical stokers, and first appeared in the 1800's.
Today, there are a variety of mechanical stokers in use. They differ
in the way in which solid fuel is fed onto the grate, and they differ in the
way in which ash is removed from the grate. Each method of firing has its own
unique operating characteristics, and each has its own best applications. This
section will discuss the types of mechanical stokers which are commonly used
today for firing coal.
Today's stokers can be sorted into three categories based on the way
in which fuel is fed onto the grate. These categories are: (1) underfeed
stokers, (2) overfeed stokers, and (3) spreader stokers. Within each category,
the stokers differ according to the way in which the grate handles the ash.
Each stoker category will be discussed, and the most common stoker types will
be illustrated.
UNDERFEED STOKERS
In an underfeed stoker, the fuel is introduced through long troughs,
called "retorts", at a level below the location of air admission to the fuel
bed. Thus, the green coal (or raw coal) is at the bottom, the ash moves away
from the retort, and combustion takes place in between, constantly receiving a
fresh supply of green coal from below and displacing the ash.
Underfeed stokers were developed in the 1800's, and were very popular
before World War II. After World War II, they were gradually replaced by larger
spreader stokers and overfeed stokers. However, they have many useful appli-
cations and are still being sold today.
KVB4-15900-560
-------
The smallest of the underfeed stokers have a single or double retort
into which the coal is fed. The coal feed is by either a screw or a mechanical
ram which forces the coal the length of the retort and upward. The ash on this
type of stoker is normally discharged with side dumping grates. These stokers
will fire boilers in the size range of 3,000 to 30,000 pounds of steam per hour.
Figure 1 shows what a typical single retort stoker looks like, and Figure 2
shows a cross section of this stoker in a furnace and how it would look in operation
Note how the ash moves to the sides where it can be periodically dumped into ash
pits and removed. Note also that the "tuyeres", through which air is admitted, are
above the retort.
Figure 1. Single Retort Underfeed Stoker with Side Dumping Grates.
(Reprinted with Permission of Detroit Stoker Company)
Some underfeed stokers have grate sections which have an undulating
(wave-like) action to break up clinkers from high-coking coals so that manual
poking is reduced. Most modern underfeed stokers are also equipped with overfire
air jets to provide turbulence to mix the volatiles with the air for more complete
combustion.
KVB4-15900-560
-------
Figure 2. Cross-Sectional View of Single Retort Underfeed Stoker
in Operation. (Reprinted with Permission of Detroit
Stoker Company)
The larger underfeed stokers are of the multiple retort type having as
many as twelve retorts inclined at an angle of 25° to 30° to aid the movement of
coal and ash. Illustrations of this type of stoker are given in Figures 3 and
4. In this type of stoker, the ash is discharged at the rear either intermittently
with a dumping grate or continuously as it is displaced by the burning coal.
Figure 3. Multiple Retort Underfeed Stoker Showing Details of Com-
ponents. (Ref #13) (Reprinted with Permission of Detroit
Stoker Company)
KVB4-15900-560
-------
Tuyeres
Coal Hopper
Coal
Rams
Ash Discharge Plate
Fuel Distributors
Figure 4. Side View of Multiple Retort Underfeed Stoker. (Ref #14)
(Reprinted with Permission of Detroit Stoker Company)
The multiple retort stoker employs large mechanical rams and pusher
blocks to feed and distribute the coal. It also employs overfire air when
necessary. These units are used in boilers which range in size from 20,000 to
500,000 pounds of steam per hour.
It can be seen from Figures 2 and 4 that underfeed stokers operate with
very thick fuel beds. This results in a high thermal inertia, or a slow response
time to changes in steam loading. They also have trouble burning certain grades
of coal, such as high-coking coals, which form a coke that expands and arches
off the grate, and free burning sub-bituminous coals whose loose ash leave
sections of the grate bare causing overheating and grate damage. Low ash bituminous
coals when burned may not generate sufficient ash to protect the grate surface.
On the positive side, underfeed stokers have a clean smokeless combustion
when fired with the proper coals, and they have low flyash carryover. The smoke-
less combustion results from feeding the coal from underneath the combustion zone.
As the coal is heated, the volatiles are driven off and pass upward through the
incandescent, burning coals where most are consumed before they pass completely
through the fuel bed.
KVB4-15900-560
-------
OVERFEED STOKERS
In an overfeed stoker, the coal is fed onto the grate above the point
of air admission. The two basic types of overfeed stokers are the chain, or
traveling grate stoker, and the water-cooled vibrating grate stoker. Technically,
a spreader stoker is also a type of overfeed stoker. However, because it is
commonly considered in a class by itself due to its unique features, it will
be classified separately in this text.
A typical chain grate overfeed stoker is illustrated in Figure 5. It
consists of a continuously moving grate. Coal is deposited on one end of the
grate by gravity feed from a coal hopper. The coal depth is adjusted by a
guillotine-like movable coal gate to a thickness of about 4 to 12 inches. The
coal is burned as it passes slowly through the furnace at grate speeds of less
than 30 feet per hour. The ash is continuously discharged off the rear of the
grate into an ash pit.
Coal Hopper
Drive ^
Linkage
Drive
Sprocket
Sittings
Hopper
Sittings Dump
Mechanism
Air Seals Air Compartments
Figure 5. Side View of Chain Grate Overfeed Stoker. (Ref #14)
(Reprinted with Permission of LacLede Stoker Company
KVB4-15900-560
-------
There are different types of grate construction in use. These are
classified either as chain or traveling grates, although the chain grate also
travels. In the chain grate, the grate itself is a wide chain composed of close-
fitting links. The air passes upward through the spaces between the links. In
the traveling grate, grate sections called "bars" or "links" are attached to a
separate chain. A typical traveling grate stoker is illustrated in Figure 6.
Traveling
Grate
Surface
Figure 6. Side View of a Traveling Grate Overfeed Stoker. (Reprinted
with Permission of Riley Stoker Corporation)
Undergrate air is controlled through individual air zones or compartments
underneath the grate. The amount of air entering each zone is manually controlled
by the operator. Many of the overfeed stoker-fired boilers have a rear arch which
directs any remaining volatile gases and cinders from the burnout zone back towards
the flame zone where they may be burned. One or two rows of high-pressure overfire
air jets are used on the front waterwall to mix the volatiles with the air for more
complete combustion. Chain and traveling grate stokers have been built for boilers
as large as 200,000 pounds of steam per hour.
KVB4-15900-560
-------
The water-cooled vibrating grate stoker uses vibration and gravity to
move the coal. This type of stoker originated in Europe and was introduced to
the United States in the mid 50's. It is illustrated in Figure 7.
It consists of a water-cooled grate supported by flexing plates and in-
clined at an angle of about 14°. Coal is gravity fed at the top of the grate
and passes under a guillotine-type gate which controls the bed thickness. The
grate is vibrated for about 5 seconds every two minutes. The interval and
duration of the vibrations is tied to the automatic controls, and determines the
rate at which the coal is moved through the active burning zone. Ash is dis-
charged at the rear of the stoker.
OverfireAir Coal
Hopper
Grate
Tuyere
Blocks
Coal
Gate
Air Control Dampers Flexing Plates Vibration Generator
Figure 7. Side View of a Water-Cooled Vibrating Grate Stoker.
(Ref #14) (Reprinted with Permission of Detroit Stoker
Company)
As with the chain and traveling grate stokers, the vibrating grate stoker
has individually controlled air zones. The boiler often has a rear arch to direct
any remaining volatile gases from the burnout zone back into the active combustion
zone. It also uses high-pressure overfire air jets on the front wall to promote
mixing of the volatile gases and the air for more complete combustion.
In general, overfeed stokers are characterized by low flyash carryover.
They burn most coals, although high-coking coals may be a problem. The overfeed
stoker's response time to rapid changes in load is slower than that of the spreader
stoker, and such stokers require a larger grate size for a given heat input than
a spreader stoker.
KVB4-15900-560
-------
SPREADER STOKERS
In a spreader stoker, coal is spread evenly over the entire grate surface
by mechanical feeders located at the stoker front above the grate. Because the
coal is thrown onto the grate, there is some suspension burning of the coal fines.
This suspension burning coupled with a very thin fuel bed allows the spreader
stoker to respond to rapid load changes.
There are many types of mechanical feeders in operation. They all utilize
rotor speed and coal trajectory to adjust coal distribution on the grate. One type
of mechanical feeder is illustrated in Figure 8. In this typical arrangement, coal
is pushed over the edge of a "spill plate" onto a rotating "overthrow rotor". The
rotor has paddles on it and is spinning at several hundred revolutions per minute.
As the coal moves over the "spill plate", it is struck by the paddles and is
thrown into the furnace. The paddles are designed to distribute the coal over a
wide area. The rotor speed, spill plate position, and sometimes the paddle
orientation can be adjusted to provide an even distribution of coal on the grate.
The number of feeders used depends on the width of the stoker grate.
Coal Hopper \.
Reciprocating
Feed Plate
Ash Door
Figure 8. Side View of a Mechanical Coal Feeder Showing Components.
(Ref #14)(Reprinted with Permission of Detroit Stoker
Company)
KVB4-15900-560
10
-------
Figure 9. Dumping Grate Spreader Stoker. (Reprinted with
Permission of Zurn Industries, Inc.)
Spreader stokers include a wide variety of grate types. One type is
the dumping grate spreader stoker. The grate bars on a dumping grate stoker
rotate open like Venetian blinds so that the ash will fall into an ash pit
underneath the grate. As illustrated in Figure 9, this type of stoker is built
with two or more independent dumping sections. When the ash builds up on one
section, the coal feed is stopped to that section and the fire allowed to burn
down. At the same time, the coal feed is increased to the other sections to
prevent a drop in steam pressure. When the fire has burned down on the one
section, the undergrate air is shut off to that section only, the ashes dumped,
and the air and coal feed resumed. When the fire has been reestablished on the
dumped section, the process is repeated on the other sections. Dumping grate
stokers have been built for boilers in the size range of 15,000 to 75,000 pounds
of steam per hour.
The larger coal-fired spreader stokers use continuous ash discharge
grates. The most popular version of this type of grate is the traveling grate.
Reciprocating grates and vibrating grates are also sold but are less popular.
KVB4-15900-560
11
-------
A typical arrangement of a spreader stoker with traveling grate is
illustrated in Figure 10. Note that the ash is discharged at the front of the
stoker rather than at the rear. The spreader stoker is usually equipped with
overfire air jets front and rear to provide turbulence for mixing the volatile
gases with the air, and to hold the flames off the water walls and out of the
feeder throat. Spreader stokers are usually not equipped with separately con-
trolled undergrate air zones because these have been found to be generally unneces-
sary. Traveling grate spreader stokers have been built for boilers as large as
400,000 pounds of steam per hour.
Coal Hopper
Feeder
Stoker
Chain
Figure 10. Side View of a Spreader Stoker with Traveling Grate. (Ref #14)
(Reprinted with Permission of Detroit Stoker Company)
The spreader stoker is characterized by a thin bed and partial suspension
burning. As a result, it responds rapidly to changes in load. It is capable of
firing a wide range of coal grades and types. The spreader stoker has high
availability, simplicity of operation, and high operating efficiency, but it has
high flyash carryover and a high flyash combustible heat loss. Cinder reinjection
is used on spreader stokers to recover some of the carbon in the collected flyash.
