CD A '-'-^- Environmental Protection Agency Industrial Environmental Research
•• • •« Office of Res'\ii'jh iintl Development Laboratory
Research Triangle Park, North Carolina 27711
EPA-600/7-76~029
EMISSIONS FROM RESIDENTIAL
AND SMALL COMMERCIAL STOKER
COAL-FIRED BOILERS UNDER
SMOKELESS OPERATION
Interagency
Energy-Environment
Research and Development
Program Report
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RESEARCH REPORTING,SERIES
Research reports of the Office of Research and Development, U.S.
Environmental Protection Agency, have been grouped .into seven series.
These seven broad categories were established to facilitate further
development and application of environmental technology. Elimination
of traditional grouping was consciously planned to foster technology
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1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
,5. Socioecpnomic Environmental Studies
. 6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from
the effort funded under the 17-agehcy Federal Energy/Environment
Research and Development Program. These studies relate to EPA's
mission to protect the public health and welfare from adverse effects
of pollutants associated with energy systems. The goal of the Program
is to assure the rapid development of domestic energy supplies in an
environmentally—compatible manner by providing the necessary
environmental data and control technology. Investigations include
analyses of the transport of energy-related pollutants and their health
and ecological effects; assessments of, and development of, control
technologies for energy systems; and integrated assessments of a wide
range of energy-related environmental issues.
REVIEW NOTICE
This report has been reviewed by the participating Federal
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signify that the contents necessarily reflect the views and
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This document is available to the public through the National Technical
Information Service, Springfield-, Virginia 22161.
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EPA-600/7-76-029
October 1976
EMISSIONS FROM
RESIDENTIAL AND SMALL COMMERCIAL
STOKER-COAL-FIRED BOILERS
UNDER SMOKELESS OPERATION
by
Robert D. Giammar, Richard B. Engdahl, and Richard E. Barrett
Batte lie-Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
Contract No. 68-02-1848
Program Element No. EHE624
EPA Project Officer: John H. Wasser
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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ABSTRACT
The reported research assessed the advisability of increased
utilization of stoker coal for residential and small commercial space
heating applications. The assessment was based on (1) an experimental
laboratory study (major emphasis) to evaluate the emissions from a 20-hp
(200 kW) boiler firing anthracite, Western subbituminous, processed lignite
char ("smokeless coal") and high- and low-volatile bituminous coals.
Pollutants of major interest were smoke, particulate, and POM; (2) a.
survey to identify the manufacturers and designs of stokers currently
marketed, and (3) a_ survey to identify processes for manufacturing smoke-
less coals and to evaluate their suitability for stoker firing.
The results of the experimental study indicate that smokeless
operation of a small stoker could be achieved for the coals evaluated.
The coals generating the highest smoke levels also generated the highest
particulate and POM levels. Coals with the highest volatile matter and
the highest free swelling index had the highest levels of these emissions.
The experiments indicate a potential for reducing emissions by minor
modifications in the design and operation of the stoker and by utilizing
processed or treated coals. Even these reduced emission levels would be
considerably higher than those from- equivalent oil- and gas-fired system.
The results of the stoker and smokeless coal surveys suggest that
there is insufficient demand for small .stokers to justify the needed R&D
to refine stoker designs and commercialize smokeless coal processes.
Current economic and environmental factors associated with
stoker firing are unfavorable for increased coal usage in residential
and small commercial applications. Although our supplies of fuel oil and
natural gas are dwindling, there appears to be no immediate or near term
shortage for most small users. Where shortages exist, alternative
methods of space heating (such as electric space heating coupled with
extensive insulation) will be selected rather than stoker firing.