KVB4-15900-560
12
-------
SECTION 3
THE COMBUSTION PROCESS
Combustion is a chemical reaction in which oxygen combines rapidly
with elements in the fuel to form new compounds and heat. This heat is used
to produce steam or hot water in boilers. The new compounds, or products of
combustion, are primarily carbon dioxide and water vapor which exit the boiler
through the stack.
It is the boiler operator's job to maintain the safety and efficiency
of the combustion process, and to minimize the undesirable products of combustion
such as carbon monoxide, nitric oxides and particulates to name just a few. To
do this, the operator must understand the combustion process. He need not have
the technical background of a combustion engineer, but he does need to understand
how his actions affect the combustion process. That is what this section is all
about.
THE CHEMICAL REACTION
First, let's look at combustion on a molecular level to see what is
happening.
Consider the combustion of carbon. Carbon (C) combines with oxygen (02)
to form carbon dioxide (CO2>. This reaction releases energy in the form of
heat. A chemist writes the reaction equation like this:
C + 02 ->• C02 + heat
That's fine, you might say, but there is oxygen in the air and carbon
in this lump of coal so why don't they react and ignite in my hand? The reason
they don't react at room temperature is that there is a barrier between the
carbon atoms and the oxygen molecules which keeps them apart. The carbon and
oxygen must collide with enough energy to overcome this barrier before they
will react. The energy required to overcome the barrier is heat energy.
Exactly what is heat? Heat can be thought of as motion on a molecular
level. When something is heated up, its molecules move around or vibrate more
vigorously. For example, when a hot object touches something cooler, it transfers
some of its energy of motion to the cooler object. The combined energy of the
KVB4-15900-560
13
-------
two objects remains unchanged. Therefore, the hot object cools and the cool object
heats up until their molecular motion are the same. Then they are at the same
temperature.
In the chemical reaction of carbon and oxygen, it takes a certain amount
of heat energy to overcome the barrier, but once the barrier is overcome, a larger
amount of energy is released. The result is a net gain in energy. A good analogy
is pushing a cart over the crest of a hill. The cart won't roll down the other
side until it is pushed over the crest. So you put a little energy into the cart
to get it over the crest but gain much more energy as the cart rolls down the other
side of the hill. This analogy is illustrated in Figure 11.
Small Energy Input
Large Energy Output
Figure 11. Analogy of a Chemical Reaction
THE COMPOSITION OF COAL AND AIR
Coal has more than just carbon in it, and air has more than just oxygen.
Therefore, the combustion of coal involves a number of chemical reactions. First,
let's look at what coal and air are composed of. This is shown in Figure 12.
Composition of
Dry Air by Volume
Composition of
a Typical Coal by Weight
Ash, 10%
Oxygen, 8%
Hydrogen, 5%
Nitrogen, 2%
Sulfur, 1%
Carbon, 74%
Figure 12. Composition of Dry Air and a Typical Coal
14
KVB4-15900-560
-------
The important reactions for producing heat from coal involve carbon (C),
hydrogen (H2)/ and oxygen (O). There are other reactions which occur, but these
don't add much to the heating value of the coal. These minor reactions are
responsible for some of the air pollutants and are explained later. The primary
heat producing reactions are:
02 + C -*• C02 + 14,100 Btu per pound of carbon
02 + 2H2 •+ 2H2O + 61,100 Btu per pound of hydrogen
This means that the flue gas is mostly carbon dioxide (CO2), water vapor
(H2O), and nitrogen (N2). Where did the nitrogen come from? Most of the nitrogen
in the air did not react with anything, it just passed through the boiler. A
typical flue gas from a coal-fired stoker might contain:
Typical Flue Gas Analysis
12% carbon dioxide (CO2)
6% water vapor (H20)
74% nitrogen (N2)
8% oxygen (G>2)
STEPS IN THE COMBUSTION OF COAL IN STOKER-BOILERS
In actual practice, the combustion of coal is more complex than meets
the eye. The following events take place when coal is burned in a stoker.
Moisture is Driven Off
Moisture is driven off from the coal when it first enters the hot furnace.
The more moisture there is, the longer it takes for the coal to heat to its
ignition temperature and, thus, the harder it is to ignite the coal.
The process of removing the moisture from the coal is similar to boiling
water on the stove. The water and its container remain at 212°F until all the
water has been boiled off because the vaporization of the water absorbs heat as
fast as it is added. Only when all the water has boiled off will the pot heat
up further. Likewise, the heating of the coal is slowed down by the vaporization
of its moisture.
KVB4-15900-560
15
-------
While on the subject of moisture, it is worthwhile noting that there
are two forms of coal moisture. There is surface moisture produced by conditions
at the mine or by rain, and there is inherent moisture which is a part of the
coal and which does not produce wetness. Inherent moisture is usually found in
the following concentrations: (Ref #15)
Bituminous Coals 2 - 17% moisture
Sub-bituminous Coals 15 - 30% moisture
Volatiles are Driven Off
As the coal continues to heat up, it partially decomposes giving off
gases. These gases are called its volatile matter. Typically, 20 - 40% of
the coal's weight becomes volatile matter. Some of this volatile material is
noncombustible, but most of it will burn. The combustible gases include hydrogen,
carbon monoxide and hydrocarbons such as methane.
The volatiles help to ignite the coal in the same way that kindling
helps to ignite a log fire. The volatiles have a lower ignition temperature
than the coal, so when the coal enters the, furnace, the volatiles are driven off
and ignite first. The heat from the burning.volatiles heats up the rest of the
»
coal to its ignition temperature. »
Combustion of the Volatiles
The volatiles will produce a different kind of flame depending on
how rapidly they are heated and how they are mixed with oxygen.
For example, if the volatiles are heated very rapidly and are slow to
mix with the oxygen, they produce a yellow flame. This is because the high
temperatures split the hydrocarbon molecules apart (called cracking by chemists)
into separate carbon and hydrogen molecules. The hydrogen burns almost instantly
to form water vapor, but the carbon is slower to combine with the oxygen. The
tiny carbon particles glow or incandesce until burned, giving the flame its yellow
appearance. If these carbon particles leave the flame without being burned,
they are called soot.
KVB4-15900-560
16
-------
Another kind of flame is produced when the volatiles are well-mixed
with oxygen and are heated more slowly. Under these conditions, the hydrocarbon
molecules combine with oxygen first and then split apart into water vapor and
carbon dioxide. Because there is no free carbon floating around, there is no
soot and no yellow flame. The flame produced is blue.
The blue flame is best, because it is the cleanest burning. However,
in coal combustion, both combustion sequences are always present and the coal
flame is usually yellow-orange in appearance.
Anyone who has played with a bunsen burner knows how to produce both
kinds of flames. If the air ports are closed at the base of the burner, a yellow
sooty flame is produced because the hydrocarbons split apart before they burn.
But when the air ports are opened so that the gas and air are premixed before
they reach the flame, the flame is blue and produces no soot.
Combustion of the Coke
What remains after the volatiles have been driven off is primarily
carbon and ash. This is called coke. The carbon is called "fixed carbon"
because it wasn't driven off with the volatiles. Fixed carbon does not vaporize
before it burns; it would require 6300°F to vaporize the carbon in the coke,
whereas furnace temperatures are less than 3200°F. Instead, oxygen attaches to
the surface of the coke and breaks away as carbon-oxygen compounds.
If there is plenty of oxygen available, carbon dioxide (CC^) is formed
at or near the surface of the coal and there is no flame. Like a good charcoal
fire or a smoldering log, combustion takes place very near the surface.
If there is not enough oxygen to go around, some of the carbon is only
partially oxidized. That is, it only reacts with one oxygen atom instead of two,
forming carbon monoxide (CO). This is bad for two reasons. It is a waste of
fuel because carbon releases less than 1/3 of its energy when it reacts with only
one oxygen atom; and secondly, the carbon monoxide formed is a safety and health
hazard.
Fortunately, most of this carbon monoxide will be burned to carbon
dioxide as it passes up through the flame zone created by the other burning
volatiles.
KVB4-15900-560
17
-------
REQUIREMENTS FOR COMPLETE COMBUSTION
Four requirements must be met before complete combustion will take place.
These are proper fuel-air ratio, turbulence, temperature, and time. The last
three are commonly called the 3 T's of combustion.
Fuel-Air Ratio
A combustion engineer can calculate the exact amount of air required
to burn any coal if he knows the chemical analysis of that coal. This "Theoretical
Air" (sometimes called stoichiometric air) would contain the exact amount of
oxygen required to burn all the combustibles in the coal.
In actual practice, the fuel always needs more than the theoretical
amount because mixing of the fuel and air is not perfect. Stokers generally
require 30% to 50% more air than the theoretical minimum in order to prevent
incomplete combustion at high loads. At low loads, an even higher percentage of
"excess air" is required.
A proper fuel-air ratio is necessary to support complete combustion.
If there is too little air, the result is smoke, carbon monoxide and clinkering
on the grate. If there is too much air, the result is low boiler efficiency
and cooling of the flame. The ideal is to operate with as little air as
possible without creating excessive smoke, carbon monoxide, or clinkering.
Turbulence
It does no good to have a proper fuel-air ratio if the air is not properly
mixed with the fuel. It often happens that streams of fuel-rich gases will rise
in one area of the fuel bed while streams of air-rich gases will rise in another.
Without turbulence to evenly mix the combustible gases with the air, combustion
will be incomplete. The result will be excessive smoke, high carbon monoxide
emissions, and low boiler efficiency.
Overfire air jets are installed on most modern stoker equipment to provide
this turbulence. Arches are used in some boiler designs to direct the hot volatile
gases to the flame zone. This is another means of providing mixing, or turbulence.
KVB4-15900-560
18
-------
The fixed carbon on the grate also requires the movement of air. Without
this movement, a layer of carbon dioxide and carbon monoxide forms around the
coal making it difficult for oxygen to penetrate. Air movement strips away this
gas layer and provides a fresh supply of oxygen. Have you ever noticed how blowing
on a charcoal fire increases the combustion dramatically? This illustrates the
same principle.
To insure an even and constant distribution of air to the coals, grate
air holes must be kept unplugged, warped or broken grate sections must be replaced,
and clinkers must be broken up. Also, coal must be evenly distributed on the
bed because the air will flow through the areas of least resistance and starve
the areas of most resistance. This is very important.
Ignition Temperature
Before combustion begins, the fuel must be heated to its ignition
temperature. This is the temperature at which more heat is generated by the
chemical reaction of combustion than is required to sustain ignition.
As an example, consider a lump of coal held in your hand. This coal is
in contact with the air and is reacting with oxygen in the air. This reaction
is giving off heat. But, the reaction is extremely slow at room temperature
and the heat is carried away as soon as it is formed. So, the lump of coal
never heats up and the chemical reaction remains imperceptably slow.
Now, consider this same lump of coal inside a coal pile. Again, it
reacts with the oxygen which surrounds it inside the pile. But now the lump of
coal is insulated by the surrounding coal in the pile. Under these conditions,
heat from the slow oxidation of the coal may be generated faster than it can be
carried away because of the insulating effects of the surrounding coal. When
this happens, the lump of coal becomes slightly warmer and the rate of oxidation
increases slightly. You can see what happens next, the coal gets hotter and the
reactions get faster until the ignition temperature is reached and a fire begins
in the coal pile. This same reaction can occur with oily rags placed in a
confined container. It's called spontaneous combustion.
KVB4-15900-560
19
-------
In a coal-fired stoker, the operator is concerned with maintaining
complete combustion. If a flame is cooled too fast, combustion will be incomplete,
The flame will be quenched before all the chemical reactions have taken place.
The result is smoke from unburned carbon particles, and high concentrations of
carbon monoxide.
One way a flame is cooled too fast is when it touches (or impinges on)
a cold water wall. Flame impingement is prevented by adjusting overfire air
jets to push the flame away from the water wall, or by adjusting the undergrate
air zones, or by changing the coal distribution pattern in the case of spreaders.
Very high excess air can also lower the temperature enough to cause incomplete
combustion.
Time
Combustion is not instantaneous. It takes time for the oxygen molecules
to collide with (and react with) the carbon and hydrogen molecules. The time
required is less if turbulence is present, if temperatures are higher, and if
the fuel-air ratio is proper. Time and temperature go hand-in-hand. The volatile
gases must be above their ignition temperature for sufficient time to complete
combustion. If the flames impinge on the water walls before they have had time
to complete combustion, the result is smoke and high carbon monoxide emissions.
It also takes time for the fixed carbon on the grate to burn. The time
required is shortened when the excess air is increased. Grate speed (on traveling
grate units) and undergrate air distribution are adjusted to allow the fixed
carbon to burn to completion.
PRODUCTS OF COMBUSTION
There are eight common products of combustion which make up the flue
gas of all coal-fired stoker boilers. Each one is discussed below. The first
two, carbon dioxide and water vapor, are harmless gases and necessary products
of combustion. The remaining six are always present to some degree, but they
should be minimized because they either reduce boiler efficiency or they are
considered pollutants.
KVB4-15900-560
20
-------
Carbon Dioxide (CO2)
This is a harmless gas which results from the complete combustion of
carbon. The chemical reaction is: C + 02 -»• C02 + 14,100 Btu per pound of carbon
burned. This reaction is responsible for 78% of the heat released from a typical
coal.
Water Vapor (H2O)
This harmless vapor results from the combustion of hydrogen. The chemical
reaction is: 2H2 + 02 -»• 2H2O + 61,100 Btu per pound of hydrogen burned. This
reaction is responsible for 22% of the heat released from a typical coal.
Nitrogen (N2)
Most of the nitrogen in the air is carried through the boiler without
reacting with oxygen. It makes up about 75% of the flue gas by volume. The
added weight of the nitrogen increases the amount of heat carried out the stack
and in this way reduces boiler efficiency. It also adds to the volume of flue
gas and wastes fan power. For these reasons, nitrogen should be kept at a
minimum by keeping excess air at a minimum.
Oxygen (O?)
There is always some oxygen left over after combustion. In stoker-
boilers, the operator is doing well to keep the oxygen in the 5-7% range. This
unused oxygen reduces the efficiency of the boiler in the same way that nitrogen
does. Every extra pound of oxygen brings with it 3.3 extra pounds of nitrogen,
and this "excess air" absorbs heat which could otherwise have been converted to
steam, and carries it out of the stack.
Carbon Monoxide (CO)
This gas results from incomplete combustion of carbon: it's wasted fuel
going out the stack. When one carbon atom combines with only one oxygen atom, it
releases only 28% of its heat. The other 72% is lost. Carbon monoxide is also
a health hazard when inhaled in high enough concentrations, and a safety hazard
because it can form explosive mixtures in high concentrations.
KVB4-15900-560
21
-------
SOx; Sulfur Dioxide (SO2) and Sulfur Trioxide
This gaseous emission is formed from combustion of sulfur in the coal.
The chemical reactions release heat which add slightly to the heating value of
S + O2 ->• SO2 + Heat
2 S + 3O2 -»• 2SO3 + Heat
a typical coal. Unfortunately, these sulfur oxides are harmful to plants and
animals. The SO3 combines readily with water vapor to form sulfuric acid which
is very corrosive, and which contributes to the acid rain problem.
One way to reduce this emission is by purchasing a lower sulfur coal.
Another way is to install a sulfur scrubber. Fuel additives have been used to
retain some of the sulfur in the ash and thus reduce the SOx emissions. Washing
the coal may also lower its sulfur content and thus reduce SOx emissions.
NOx; Nitric Oxide (NO) and Nitrogen Dioxide (NO2)
This gaseous emission can be partially controlled in stokers by reducing
the excess air. Nitrogen oxides are formed from both the nitrogen in the fuel
and the nitrogen in the air. These chemical reactions add nothing to the heating
value of the fuel.
2 N + 02 -*• 2 NO
N + O2 •»• NO2
Unfortunately, it doesn't take much NOx to form photochemical smog, so this
pollutant is highly undesirable. It also contributes to the acid rain problem.
Particulate Matter
Particulates are solid particles of flyash carried along with the flue
gas. They may contain some carbon which when carried out the boiler reduces the
boiler efficiency.
Particulate matter can be reduced by proper stoker-boiler operation.
Mechanical dust collectors, baghouses, and electrostatic precipitators are also
used to collect particulate matter before it goes out the stack.
SUMMARY
The operator's job will be easier and more enjoyable if he understands the
combustion process. The more he knows about combustion, the better control he will
have over it.
22 KVB4-15900-560
-------
SECTION 4
BOILER EFFICIENCY
Most stoker fired boilers are between 65% and 85% efficient in converting
the coal's energy into steam. This means that much of the coal's energy is wasted.
Some of this waste is unavoidable/ as we will see, but some of it can be avoided
if the operator understands how it occurs.
"Heat loss" is the term used to describe the way energy is wasted.
Figure 13 illustrates the major heat losses- in stoker-boilers. This section
of the manual describes the major heat losses and explains how to reduce them.
First, however, we will show you how boiler efficiency is determined by the
measurement of heat losses.
CONSERVATION OF ENERGY
On of the laws of nature states that energy is conserved. It may
change form, as from chemical energy to thermal energy, but you always end up
with-as much as you started with. So in a coal fired stoker-boiler, if you add
up the energy in the steam, the energy in the flue gas, the energy radiated from
the boiler and all the other forms of energy leaving the boiler, they will
exactly equal the energy in the coal burned. Another way of stating it is like
this:
Energy in Coal = Energy in Steam + Energy in Heat Losses
BOILER EFFICIENCY
Boiler efficiency is the percentage of the coal's energy which is con-
verted to steam energy. The most accurate way of determining boiler efficiency
in stoker-boilers is to use what is known as the heat loss method. (Ref #16) In
this method you simply measure the individual heat losses (expressed as percent
of heat input) and subtract them from 100%. This is possible because energy is
conserved.
Boiler Efficiency = 100% - Heat Losses
KVB4-15900-560
23
-------
Stack Gas
Heat Loss
Slowdown
Heat Loss
Combustible
Heat Loss
Figure 13. Major Heat Losses in Stoker Boilers
KVB4-15900-560
24
-------
STACK GAS HEAT LOSS
The largest loss of energy in a stoker-fired boiler is the energy in the
flue gas going out the stack, which might account for as much as 30% of the fuel
input in the worst cases. This is called the stack gas heat loss. When engineers
measure this heat loss, it is broken down into three components. These components
are heat loss due to dry gas, heat loss due to moisture in the fuel, and heat
loss due to H2O from the combustion of H2• As far as the operator is concerned,
these three can all be lumped into one category: stack gas heat loss.
The biggest gains in boiler efficiency can be obtained by minimizing
the stack gas loss. This loss depends on the temperature and the volume of gas
leaving the boiler, so a reduction in either one of these will reduce the heat
loss.
The practical minimum flue gas temperature limit is about 300°F. At
lower temperatures, sulfuric acid vapor in the flue gas condenses on cold metal
surfaces and causes severe corrosion. Therefore, some stack gas heat loss is
unavoidable. To eliminate the stack gas heat loss altogether, you would have
to reduce the stack gas temperature to the temperature of the air around the
boiler. Practically speaking, this is impossible.
There are three basic strategies for minimizing the stack gas heat
loss. They are:
1. Minimizing excess air
2. Keeping heat transfer surfaces clean
3. Adding flue gas heat recovery equipment where justified
When excess air is reduced, it reduces the volume of flue gas leaving
the boiler. It also reduces the temperature of the flue gas because the gas
velocities are reduced and the flue gas spends more time in the boiler where
heat can be absorbed. As a result of reducing the volume and temperature of
the flue gas, the stack gas heat loss is reduced and the boiler efficiency is
increased. As a rule of thumb, boiler efficiency can be increased one percent
for each 15 percent reduction in excess air, 1.3% reduction in 02, or 40°F
reduction of stack gas temperature. What is one percent of your annual fuel bill?
KVB4-15900-560
25
-------
Keeping heat transfer surfaces clean must also be considered when
operating the boiler. Ash deposits on water walls (slagging) and on boiler
tubes (fouling), and scale deposits on the waterside tube surfaces act as
insulation. This reduces the amount of heat the boiler water absorbs from the
flue gas. As a result, the flue gas temperature is high and the boiler efficiency
is low. Fouling and slagging are controlled by proper use of soot blowers,
overfire air and excess air. Scale deposits are controlled by feedwater treatment
and proper use of blowdown.
The third strategy for minimizing stack gas heat loss is to install
additional heat recovery equipment such as an air heater or economizer. If the
boiler's flue gas temperature is greater than 450° when tuned-up, it is worthwhile
considering one of these devices. An engineering study will be required to
determine if such a device will be cost-effective on your boiler.
COMBUSTIBLE HEAT LOSS
The second largest heat loss in stokers is due to unburned fuel. This
is called the combustible heat loss, and is often greater than 5% of the coal's
energy. It occurs in three major ways:
1. Carbon in the bottom ash
2. Carbon in the flyash
3. Combustible gases in the flue gas
Carbon in the bottom ash results when coal is dumped into the ash pit
before it has been completely burned. The operator should take care to adjust
the stoker so that the carbon is completely burned out. On traveling and chain
grate stokers, this is done by properly adjusting the coal gate position, grate
speed, and the undergrate air flow. On spreader stokers, the operator must
adjust the grate speed, undergrate air flow, and the coal feeders if
necessary. Experience will show which stoker adjustments work best.
Recent tests on 18 stokers gave the following range of heat losses due
to combustibles in the bottom ash: (Ref #1-12)
Heat Loss Due to Combustibles in the Bottom Ash, Percen-
Lowest Highest Average
Spreader Stokers 0.0% 3.4% 0.9%
Overfeed Stokers 0.4% 8.1% 2.4%
Underfeed Stokers 1.2% 3.9% 3.2%
KVB4-15900-560
26
-------
Carbon in the flyash is the result of small coal particles being
blown off the grate or, in the case of spreader stokers, small particles being
caught up (or entrained) in the gas flow before they land on the grate. This
is also called flycarbon, carbon carryover, or combustibles in the flyash. To
reduce this heat loss, you must reduce the particulate loading. Increasing the
overfire air has been found to be effective in some cases. Reducing the excess
air may also work in some cases. And, a coal with fewer fines or less ash may
help.
Tests on 18 stokers gave the following range of heat losses due to
combustibles in the flyash: (Ref #1-12)
Heat Loss Due to Combustibles in the Flyash
Lowest Highest Average
Spreader Stokers 0.5% 9.2% 4.4%
Overfeed Stokers 0.3% 1.1% 0.5%
Underfeed Stokers 0.1% 0.2% 0.1%
Combustible gases are volatiles which did not burn to completion. The
most commonly measured combustible gas is carbon monoxide (CO). Carbon monoxide
is formed when the excess air is too low in some area of the grate, or when the
flame impinges on a cold water wall. If the coal is evenly distributed on the
grate, and if the undergrate air and overfire air are properly adjusted, this
heat loss is minimized. On most stokers, the carbon monoxide concentration can
be maintained below 400 ppm (.04%). This is about a .2% heat loss.