111
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CONTENTS
Abstract iii
Figures v
Tables v
Acknowledgment vi
1. Introduction 1
2. Overall Program Objectives and Scope 2
3. Summary of Results 3
4. Assessment of the Results 6
5. Recommendations for Future Work 6
6. Background on Stoker Design and Operation 7
7. Plan of Experimental Investigation 13
Experimental facility 13
Coal selection and acquisition 15
Experimental runs and operating conditions 18
Experimental procedures 19
8. Experimental Results 22
Coal combustion on the fuel bed 38
Factors influencing emission levels 39
Overview of experimental results 43
9. Assessment of the Potential for Stoker Coal Utilization ... 44
Appendices
A. Survey of stoker-boiler manufacturers 48
B. Smokeless coal survey 57
References 76
IV
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FIGURES
Number Page
1 Conventional stoker assembly 8
2 Typical record of C02 content of flue gases from a small
stoker operating under intermittent control 10
3 Typical plot of retort and stack temperature during cyclic
operation (10-minutes on and 50-minutes off) 11
4 Stoker fed boiler facility 14
5 Stack-gas temperature as a function of time indicating the
four discrete time periods for sampling 21
TABLES
1 Coal Analysis 17
2 Summary of Experimental Data 23
3 Emission Factors for the Five Stoker Coals 25
4 POM Analysis 26
5 The Effect of Volatile Matter and Free Swelling Index on
Particulate and POM Emissions from Coal Combustion During
a 20-Minute On/40-Minute Off Cycle and Continuous Firing
Rates of 45 to 67 Ib/hr 40
6 Emission Factors for Fossil Fuel Combustion 51
7 Automatic Heating Trends 52
8 Estimate of Boiler Population for Small Commercial Units ... 54
9 Stokers 55
10 Boilers 55
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ACKNOWLEDGMENT
The research covered in this report was pursuant to Contract No.
68-0-1848 with the U.S. Environmental Protection Agency, Combustion Research
Section. The authors acknowledge the assistance of EPA Project Officers
J. W. Wasser and W. S. Lanier who participated in planning this program
and have provided helpful comments. The authors also thank other Battelle-
Columbus staff who have contributed to this study—R. Coleman, P. W. Jones,
H. G. Leonard, T. C. Lyons, R. E. Poling, and P. E. Strup.
VI
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SECTION 1
INTRODUCTION
Coal was still a major fuel fired in residential and small com-
mercial heating systems as late as the 1950's. Coal usage then rapidly
declined as the market areas of the less expensive, more conveniently
utilized, and more environmentally acceptable fuels (gas and oil) expanded.
Even in certain geographical locations where coal was cheaper than oil or
gas, the high maintenance costs and labor associated with firing coal,
coupled with an increased desire for a clean environment, virtually
eliminated the use of coal for residential and small commercial space heat-
ing applications by the 1960's.
The emissions from residential and small commercial stokers were
never extensively characterized (by today's standards) as the sophisticated
instrumentation currently used was not available. However, visible smoke
was easily measured and stokers were notorious for their cyclic smoke
emissions. Attempts to alleviate this problem included refinement of stoker
designs and development of manufacturing processes to convert high volatile
coals to a "smokeless" coal. Before these designs and processes received
widespread application (and further development), the stoker market dis-
appeared. As a consequence, after only a relatively short period of
research and development, advancement of the technology of stoker firing
was halted.
Today, the uncertainty in both the short- and long-term avail-
ability of oil and gas has renewed an interest in burning coal to meet our
nation's energy needs. To assist EPA in making a technical assessment of
the environmental impact of burning coal, specifically in residential and
small commercial applications, Battelle-Columbus conducted a program to
evaluate the emissions from residential and small commercial coal-fired
stokers. (Small commercial was defined as equipment with less than one
million Btu/hr input.)
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SECTION 2
OVERALL PROGRAM OBJECTIVES AND SCOPE
The overall objectives of this program were (1) to evaluate
emissions from residential and small commercial stoker-fired boilers under
typical boiler operation, including smokeless operation, and (2) to assess
the advisability of increased utilization of coal for these applications,
including consideration of operating efficiency, fuel type and availability,
economics, emissions, and public acceptance. This program consisted of:
1. A survey to identify the manufacturers and designs of
stokers currently being marketed
2. A survey to identify processes for the manufacturing
of smokeless coals and to evaluate the suitability of these
fuels for stoker firing
3. An experimental laboratory study to measure emissions
while firing a stoker-fired boiler system with five
candidate fuels. For this study, a 20-hp (200 kW)
stoker was fired with anthracite, Western subbituminous,
processed lignite char ("smokeless coal"), and high-
and low- volatile bitumnious coals. Pollutants of
interest included NO, S02, CO, smoke, particulate, and
polycyclic compounds.