RADIATION HEAT LOSS
Some of the heat of combustion escapes through the walls of the furnace
without being absorbed by the boiler water. This energy loss is called the
radiation heat loss. Some radiation heat loss is unavoidable. If there were
none, the outside surfaces of the stoker-boiler would be the same temperature
as the surrounding air. Most stoker-boilers are properly insulated when installed.
It is necessary to maintain the insulation in good condition. This includes all
hot surfaces: water walls, ducting upstream of heat recovery devices, and steam
pipes.
KVB4-15900-560
27
-------
A properly insulated boiler has the following radiation heat losses
at full load. Note that larger boilers lose a smaller fraction of their heat
through radiation from hot surfaces.
Radiation Heat Loss
200,000 Ib/hr boiler .5%
100,000 Ib/hr boiler .7%
50,000 Ib/hr boiler .9%
20,000 lb.hr boiler 1.0%
SLOWDOWN HEAT LOSSES
There are other heat losses, but they are usually quite small. One
worth mentioning, however, is blowdown. A certain amount of blowdown is necessary
to maintain control of dissolved solids in the boiler water. Excessive blowdown,
however, is a heat loss because it is energy being thrown away. One way to
reduce this heat loss is to install a continuous blowdown heat recovery device.
These devices are now economical for blowdowns as low as 500 Ib/hr. The other
way to minimize blowdown heat loss is to establish a good feedwater treatment
program and to check the dissolved solids level regularly. In this way you
can reduce the amount of blowdown required.
SUMMARY
All of these heat losses taken together add up to between 15% and 35%
of the coal's energy. An operator can usually save enough on fuel bills to
cover his salary by understanding these heat losses and operating the stoker-
boiler at peak efficiency.
KVB4-15900-560
28
-------
SECTION 5
GUIDELINES FOR CLEAN AND EFFICIENT BOILER OPERATION
This section discusses ways in which an operator can obtain peak boiler
efficiency from his stoker-boiler while maintaining pollutant emissions within
allowable limits. The material in this section does not replace the manufacturers
operating instructions, but supplements it. Always use common sense when applying
these, or any, guidelines.
BOILER MAINTENANCE
At most of the larger installations, the boiler-operator is not respon-
sible for performing maintenance tasks. However, he is always responsible for
reporting problem areas requiring maintenance. The following are common problem
areas which directly affect boiler efficiency.
Undergrate Air Distribution
For peak efficiency the undergrate air must be properly distributed to
the coal. Replace worn, broken, or warped grate sections. Replace worn air
seals which allow undergrate air to short circuit the grate. Repair or replace
undergrate air zone dampers which prevent proper control of the air distribution.
Finally, repair the coal feed mechanism if it does not distribute an even bed
of coal to the grate.
Air Infiltration
For peak efficiency, air infiltration to the furnace must be minimized.
The boiler economizer and air heater casings should be tight, with no air leaks.
Seals between the stoker and the boiler must be tight. Replace warped or cracked
access doors which do not seal properly. Replace missing sight glass in view
ports, patch leaks in ductwork, especially when upstream of an air heater or
economizer.
KVB4-15900-560
29
-------
Insulation
Considerable energy is wasted if hot surfaces are not properly in-
sulated. For example, the heat loss from 100 feet of bare 2-inch pipe carrying
saturated steam at 150 psig is equivalent to a fuel loss of one ton of coal
every 12 days. If that were 12-inch pipe and 250 psig, the fuel loss would be
one ton of coal every 2 days. Repair damaged or missing insulation and re-
fractory on all hot surfaces.
Steam Leaks
An obvious waste of energy results from the numerous steam leaks at
pipe joints, flanges, valves and unions. Less obvious are the steam losses from
malfunctioning steam traps. It pays to repair steam leaks as soon as possible.
Soot Blowers
Soot blowers should be checked for proper operation. If ash deposits
are allowed to accumulate on boiler tubes, less of the coal's heat will make
steam and more will be lost out the stack. It has been said that 1/8 inch of
soot equals one inch of insulation.
Instrumentation and Controls
Pressure gauges, draft gauges, temperature indicators and flow indicators
are the eyes of the operator into the stoker-boiler. These should be routinely
calibrated and serviced.
Boiler controls are required to maintain optimum firing conditions. If
the controls are not working properly, the boiler's efficiency will suffer.
Check controls for proper movement of valves, excessive play in linkages, ade-
quate instrument air pressure, regulators, unnecessary cycling of firing rate,
and proper operation of all safety interlocks and boiler trip circuits.
THE OPERATORS'S LOG
It is the operator's responsibility to maintain a complete log of panel
board data and significant events. This data is used by the plant engineer to
detect deterioration in stoker-boiler performance. For example, if the stack
KVB4-15900-560
30
-------
gas temperature creeps upward with time, it may mean a slagging or fouling problem,
or a problem with the excess air. Other trends may indicate other problem areas
requiring attention. The number of items on the log sheet and the frequency with
which they are recorded depends on the size and complexity of the boiler. Figure
14 illustrates a high pressure boiler log sheet for recording twice daily
readings. Figure 15 illustrates a log sheet for recording hourly readings.
Whatever size the boiler, the most important efficiency-related items to
record are the steam flow, flue gas temperature, and excess air. It is highly
recommended that all boilers be equipped with a stem thermometer or thermocouple
for measuring flue gas temperature after the last heat recovery device. It is
also recommended that an oxygen monitor or carbon dioxide monitor be installed for
determining excess air. These devices will quickly pay for themselves in energy
savings.
IOILER NO.
CHECK OR TEST AND RECORD TWICE DAILY
REMARKS
MON A'M'
P.M.
TUES A'M-
P.M.
A.M.
WED
P.M.
A.M.
THUR
P.M.
A.M.
m
P.M.
A.M.
SAT
P.M.
A.M.
SUN
P.M.
Figure 14. High Pressure Power Boiler Log Sheet for Twice Daily
Readings (Compliments of the Hartford Steam Boiler Inspection
and Insurance Company).
KVB4-15900-560
31
-------
12:00
100
2:00
3:00
4:00
S:OO
6:00
7:00
8:00
9:00
10:00
11:00
12:00
1:00
2:00
3.-OO
4:00
S:00
6:00
7:00
8:OO
9:00
10:00
UKX)
Figure 15. High Pressure Boiler Log Sheet for 24-Hourly Readings
(Compliments of the Hartford Steam Boiler Inspection
and Insurance Company).
OPTIMIZING THE EXCESS AIR
Optimizing the excess air is the easiest way to make substantial improve-
ments in boiler efficiency. All that is required is some initiative on the part
of the operator, and the appropriate instruments for monitoring excess air, incom-
plete combustion and stack gas temperature. Careful observation and thoughtful
action can provide efficiency increases on the order of one-to-four percent.
Optimum excess air is illustrated in Figure 16. When excess air is
reduced on a stoker, the stack gas heat loss drops until a point is reached where
there is no longer enough oxygen for complete combustion. At this point there is
a rapid increase in smoke and carbon monxide, often accompanied by severe
clinkering. The excess air levels at which the smoke and CO begin to increase
rapidly are called the "smoke limit" and the "CO limit". This point is the minimum
KVB4-15900-560
32
-------
excess air level and Is the most efficient place to operate. Unfortunately,
to operate here is to flirt with disaster. The excess air could easily swing
below the smoke and/or CO limit.
Therefore, the operator must allow for a safety margin in the excess air
level so that normal swings in the load, coal sizing, or coal segregation do not
produce undesirable firing conditions. The size of the margin is determined by
trial and error, and depends on how stable the load is, and how sophisticated the
combustion controls are. The safety margin typically ranges from 5% to 20% ex-
cess air (0.5-1.5% O2). The optimum excess air is then established at this point.
The optimum excess air must be re-established at several different firing rates.
This is because more excess air is required at reduced loads than at full load.
t
(U
•0
•a
•rH
X
0
u
4J
C
0)
o
Optimum
Excess Air
The following limits have
been found useful when
testing stokers:
CO: 400 ppm
Smoke: 20%
Limit
Percent Excess Air -*•
Figure 16. Carbon Monoxide and Smoke vs Excess Air. This Figure
Illustrates the use of a Safety Margin to Set an Optimum
Excess Air Level.
KVB4-15900-560
33
-------
Measurement Techniques
To tune the boiler for optimum excess air, three basic measurements are
required. They are:
1. 02 or CC>2 for determining operating excess air levels.
2. CO and visual observations for detecting the minimum excess
air limit.
3. Stack gas temperature for determining the stack gas heat loss.
Excess air can be determined from Figure 17 if you know either the per-
centage of oxygen (02) or the percentage of carbon dioxide (CC^) in the flue gas.
Portable electronic and chemical analyzers are available for making these measure-
ments at low cost if you are not already so equipped.
An alternate method for determining excess air is given in Figure 18.
This chart is especially useful when using an Orsat-type analyzer where ©2 t C®2'
CO, and N^ are all determined simultaneously. On this chart, excess air is equal
to "total air" minus 100%.
03
(0
CM
•H
CN
8
CN
o
-P
0)
O
20
40 60 80
Percent Excess Air
100
120
Figure 17.
Combustion Chart for Determining Excess Air from either Flue
Gas Oxygen or Carbon Monoxide (Dry Basis) while Firing a
Bituminous Coal.
KVB4-15900-560
34
-------
.
s7yvyvv\/\ v
yyMJAAWAAAiV^nrA\n^nr¥WvVWv\Ai\ L
YWVWYWVYYWW^(Vv^VW^\VxWx/x
••ri^*—htlaABlMfc^bMUM»lMlhHB«*»«MMMB>l|^M
-------
Carbon monoxide (CO) can be measured with an Orsat-type analyzer down
to about 0.1%. However, this is not sensitive enough for an accurate determin-
ation of the minimum excess air limit. If at all possible, use an analyzer
with a minimum detection limit of at least 0.01%, or 100 parts-per-million (ppm) .
Visual observations include clinkering and slagging tendencies in the
furnace, and smoke at the stack. If the stack is not equipped with an operating
smoke meter for measuring opacity, it may be helpful to use a Ringlemann chart
to determine the opacity.
Location of the flue gas sampling site can be as important as the
selection of the proper measurement device. On negative-draft boilers, it should
be upstream of the air preheater, if one is installed, or upstream of any known
air leaks. This is because air leakage into the gas ducts can dilute the flue
gas and resultant measurements won't give a true indication of furnace conditions.
Sample locations immediately downstream of bends, dampers, or induced-
draft fans should be avoided. Gases in such areas can stratify or form pockets,
leading to errors, especially when samples are withdrawn from a single point in
the duct.
• When a single-point sample probe is to be used, compare readings at
»
several points in the duct first, to find the most representative probe location.
When existing ports are not satisfactory, drill or cut out new ports. Remember,
unless truly representative samples are obtained, your testing program will be
of little value.
Flue gas temperatures are also subject to stratification in ducts, and
a representative location for thermometers or other temperature sensors should
be verified by trying several locations. Consult the boiler manufacturer for
recommended location.
Efficiency Improvement Procedures
The boiler should be inspected prior to determining the optimum oxygen
operating level. The various items to check are summarized above in the sub-
section entitled "Boiler Maintenance". The boiler manufacturer should be
consulted for a more complete list reflecting your particular equipment.
KVB4-15900-560
36
-------
Once the boiler has been inspected and is in good mechanical condition,
the step-by-step procedures for minimizing flue gas oxygen may begin. The pro-
cedure is as follows:
STEP-BY-STEP PROCEDURES FOR MINIMIZING FLUE GAS OXYGEN
1. Bring the boiler to the test firing rate and put the combustion
controls on manual. Make sure all safety interlocks are functioning
properly.
2. After stabilizing, observe flame conditions and take a complete
set of readings (02 or COo, stack gas temperature, CO and/or
opacity).
3. Increase air flow to the furnace by about 1% 02 allowing time to
stabilize. Then take another set of readings.
4. Reduce the air flow in small steps while observing stack and flame
conditions. Allow the unit to stabilize following each change
and record the data.
5. Continue to reduce the air flow until a minimum excess air condition
is reached as indicated by smoke, a sudden rise in CO, or other
visible deterioration in conditions.
6. Establish a safe margin in excess air above the minimum and
reset the combustion controls to maintain this "optimum" level.
7. Develop a CO or smoke versus excess air characteristic curve
similar to Figure 16 using the data obtained from the test.
8. Compare the minimum excess air value to the predicted value
provided by the stoker and/or boiler manufacturers. High
excess air levels should be investigated (see the paragraphs
entitled "Boiler Maintenance" and "Fine Tuning").
9. Repeat Steps 1-8 for each boiler load to be considered. Some
compromise in optimum excess air settings may be necessary since
control adjustments at one firing rate may affect conditions at
other firing rates.
10. After these adjustments have been completed, verify the operation
of these settings by observing normal load swings. If undesirable
conditions are encountered, increase the safety margin.
The data obtained under Steps 2 through 5 will look something like that
shown in the following table.
KVB4-15900-560
37
-------
EXAMPLE OF EFFICIENCY IMPROVEMENT TEST DATA
Stack Gas
Step 2
Step 3
Step 4
Step 5
Step 6
(a)
(b)
(0
(d)
(e)
% o2
8.9
10.0
8.3
7.5
6.8
6.0
5.2
4.8
6.6
CO, ppm
105
130
95
100
158
270
612
1050
180
Temperature, °F
472
480
463
461
456
450
445
442
455
In this example, the baseline or as-found ©2 was 8.9%. The air flow was first
raised and then lowered in steps until carbon monoxide exceeded 1000 parts per
million. As the test proceeded, the carbon monoxide data were plotted as a
function of ©2 as shown in Figure 19.
»
The carbon monoxide limit is taken to be 400 ppm. Therefore, the minimum
flue gas oxygen operating level is 5.6%. If we select a 1% oxygen safety margin,
then the optimum oxygen operating level is 6.6%. We adjust the boiler controls
to maintain this oxygen level and record one more set of data as shown in Step 6
of the above table.
Next, we compare our operating level with that recommended by the
stoker-boiler manufacturer. We note that they recommend 40% excess air. Refer-
ring back to Figure 17, we see that 40% excess air is about 6.2% O2. This is
reasonably close to the optimum operating level we determined by test, and we
are now satisfied that our boiler is operating as it should. Step 8 is now
complete.
KVB4-15900-560
38
-------
1000
800
£
H
O 600
I
2
§
400
ttr
ojniuitt
i i
•trtir
200
4 6
EXCESS OXYGEN, %
10
Figure 19. This is a Plot of the CO - 02 Data Given in the Example
KVB4-15900-560
39
-------
To find out how much we improved the boiler efficiency, we refer to
Figure 20. This plot relates stack gas C>2 and stack gas temperature to stack
gas heat loss for a typical bituminous coal. It may be used with most coals
to find approximate stack gas heat loss savings. Using this plot we obtain
the following results:
Stack Gas
Stack Gas Heat Loss
02, % Temperature, °F From Figure 20
Baseline Test 8.9 472 17.8%
Optimum Test 6.6 455 15.1%
EFFICIENCY GAIN 2.7%
To obtain the percent savings in the annual fuel bill, we divide the
efficiency gain by the boiler efficiency and multiply by 100.
2.7 Efficiency Gain , „„ _ ,_
———— —=•£•:—: x 100% = 3.38% Fuel Savings
80% Boiler Efficiency
If the annual fuel bill is $1,000,000 per year, then the cost savings
is $33,800 annually. Each situation will differ, but in all cases, it is well
worth the effort to minimize the excess air.
Fine Tuning
If the optimum excess air level determined by test is higher than the
manufacturers recommended level, the stoker should be re-examined. It is some-
times possible to lower the CO or smoke limit, thus allowing greater efficiency
gains. The usual procedure involves one or more of the following actions:
1. Minimize coal segregation to the stoker.
2. Adjust stoker for uniform coal distribution on the grate.
3. Adjust stoker for balanced undergrate air flow through the grate.
4. Adjust overfire air to improve turbulence and hold flame front
off the water walls.
5. Reduce the coal fines if they are excessively high.
6. Reduce air infiltration through cracks in the casing and access
doors.
KVB4-15900-560
40
-------
EH
D
Z
H
i/l
3
I
SB
u
X!
O
<
EH
W
100
200
300 400 500
STACK GAS TEMPERATURE, °F
600
700
Figure 20. Stack Gas Heat Loss as a Function of Stack Gas Temperature and
Stack Gas Oxygen for a Typical Bituminous Coal. (Coal Composition
by Weight: H20-5%, C-73%, H-5%, N-l.4%, S-l.5%, 0-7.1%, Ash-7%,
13,000 Btu/lb., Ambient Air Temperature - 80°F)
KVB4-15900-560
41
-------
Here is a true example of a boiler requiring fine tuning. It is a
182,000 Ib/hr spreader stoker belonging to a midwestern pulp and paper company.
The full load smoke limit on this unit was found to be at 50% excess air, yet the
manufacturer claimed the unit was capable of operation at 30% excess air. Upon
investigation, it was discovered that coal was being segregated in the hopper
so that most of the coal fines were being fed to one section of the grate. As
a result of this coal size segregation, the excess air was low in some areas of
the grate and much higher in the other areas. The areas of low excess air
reached the smoke limit long before the average excess air reached its design
levels.
f
Maintaining Optimum Excess Air
It is easy to demonstrate optimum boiler efficiency during a test. It
is much harder to maintain optimum efficiency day after day. Maintaining optimum
boiler efficiency requires a conscientious effort by the boiler operators and
their supervisors.
During the first month or two you should pay special attention to
combustion conditions. Watch for problems with clinkering, smoke, excessive
carbon monoxide and slag buildup. Check the excess air level and the stack
gas temperature regularly. Take corrective action if conditions deteriorate.
Keep on top of boiler maintenance requirements. Thoroughly inspect the boiler
during the next shutdown.
One of the best aids an operator can have in maintaining low excess
air is a stack gas sampling system which continuously monitors oxygen and, if
possible, carbon monxoide or combustibles in the flue gas. There are several
reliable 62 and CO monitors on the market, and they will usually pay for them-
selves in fuel savings over a short period of time. If you don't use continuous
monitors, the excess air level should be routinely checked with an Orsat, or
other portable gas sampling device.
Normal Ranges of Excess Air
If you don't know what the design excess air level is for your stoker,
you might be interested in some rule-of-thumb figures. Spreader stokers should
be able to operate at or near 30% excess air at high firing rates. Other types
KVB4-15900-560
42
-------
of stokers should be able to operate at or near 50% excess air. These are only
general guidelines. Smaller stokers tend to require more excess air than larger
ones, and the stoker's state of repair will make a difference. The quality of
coal fired may also influence excess air requirements.
Recent tests on six spreader stokers and five mass-fired overfeed
stokers produced the excess air operating levels shown in Figures 21 and 22.
These trend lines represent average as-found levels and are not necessarily the
optimum excess air levels. Note that in every case more excess air was required
as the firing rate was lowered.
Similar profiles can be produced for your stoker for the optimum excess
air levels at all firing rates by following the efficiency improvement procedures
given earlier. They would be a very helpful guide to operators who have the
means to measure the excess air. If 02 or CC>2 is used on the plot instead of
excess air, they will be more easily compared to the direct readings.
How Excess Air Effects Emissions
When the excess air is optimized, some pollutant emissions decrease.
Thus, you obtain two direct benefits: Energy savings and cleaner stack gases.
The emission which decreases the most is nitric oxide (NO), a pollutant which is
responsible for producing photochemical smog among other things. Nitric oxide
emissions drop by nearly 0.03 lb/10^Btu for each 10% excess air drop. An example
of this is shown in Figure 23.
Carbon monoxide emissions are usually lowest at the optimum excess air
level. They increase slowly as the excess air goes up, and they increase rapidly
as the excess air goes below the carbon monoxide limit.
Particulate emissions are sometimes improved and sometimes unchanged by
reducing excess air. Reducing the excess air reduces the gas velocities in the
furnace and ductwork, and this In turn should carry less particulate material
off the grate and allow more particulate material to settle out before it is
emitted from the stack.
Finally, sulfur oxide emissions (SOx) are unaffected by changes in the
excess air. About 95% of the sulfur in the coal is converted to SOx no matter
how you operate the stoker-boiler.
KVB4-15900-560
43
-------
180
150.
120
CO
in
LU
O
90
Q_ .
60
30
1
20
40 60 80
PERCENT DESIGN CAPACITY
100
120
Figure 21. Excess Air Trends for Five Overfeed Stokers. The
Trend Lines Represent Average Excess Air Levels
Obtained over a Wide Range of Firing Rates.
(Ref #4, 8, 9, 10, 11)
KVB4-15900-560
44
-------
180
150
120
GO
C/>
UJ
£ 90
UJ
60
1
1
20
40 60 80
PERCENT DESIGN CAPACITY
100
120
Figure 22. Excess Air Trends for Six Spreader Stokers Obtained
over a Wide Range of Firing Rates. The Trend Lines
Represent the Average of a Large Number"of Tests.
(Ref # 1, 2, 3, 5, 6, 7)
KVB4-15900-560
45
-------
o
o
o
in
CD
§
OQ g
-1 CO
tij •
a
Si
i^ CNJ
CC
O
o
o.
O
-1 1 1 1
30. 60. 90. 120.
EXCESS flIR PERCENT
—i—
150.
Figure 23. The Relationship Between Nitric Oxide and Excess Air
on an Overfeed Stoker. (Ref #9)
OVERFIRE AIR
Overfire air has two main purposes in stoker-boiler operation. The
primary purpose is to promote turbulence in the flame zone so as to mix the
volatile gases with the air for better combustion. The secondary purpose is to
hold the flames away from the water walls so as to prevent premature cooling or
quenching of the flames. Recent tests have shown that increased use of overfire
air can also reduce particulate emissions. An example of this effect is shown
in Figure 24.
At high boiler loads, the overfire air should be set at a high level.
Reduce the overfire air pressure at low boiler loads. If in doubt as to how
much overfire air to use, you are usually better off to use more rather than
less. When the overfire air is increased, allow the undergrate air to decrease
so that the excess air remains low.
KVB4-15900-560
46
-------
Whenever carbon monoxide or smoke are present, try increasing the
overfire air pressure. This will sometimes clear up the problem and allow
you to operate at a lower and more efficient excess air.