The major emphasis of the body of this report is focused on the experimental
laboratory program; the survey of stoker manufacturers and the survey of
smokeless coal processes are discussed in Appendices A and B, respectively.
Pertinent information from these surveys has been incorporated in the
Summary and the assessment of the potential utilization of coal for small
commercial stoker applications.
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SECTION 3
SUMMARY OF RESULTS
The results of the experimental research investigation, the stoker
manufacturer survey, and the "smokeless" coal survey can be summarized as
follows.
Experimental Research Investigation
The results of the experimental research investigation are as
follows:
• Smokeless operation of a small stoker was achieved
for the coals evaluated.
• In general, coals that generated the higher smoke
levels also generated the higher particulate and
POM emission levels.
• Coals with the highest volatile matter content
and the highest free-swelling index had the
highest levels of particulate and POM emissions.
• Anthracite (a naturally smokeless coal) was the
only coal investigated that could be burned with
a uniform flame. This coal generated the lowest
smoke, particulate, and POM emissions.
• The processed smokeless coal was effective in
achieving low smoke and POM emissions. However,
this coal was soft and broke into an excessive
amount of fines when fired, thus producing an
unexpectedly high particulate loading; It is
anticipated that this problem can be overcome
by utilizing a suitable binder.
• Significant reduction in particulate and POM
emissions were achieved for the high volatile
bituminous coal with minor modifications in the
design and operation of the stoker. These same
modifications were ineffective in reducing
emissions from the Western subbituminous coals.
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• POM emissions generated from steady-state firing
of the stoker were significantly higher than those
generated from steady-state operation of oil-fired
equipment. In addition, compared to oil combustion,
a greater percentage of the POM compounds generated
from stoker coal firing are considered to be
potentially carcinogenic.
• Higher particulate loadings were generated during the
"off" cycle than during the "on" for the coals having
volatile matter contents greater than 20 percent.
Stoker Survey
After surveying over twenty present or past manufacturers (or their
representatives) of residential and small commercial stoker-fired space heat-
ing equipment, it was concluded that:
• Stoker technology has not advanced in the past 25
years as the declining market could not justify
stoker R&D.
• There has been renewed interest in stoker firing in
the size ranges of interest. The majority of interest
has been for small commercial applications rather than
for residential installations.
• Where gas and oil are not available, residential
space heating is accomplished by electric heat
resistance heating rather than stoker firing.
• Residential and small commercial stoker-boilers are
similar in design as system components are scaled
(up or down) to match the desired range of
operation. The stokers are of the underfeed type.
• The conventional underfeed anthracite stokers are
designed to fire anthracite only. Because anthracite
burns to an easily handled powderlike ash, some
underfeed anthracite stoker designs include auto-
mated ash removal.
• Only one manufacturer of the conventional bituminous
stoker in the size range of interest could be identi-
fied. This manufacturer sells about 500 units/yr
in the U.S., mainly as replacement units. These
stokers are generally installed in rural communities.
• Only one manufacturer of the conventional anthracite
stoker in the size ranges of interest could be
identified. This manufacturer sells only a few
units per year.
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o The majority of new stoker-boiler systems are
designed for hot water, while most replacements are
for steam systems. There has been some renewed
interest in stoker-fired warm-air furnaces, but no
significant amount of sales.
• The cost of the stoker itself is a significant
portion (almost half) of the overall cost of the
stoker-boiler system. Gas and oil burners in this
size range are significantly less expensive than
stokers.
Smokeless Coal Survey
The findings from the survey of processed smokeless fuels include:
1. There is currently no significant market for
processed "smokeless" stoker fuels.
2. There are currently no commercially available
processed "smokeless" coals suitable for stoker
firing. Only one smokeless fuel plant operating
on a commercial scale in the United States was
identified. This plant markets a briquet suitable
for hand firing.