On some stokers, there may be a problem with high overfire air pressures
if the resulting turbulence is lifting particulate matter off the grate. This
is very rarely a problem, but when it does happen, the overfire air pressures
should be reduced.
o
o
o
CO
_i o
o
• o
i— LO •
cc
-------
CINDER REINJECTION
Cinder reinjection, also known as flyash reinjection, is used primarily
on spreader stokers. Its purpose is to recover some of the energy in the flyash
by giving it a second chance to burn. The flyash from spreader stokers often
contains 50-80% carbon and can account for more than 5% of the coal's energy.
v
Incidentally, the percentage of carbon in the flyash of other types of stokers
is much less, and the amount of flyash collected is less. Therefore, it's not
worth installing cinder reinjection systems on non-spreader stokers.
On spreader stokers, the flyash collected in the boiler hopper is
usually reinjected, and the flyash collected in the mechanical dust collector
hopper and the economizer or air heater hopper is sometimes reinjected. The
operator should insure that the reinjection lines do not plug up. If they do,
they should be rodded open as soon as possible. Not only is energy wasted by
plugged lines, but if the hoppers are allowed to fill up with ash, that ash
will be blown out the stack and will increase the particulate emissions.
FIRING RATE
Most stokers are most efficient near full load. This is because stack
gas heat losses are high at low loads where more excess air is required.
Radiation heat losses are also higher at low loads. On the other hand, some
stokers, when operated at their full firing rate, have high combustible heat
losses due to high carbon carryover. On these units the efficiency drops off
slightly at full load. As a rule-of-thumb, peak boiler efficiencies are ob-
tained at about 80% of design capacity.
Some pollutant emissions also increase at high loads. Particulate
loading typically increases with load as shown in Figure 25. If the load is
unstable, as on swing load, particulate loading increases even more. Nitric
oxide emissions generally stay at the same level at all firing rates on
stokers, as do sulfur oxide emissions. Carbon monoxide emissions sometimes
increase at full load, but they also increase at extremely low loads.
For the most efficient and the cleanest stoker operation, sudden load
swings should be held to a minimum. When firing more than one boiler, the
bulk of the load should be carried by the most efficient unit(s).
KVB4-15900-560
48
-------
o
o
o
LO
CO
£8
x.
CD
_l O
O
• O
I—
DC in
-«
o_
S g
§2
LO
-bo
o
o
a
QD
O
o
o
CD
CD
o
o
20.0 40.0 60.0 80.0
PERCENT DESIGN CflPRCITY
100.0
Figure 25. Uncontrolled Particulate Loading as a Function of
Boiler Loading on a Spreader Stoker. (Ref. #2)
COAL PROPERTIES
Operators are generally not involved in obtaining coal supply contracts,
so they don't need to be experts on all the coal properties. However, the
operator is responsible for firing the purchased coal as efficiently and cleanly
as possible, and for informing his supervisors of coal related problem areas.
There are several coal properties which have a direct effect on stoker-
boiler emissions and efficiency. The operator should be aware of these
properties.
KVB4-15900-560
49
-------
Coal Ash
Coals which are higher in ash content tend to produce higher particu-
late emissions. This is only a generalization and it should not be assumed
that the particulate loading is directly related to the ash content.
The type of ash makes a difference. In recent tests on a traveling
grate overfeed stoker a washed coal and an unwashed coal from the same mine
were fired in the stoker. The unwashed coal had 10% ash, but when washed the
same coal had only 4% ash. In this case (Figure 26) there was a tremendous
difference in particulate loadings because much of the ash in the unwashed coal
was a clay-like material which was easily carried out of the furnace by the
flue gas.
In tests on other stokers, coals with different ash contents were
fired in the same stoker with very little or no change in particulate loading.
_3
t—
OQ
O
j
£
03
D
1—
DC
cr
Q_
o
UJ
— J
o
cc
I—
2
o
LJ
3
0
o
0
LD -
C\j
O
O
o
o -
0-J
0
O
O
LO-
^^
0
o
o
o -
*
o
o
o
in -
^-— — +
-^.^
UNWASHED COAL /
10% ASH. /
jr
/
/
/
/
/
/
/
H~ Q
rt\ ®
0 00 o^
" ' o
X
WASHED COAL
4% ASH
20.0 40.0 60.0 80.0
PERCENT DESIGN CflPflCITY
100.0
Figure 26. The Effect on Uncontrolled Particulate Loading of
Washing a Coal to Reduce its Ash Content. Data are
from an Overfeed Stoker. (Ref. #11)
KVB4-15900-560
50
-------
Coal Moisture
Coal has two forms of moisture. There is the inherent moisture which
is a part of the coal, and there is surface moisture which is due to rain or
conditions at the mine. You can't do anything about the inherent moisture,
but the surface moisture can sometimes be avoided.
Coal moisture causes two problems. If excessive, it may make the coal
hard to ignite, and it will always reduce the boiler efficiency.
Coal Sulfur
About 95% of the sulfur in the coal is converted during combustion to
SO2 and SG>3, commonly called SOx. The remaining 5% is retained in the ash.
Therefore, by burning a lower sulfur coal you reduce your sulfur oxide emissions.
Of course, there is another reason to burn a low sulfur coal, the sulfur
emissions are very corrosive if they condense on exposed metal parts. The 863
instantly combines with water vapor (H2O) to form sulfuric acid (H2SO4).
Coal Fines
The common definition of coal fines is the percentage of coal which
passes through a 1/4" screen. Too many coal fines can lead to high particulate
loadings because they are easily carried out of the furnace, and high combustible
heat losses because the particulate matter carries carbon out of the furnace
with it. High fines may also lead to severe clinkering problems.
When firing a high fines coal, make sure that the fines are evenly
distributed on the grate, and are not segregated in one area only. The manner
in which the coal is loaded into the hopper is important because it may lead
to stratification.
A coal which was low in fines when it left the mine may be high in
fines when it reaches the furnace because of all the handling it receives.
Coals which break up and produce fines more easily than others are called highly
"friable" coals. The American Boiler Mnaufacturers Association has published
guidelines for the recommended size consistency of coal for firing in different
types of stokers. These are presented in Figures 27, 28, and 29. Every
attempt should be made to operate within these guidelines.
KVB4-15900-560
51
-------
V
s
a.
Fuel to b» delivered ocroil ilokcr hopptr without six* segregatio
95
90
80
70
60
50
40
. 30
| 25
: 20
§ 15
10
8
6
4
3
8
**L
A
O O O O *O
-------
en
o
§
s.
Six* distribution of lower rank coals (Index 28 — 35) should fall nearer th* upper curve, and
six* distribution of higher rank coals (Index 40 — 50) should fall nearer the lower curve.
Fuel to be delivered across stoker hopper without six* segregation.
95
90
80
70
60
50
40
30
25
20
15
10
8
6
4
3
2
1
/
/
y
/
s
/
,
'
/
/
/
/
/I
'
/
A
'
/
/
'
/
/
/
/
/
/
/
/
1
J
'
/
{
1
I
/
'
/i
/
§O OOOO-OCNOO T I "f a>
O ID T O CN «— «— ,~X- ^- ~S- ~?r ~s-
CN •— I •—
US Std sieve designation
I Square mesh screen, inches
Figure 28. ABMA Recommended Limits of Coal Sizing for Overfeed
Stokers.
KVB4-15900-560
53
-------
PERCENT THROUGH SIEVE
Ul
Cd
cn
W)
O
O
I
U1
en
o
fi
n>
>£>
cn >
rt til
o p*
(D
cn CD
. o
o
tr1
H-
3
H-
rt
ui
O
H)
O
O
N
H-
HI
O
H
(D
&
(D
01
— — i\>roo> £ o* Q> --1 99 3?
O ,c
m 16
in
5 12
i 8
4
n M
1 *
m 3/4
S '*
•2 ,
Z '
2
S MI,
2
\
\
\
\
\
\
\
\
\
\
\s
^
V
\
N
^
\
\
\
\
\
\
\
x
\
x
\
X.
X
X
\
X
s
X
x
V
\
X
x
X
p
3
m
3}
m
o
»
<
O
u
R
m
<•
m
3
m
I
6
-------
Ash Fusion Temperature
Some coals tend to clinker, slag and foul the boiler more than others.
This is because the ash from these coals becomes sticky and begins to melt
at lower temperatures. These coals have low ash fusion temperatures. Clinkering,
slagging and fouling will decrease boiler efficiency by reducing the amount of
heat absorbed by the boiler and increasing the stack gas heat loss. Firing a
coal with a lower ash fusion temperature than that for which the boiler was de-
signed can also lead to reduced boiler capacity, and it may require operation
of the boiler at a higher and less efficient excess air level.
Free Swelling Index (FSI)
The free swelling index provides an indication of the caking
characteristics of coal when burned on fuel beds. The caking characteristic
of coal is the tendency of coal to melt together into a solid mass when rapidly
heated. The free swelling index (FSI) is reported on a scale of 1 to 9 in
increments of 1/2. Coals having a FSI from 1 to 3 are generally referred to
as "free burning", from 3i to 5 as moderately caking, and from 5i to 9 as
strongly caking. Caking characteristics have little or no effect on the per-
formance of spreader stokers. However, free burning and moderately caking
coals are preferred for overfeed stokers and underfeed stokers.
KVB4-15900-560
55
-------
SUMMARY
The information presented in this document is meant to inform the
operator of the various factors affecting coal stoker fired boiler emissions
and efficiency over which he has control. It is meant to supplement his own
experiences and the guidance provided by the boiler-stoker manufacturers *
It is hoped that this information will stimulate those in charge of
coal stoker fired boilers to review their own maintenance and operating
practices and to strive for improvements in their unit's efficiency and emis-
sions. Remember that reducing the excess air alone can often save enough
money to cover the operators salary. And, with the continued rise in fuel
prices, the potential savings are growing larger each year.
If the reader is interested in more detailed information on the re-
sults of the American Boiler Manufacturers Association's extensive stoker
test program, he may refer to the reports described in references 1 through 12.
A final technical report summarizing the data from all of the above reports
will be published by the U.S. Environmental Protection Agency soon after this
document is released. The title of the final technical report will be "Emissions
and Efficiency Performance of Industrial Coal Stoker Fired Boilers."
KVB4-15900-560
56
-------
REFERENCES
1. Gabrielson, J. E., P. L. Langsjoen, and T. C. Kosvic. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site A. EPA-600/7-78-136a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, July, 1978. 106 pp..
2. Gabrielson, J E., P. L. Langsjoen, and T. C. Kosvic. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site B. EPA-600/7-79-041a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, February, 1979. 113 pp.
3. Gabrielson, J. E., P. L. Langsjoen, and T. C. Kosvic. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site C. EPA-600/7-79-130a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, May, 1979. 138 pp.
4. Gabrielson, J. E., P. L. Langsjoen, and T. C. Kosvic. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site D. EPA-600/7-79-237a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, November, 1979. 115 pp.
5. Langsjoen, P. L., J. O. Burlingame, and J. E. Gabrielson. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site E. EPA-600/7-80-064a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, March, 1980. 102 pp.
6. Langsjoen, P. L. R. J. Tidona, and J. E. Gabrielson. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site F. EPA-600/7-80-065a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, March, 1980. 113 pp.
7. Langsjoen, P. L., J. O. Burlingame, and J. E. Gabrielson. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site G. EPA-600/7-80-082a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, April, 1980. 114 pp.
8. Langsjoen, P. L., R. J. Tidona, and J. E. Gabrielson. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site H. EPA-600/7-80-112a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, May, 1980. 90 pp.
9. Langsjoen, P. L., J. O. Burlingame, and J. E. Gabrielson. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site I. EPA-600/7-80-136a. U.S. Environmental Protection
Agency, Research Triangle Park, NC, May, 1980. 77 pp.
10. Langsjoen, P. L., J. O. Burlingame, and J. E. Gabrielson. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site J. EPA-600/7-80-137a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, May, 1980. 83 pp.
KVB4-15900-560
57
-------
11. Langsjoen, P. L., J. O. Burlingame, and J. E. Gabrielson. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site K. EPA-600/7-80-138a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, May, 1980. 96 pp.
12. Davis, J. W., and H. K. Owens. Field Tests of Industrial Stoker Coal-Fired
Boilers for Emissions Control and Efficiency Improvement - Sites Ll - L7.
EPA-600/7-81-020a, U.S. Environmental Protection Agency, Research Triangle
Park, NC, February, 1981. 65 pp.
13. Babcock & Wilcox Company. Steam - Its Generation and Use. 37th Edition.
New York, N.Y., 1960. Section 16.
14. Babcock & Wilcox Company. Steam - Its Generation and Use. 38th Edition.
New York, N.Y., 1972. Sections 6 and 11.
15. Marks' Standard Handbook for Mechanical Engineers, Eighth Edition. McGraw
Hill Book Company, New York, N.Y., 1978. pp. 7-6.
16. American Society of Mechanical Engineers, Steam Generating Units. Power
Test Code 4.1 - 1964, Reaffirmed 1973. pp. 16, 17, 67.
KVB4-15900-560
58
-------
BIBLIOGRAPHY
Coal Burning Equipment. Based on the publication by: Smith, W. S. , and
Gruber, C. W. Atmospheric Emissions from Coal Combustion - An Inventory
Guide. Public Health Service Publication No. 999-AP-24, April, 1966.
Coal Combustion, Power from Coal Part II A Special Report. Power,
March, 1974.
Dick, J. L., Spreader Stokers. In: Proceedings of the Industrial Coal
Conference, University of Kentucky, Lexington, Kentucky. April, 1965.
Hollander, H. I., Another Look at the Traveling Grate Stoker. In: Pro-
ceedings of the Industrial Coal Conference, University of Kentucky, Lexington,
Kentucky. April, 1965.
Johnson, H. E., Underfeed Stokers. In: Proceedings of the Industrial Coal
Conference, University of Kentucky, Lexington, Kentucky. April, 1965.
Langsjoen, P. L., Boiler Tune-Up. In: Proceedings of the Energy Efficient
Equipment Conference, Illinois State University, Normal, Illinois, 1979.
Tieman, J. W., A Review of Coal Characteristics and Analysis. In: Pro-
ceedings of the Industrial Coal Conference, University of Kentucky, Lexington,
Kentucky. May 2-3, 1979.
Wood, S. C., and Langsjoen, P. L., State of Missouri Boiler and Combustion
Efficiency Manual. October, 1978.
KVB4-15900-560
59
-------
APPENDIX A
CONVERSION FACTORS
ENGLISH AND METRIC UNITS TO SI UNITS
To Convert From
To
Multiply By
in
in2
ft
ft2
ft3
Ib
Ib/hr
lb/106Btu
g/Mcal
Btu
Btu/lb
Btu/hr
J/sec
J/hr
Btu/ft/hr
Btu/ft/hr
Btu/ft2/hr
Btu/ft2/hr
Btu/ft3/hr
Btu/ft3/hr
psia
"H20
Rankine
Fahrenheit
Celsius
Rankine
APPROXIMATE CONVERSION
ppm @ 3% O2 (SOx as SO2)
ppm @ 3% O2 (NOx as NO2)
ppm @ 3% 02 (CO)
ppm @ 3% O2 (CH4)
g/Kg of Fuel
cm
cm2
m
m2
m3
Kg
Mg/s
ng/J
ng/J
J
J/kg
W
W
W
W/m
J/hr/m
W/m2
J/hr/m2
W/m3
J/hr/m3
Pa
Pa
Celsius
Celsius
Kelvin
Kelvin
FACTORS FOR A TYPICAL
ng/J (lb/106Btu)
ng/J (Ib/lO^Btu)
ng/J (lb/106Btu)
ng/J (lb/!06Btu)
ng/J (lb/106Btu)
2 = 540
60 452
0.3048
0.09290
0.02832
0.4536
0.1260
430
239
1054
2324
0.2929
1.000
3600
0.9609
3459
3.152
11349
10.34
37234
6895
249.1
C = 5/9R-273
C = 5/9(F-32)
K = C+273
K = 5/9R
COAL FUEL
0.851 (1.98xlO~3)
0.611 (1.42xlO~3)
0.372 (8.65xlO-4)
A
0.213 (4.95xlO~4)
4300 (10)
KVB4-15900-560
60
-------
APPENDIX B
CONVERSION FACTORS
SI UNITS TO ENGLISH AND METRIC UNITS
To Convert From
To
cm
cm2
m
m2
m3
Kg
Mg/s
ng/J
ng/J
J
J/kg
J/hr/m
J/hr/m2
J/hr/m3
W
W
W/m
W/m2
W/m3
Pa
Pa
Kelvin
Celsius
Fahrenheit
Kelvin
APPROXIMATE CONVERSION
ng/J
• ng/J
ng/J
ng/J
ng/J
in
in2
ft
ft2
ft3
Ib
Ib/hr
lb/106Btu
g/Mcal
Btu
Btu/lb
Btu/ft/hr
Btu/ft2/hr
Btu/ft3/hr
Btu/hr
J/hr
Btu/ft/hr
Btu/ft2/hr
Btu/ft3/hr
psia
"H2°
Fahrenheit
Fahrenheit
Rankine
Rankine
FACTORS FOR A TYPICAL COAL FUEL
ppm @ 3% O2 (SOx as
ppm @ 3% O2 (NOx as
ppm @ 3% O2 (CO)
ppm @ 3% 02 (CH4)
g/kg of fuel
so2)
N02)
Multiply By
0.3937
0.1550
3.281
10.764
35.315
2.205
7.937
0.00233
0.00418
0.000948
0.000430
0.000289
0.0000881
0.0000269
3.414
0.000278
1.041
0.317
0.0967
0.000145
0.004014
F
F
R
R
1.8K-460
1.8C+32
F+460
1.8K
1.18
1.64
2.69
4.69
0.000233
KVB4-15900-560
61
-------
APPENDIX C
SI PREFIXES
Multiplication
Factor
10
18
12
10
10
103
-
10 -
io-2
10-3
10"6
10-9
10-12
10
-18
Prefix
exa
peta
tera
giga
mega
kilo
hecto*
deka*
deci*
centi*
mi Hi
micro
nano
pi co
femto
atto
SI Symbol
E
P
T
G
M
k
h
da
d
c
m
U
n
P
f
a
*Not recommended but occasionally used
KVB4-15900-560
62
-------
APPENDIX D
EMISSION UNITS CONVERSION FACTORS
FOR TYPICAL COAL FUEL (HV = 13,320 BTU/LB)
Multiply
To Vv-\ By
Obtain
% Height in Fuel
S N
lbs/106Btu
S02 N02
grams/106Cal
S02 N02
PPM
(Dry @ 3% 02)
SOx NOx
Grains/SCF.
{Dry @ 12* CO2)
S02 N02
% Weight
In Fuel
0.666
0.370
0.405
13.2X10"4
0.225
1.48
5.76X10"4
.903
lbs/106Btu
SO,
1.50
NO,
(.556)
19.8xlO~4
(2.23)
2.47
(.556)
14.2X10"4
(2.23)
SO,
2.70
grams/106Cal
(1.8)
NO,
4.44
35.6xlO~4
(4.01)
(1.8)
25.6x10"
(4.01)
SOx
758
PPM
505
281
(Dry @ 3» 02)
NOx
1736
704
1127
391
1566
Grains/SCF
SO,
.676
(.448)
(.249)
8.87x10
-4
(Dry @12% C02)
N02
1.11
(.448)
(.249)
6.39x10"
NOTE: 1. Values in parenthesis can be used for all flue gas constituents such as oxides of carbon,
oxides of nitrogen, oxides of sulfur, hydrocarbons, particulates, etc.
2. Standard reference temperature of 530°R was used.
KVB4-15900-560
63
-------
APPENDIX E
SUMMARY SHEET
A.SME TEST FORM
FOR ABBREVIATED EFFICIENCY TEST
PTC 4.1-a(1964)
TEST NO. BOILER NO.
DATE
OWNER OF PLANT LOCATION
TEST CONDUCTED BY OBJECTIVE OF TEST
DURATION
BOILER MAKE 4 TYPE RATED CAPACITY
STOKER TYPE & SIZE
PULVERIZER, TYPE & SIZE BURNER, TYPE
FUEL USED MINE COUNTY STATE
& SIZE
SIZE AS FIRED
PRESSURES & TEMPERATURES FUEL DATA
]
2
3
4
5
6
7
8
9
10
II
15
13
U
STEAM PRESSURE IN BOILER DRUM
STEAM PRESSURE AT S. H. OUTLET
STEAM PRESSURE AT R. H. INLET
STEAM PRESSURE AT R. H. OUTLET
STEAM TEMPERATURE AT S. H. OUTLET
STEAM TEMPERATURE AT R H INLET
STEAM TEMPERATURE AT R.H. OUTLET
WATER TEMP ENTERING (ECON ) (BOILER)
STEAM QUALITY!". MOISTURE OR P. P.M.
AIR TEMP. AROUND BOILER (AMBIENT)
TEMP AIR FOR COMBUSTION
(This is Reference Temoerolure) T
TEMPERATURE OF FUEL
GAS TEMP. LEAVING (Boiler) (Econ.) (Air Hlr.)
GAS TEMP. ENTERING AH (II conditions to be
corrected to auorantee)
PSlrt
PStcr
plio
psio
F
F
F
F
F
F
F
F
F
UNIT 0 UANTITIES
15
16
17
18
19
JO
21
22
23
24
25
ENTHALPY OF SAT. LIQUID (TOTAL HEAT)
ENTHALPY OF (SATURATED) (SUPERHEATED)
STM.
ENTHALPY OF SAT. FEED TO (BOILER)
(ECON.)
ENTHALPY OF REHEATED STEAM R.H. INLET
ENTHALPY OF REHEATED STEAM R. H.
OUTLET
HEAT AB5/LB OF STEAM (ITEM 16 -ITEM 17)
HEAT ABS/LB R.H. STEAM(ITEM 19-ITEM 18)
DRY REFUSE (ASH PIT * FLY ASH) PER LB
AS FIRED FUEL
Btu PER LB IN REFUSE (WEIGHTED AVERAGE)
CARBON BURNED PER LB AS FIRED FUEL
DRY GAS PER LB AS FIRED FUEL BURNED
Btu/lb
Btu/lb
Btu/lb
Btu/lb
Btu/lb
Btu'Ib
Btu/lb
Ib/lb
Btu/lb
Ib/lb
Ib/lb
HOURLY OUAKTITIES
26
27
29
29
30
31
ACTUAL WATER EVAPORATED
REHEAT STEAM FLOW
RATE OF FUEL FIRING (AS FIRED wt)
TOTM, "F^T INPIIT ('""" 2a x "em 4"
1000
HEAT OUTPUT IN SLOW-DOWN WATER
J|J*L(l'em26.llem20)»(ltem27»llem21)tltem30
OUTPUT 1000
Ib/hr
Ib/hr
Ib/hr
kB/hr
IrB/hf
kB/hr
FLUE OAS ANAL. (BOILERMECON) (AIR HTR) OUTLET
32
33
34
35
36
CO,
0,
CO
Nj (BY DIFFERENCE)
EXCESS AIR
% VOL
% VOL
". VOL
% VOL
".
COAL AS FIRED
PROX. ANALYSIS
37
33
39
40
MOISTURE
VOL MATTER
FIXED CARBON
ASH
TOTAL
41
42
Btu per Ib AS FIRED
ASH SOFT TEMP.1
ASTM METHOD
% wt
COAL OR OIL AS FIREO
ULTIMATE ANALYSIS
43
44
45
46
47
40
37
CARBON
HYDROGEN
OXYGEN
NITROGEN
SULPHUR
ASH
MOISTURE
TOTAL
COAL PULVERIZATION
48
49
50
64
GRINDABILITY
INDEX'
FINENESS JJTHRU
50 M-
FINENESS % THRU
200 M-
INPUT-OUTPUT
EFFICIENCY OF UNIT S
51
52
•i?
44
41
OIL
FLASH
Sp. Gray
POINT F'
ity Deg. API*
VISCOSITY AT SSU-
BURNER SSF
TOTAL HYDROGEN
% wt
Btu per Ib
GAS
•54
55
5n
57
58
59
60
61
CO
CH4 METHANE
C,H, ACETYLENE
C,H. ETHYLENE
CjH, ETHANE
H,S
CO,
H,
HYDROGEN
TOTAL
62
63
41
TOTAL HYDROGEN
% wt
SVOL
DENSITY 68 F
ATM. PRESS.
Btu PER CU FT
Btu PER LB
ITEM 31
100
ITEM 29
HEAT LOSS EFFICIENCY
"5
66
67
63
69
70
71
75
HEAT LOSS DUE TO DRY GAS
HEAT LOSS DUE TO MOISTURE IN FUEL
HEAT LOSS DUE TO H,O FROM COMB.OFH,
HEAT LOSS DUE TO COMBUST. IN REFUSE
HEAT LOSS DUE TO RADIATION
UNMEASURED LOSSES
Btu/lb
A. F. FUEL
TOTAL
EFFICIENCY = (100 - Item 71)
% o( A. F.
FUEL
'Not Required for Efficiency Testing
t For Point of Measurement See Par. 7.5.8.1-PTC 4.1-1964
KVB4-15900-560
64
-------
CALCULATION SHEET
APPENDIX F
ASME TEST FORM
FOR ABBREVIATED EFFICIENCY TEST
PTC 4.1-b (1964)
Revised September, 1965
OWNER OF PLANT TEST NO. BOILER NO. DATE
30
24
25
36
65
66
67
68
69
70
71
72
' ITEM IS ITEM 17"
iobb
If impractical to weigh refuse, this
item can be estimated as follows
DrvRcru-crcnLBorA-riRCDrucL- » *SH 'N AS FIRED COAL HOTE- IF FI
" 100 - % COMB. IN REFUSE SAMPLE p,T RE(rUSE
r- — IN COMBUST
ITEM 43 pTEM22 ITEM 23 | SHOULD BE
CARBON BURNED x SEPARATEL1
PER LB AS FIRED = — - ; = COMPUTATIC
FUEL 10° L 100° J
DRY GAS PER LB 11CO, * 80, t 7(N, * CO)
BURNED" 3(c°> * co) ' '"/ \" ' r
ITEM32 ITEM 33 • [ ITEM 35 ITEM 34 ) ITEM 24
11 X + 8 x * 7 \ * /x
/ITEM 32 ITEM 34 \ |_
3 v 1 * /
\ I
CO ITEM 34
.2682N, - (O. - co 1 ITFU It
' ~Z~ 7687 (ITFM 1!) (ITFM IS ..'.„)
* 2
HEAT LOSS EFFICIENCY
HEAT LOSS DUE LB DRY GAS ITEM 25 (ITEM 13) -(ITEM 11)
TO DRY GAS * PER LB AS xC X ('Ivg - 'oir) = X0.24 =
FIRED FUEL * Unit ....
HEAT LOSS DUE TO . LB H,0 PER LB r (ENTHALPY OF VAPOR AT 1 PSIA & T GAS LVG)
MOISTURE IN FUEL 'AS FIRED FUELX KENTHALPY OF
• (ENTHALPY OF LIQUIDAT T AIR)] - ... x[(FNTHALPY OF VAPOR
100
AT 1 PSIA i. T ITEM 13) -(ENTHALPY OF LIQUID AT T ITEM 11)1 =
HEAT LOSS DUE TO H,0 FROM COMB. OF H, = 9H, x [(ENTHALPY OF VAPOR AT 1 PSIA & T GAS
LVG) - (ENTHALPY OF LIQUID AT T AIR)]
= 9 X ITEM " X [(ENTHALPY OF VAPOR AT 1 PSIA & T ITEM 13) - (ENTHALPY OF LIQUID AT
100 T ITEM 11)] *
HEAT LOSS DUE TO ITEM 22 ITEM 23
COMBUSTIBLE IN REFUSE * x =
HEAT LOSS DUE TO TOTAL BTU RADIATION LOSS PER HR
RADIATION* LB AS FIRED FUEL — ITEM 28
UNMEASURED LOSSES **
TOTAL
EFFICIENCY * (100 - ITEM 71)
kB/hr
UE DUST & ASH
DIFFER MATERIALLY
BLE CONTENT, THEY
ESTIMATED
'. SEE SECTION 7,
)NS.
+ 3 s)
ITEM 47
267 J
Btu/lb
AS FIRED
FUEL
LOSS x
100 '
41
li X 100 *
41
67
X100 =
41
68
»» oir ... Aopondi. 9.2 - PTC 4.1-1964
* If losiei are not m.oiur.d, ui. ABMA Standard Rodiation Lost Chort, Fig. t. PTC 4.1-1964
•• Unm.oiur.d loss*! listed in PTC 4.1 but not tabulated above may by provided for by assigning O mutually
agreed upon value for Item 70.
KVB4-15900-560
65
-------
APPENDIX G
ABMA STANDARD RADIATION LOSS CHART
CM
CT)
20.
.75
.87 .
420
1,1 ...
i .4
t
' \ >--•>;
'•°||fpw
2 ^
^ *
10,^-,-.
;t ,!...._ . ..
.0,--,--..
~ ~ t t Water Wa
.y 1114 H II j
o Use Facto
ijc : :: Air Coole
.6 ji
•*?4
2 , - .
/
* ,
, '
• Walls
iplliiii
^ X s . TV^
k ^ ^ N AW?
S \ / '* S N
- *||r - '^"ST
Is Only ^
r Below for
J Walls E:::
V
s
_
^
The Radiation L
for o Differential
~ Temperatures or
Over the Surlac<
h
fr
• s -
s
'•s
s
-S,
fc-
_
s
s
s
i^
t
S
X
s
s
^
^ _ -
\
i:5":
S
»
^
^
vvi=!
• !i4 j^
^
s
x
^
S
s
is
S
3
A
P
B
A
E
~ *
^f
«,,-
!
FURNACE WALL MUST HAVE AT LEAST ONE THIRD ITS
ROJECTED SURFACE COVERED BY WATER COOLED SURFACE
EFORE REDUCTION IN RADIATION LOSS IS PERMITTED
IR THRU COOLED WALLS MUST BE USED FOR COMBUSTION
r REDUCTION IN RADIATION LOSS IS TO BE MADE
XAMPLE: UNIT GUAR.FOR MAX. CONT. OUTPUT OF 400
MILLION BTU/HR WITH THREE WATER COOLED
WALLS.
LOSS AT 400 = 0.33% LOSS AT ZOO = 0.68%
f0<1
I s
1
y
~ tj
iss Values Obtained From This Curve are
of 50 F Between Surface and Ambient
o-
\
-
.-i
d for an Air Velocity of IOO Feel per Minute
. Any Correction for Other Conditions should
rdance with Fig. 3 Page 170 in Ihe 1957
V
Manual of ASTM Standards on Refractory Materials
Illlllll ! 1
II II Illlllll Illl
V
.
s
S
_
^*
_
-
T5""
\
***:
Fffr
4-
; S
PrX1
• T
I rv
i >
r —
R
N
V
s
s
^
^
l~i-
ADU
4-V;C
-
V
h
S,
S
S
i"
kTION
'<&--
\
\\
4-
*t
V
i
_s
"T"1
LOSS
s
s
v
A
rrl
"11
y
S
' s
T MAX.
"...
... | _| +T
:::! u_:B
T t j
"
:::±1,
= = -|^
wi^
^v '
\
\l
=
-
JONT. OUTPUT.
tt 1
TT f
-
llf | _|_
•"•^ / V\H 3 4 5 6 7 8 9 10 2O 30 40 SO 6O 80 100 20O 300 4OO 6OO BOO KXO 20OO 4OOO 6OOO lOpOO 20pOO
81 .83 .94 10
90 .93 .97 I.O
Want Walt Factor
Air Coolad Walt Factor
ACTUAL OUTPUT MILLION BTU PER HOUR
KVB4-15900-560
-------
TECHNICAL REPORT DATA
(Please reed Inunctions on the reverse before completing}
1. REPORT NO.
EPA-600/8-81-016
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
A Guide to Clean and Efficient Operation of Coal-
Stoker-Fired Boilers
S. REPORT DATE
Mav 1981
I. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
, PERFORMING ORGANIZATION REPORT NO.
P. L. Langsjoen
9. PERFORMING ORGANIZATION NAME AND ADDRESS
KVB, Inc.
6176 Olson Memorial Highway
Minneapolis, Minnesota 55422
10. PROGRAM ELEMENT NO.
C9BN1B
11. CONTRACT/GRANT NO.
IAG-D7-E681 (EPA);
EF-77-C-01-2609 (DOE)
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development*
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
ERIOO COVERED
13. TYPE OF REPORT AND PERIOD COVI
User Manual; 6/77-12/80
14. SPONSORING AGENCY CODE
EPA/600/13
is. SUPPLEMENTARY NOTES ffiRL-RTP project officer is R.
DOE project officer is W.T.Harvey Jr. (*) ABMA
E. Hall, MD-65, 919/541-2477.
and DOE are cosponsors.
i6. ABSTRACT
report is a guide for those in charge of operating coal-stoker-fired
boilers. It explains and illustrates the types of coal-fired stokers in operation today.
It explains the combustion process in simple terms. It explains the various heat
losses in stoker boilers. And, it discusses ways in which coal-stoker-fired boilers
may be operated at peak efficiency and with minimum pollutant emissions. Included
are step-by-step instructions for optimizing excess air levels. The guidelines are
based on the findings of an extensive coal-stoker test program cofunded by the
American Boiler Manufacturers Association (ABMA), the U.S. Department of
Energy, and the U.S. Environmental Protection Agency.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Pollution
Boilers
Stokers
Coal
Improvement
Efficiency
Flue Gases
Fly Ash
Combustion
Instructions
Air Pollution Control
Stationary Sources
Particulates
Operating Guidelines
Spreader Stokers
Overfeed Stokers
Underfeed Stokers
13B
13A
2 ID
14G
21B
13. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report I
Unclassified
21. NO. OF PAGES
72
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (»-73)
67
------- |