3. The technology exists to manufacture a processed
smokeless coal suitable for stoker firing.
4. The brief survey of environmental impact of
smokeless coal process plants suggests that
process emissions can be controlled with
current emission control technology.
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SECTION 4
ASSESSMENT OF THE RESULTS
Several factors can be defined that would enhance the market posi-
tion of small stokers, as follows:
• An increased concern over the continued availability
(and price) of natural gas and fuel oil
• Further stoker development: the experimental investi-
gation suggests that stoker firing can become more
environmentally acceptable through changes in design
and operation of the stoker
• Availability of suitable stoker fuels: it appears
that a process coal can be manufactured that would
enhance the acceptability of stoker firing.
However, in spite of these factors, the current economic and environmental
considerations, along with the inconvenience associated with coal firing,
make widespread stoker use unattractive.
SECTION 5
RECOMMENDATIONS FOR FUTURE WORK
It is recommended that future research on small stokers be focused
on making stoker firing a more acceptable and competitive method of space
heating by (1) determining the necessary practical modifications in the
design and operation of stokers to reduce emissions and eliminate operating
problems (cakings, etc.), and (2) identifying and evaluating suitable processed
or treated coals. The minor modifications in the stoker design and operation
considered in this program showed promise and other (major) modifications
should be investigated. Recently developed processed or treated low-sulfur
coals, such as those developed by TRW (Meyer's Process) and Battelle-
Columbus (hydrothermally treated) should also be considered for stoker
firing. In addition, a processed coal with a limestone binder (similar to
those used in Korea during the 1950*s) offers promise for S02 control.
Furthermore, in any future work, it is recommended that additional pollution
measurements and corresponding analyses (as in EPA's Level I/Level 2
Methodology) be conducted to provide a complete characterization and
evaluation of coal types and system modifications.
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SECTION 6
BACKGROUND ON STOKER DESIGN AND OPERATION
Smoke evolved when burning high-volatile coal has always been a
problem for residential and small commercial heating units. Development of
the residential underfeed stokers, such as the inverted-underfeed stoker
designed by Battelle in the 1940's, made it possible to burn high-volatile
coal smokelessly. However, recent attention has focused on all emissions,
which includes not only smoke but NOX, SOX, CO, CO, particulate, and POM.
Levels of the individual emissions are related to stoker design, stoker
operation and firing procedure, and/or the type of coal burned. These
aspects are discussed below.
Stoker Design
The small mechanical stokers in the range of interest are of the
underfeed type with a worm-feed mechanism. This type of stoker is used for
firing coal at rates up to about 1200 Ib/hr (550 Kg/hr). In contrast to
hand firing or spreader stokers, underfeed stokers supply fresh coal to the
boiler or furnace by feeding it underneath the hot coals. The underfeed stoker
consists of a retort, blower, air duct, air duct control, feed screw, motor
and transmission. Figure 1 is an illustration of a typical stoker assembly.
Retort—
The retort is a cast-iron chamber in the shape of a cup or trough in
which the coal is devolatized and ignited. The retort is surrounded by a
windbox and contains slotted holes for admitting air under slight pressure
to the fire. These slotted holes, or air admitting ports, are often referred
to as the tuyeres.
Feed Screw—
The feed screw conveys the coal from the hopper to the retort, or with
a bin-fed type, directly from the coal bin to the retort. The feed screw
extends from the coal supply (hopper or bin) through the coal-feed tube into
the retort, where it discharges the coal it conveys.
Blower and Air Control—
Blowers for supplying combustion air in the underfeed stokers are
usually squirrel-cage types that provide relatively high pressures and low
volumes. The blower is equipped with either a manual or automatic damper
to regulate air flow. The blower develops sufficient static pressure to
overcome a series of resistance generated by flow through the regulating
damper, air duct, tuyeres, and fuel bed.
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FIGURE 1. Conventional stoker assembly.
Side illustration showing
various parts:
1. Hopper
2. Electric motor
3. Transmission
4. Coal feed tube
5. Feed worm
6. Retort
7. Clean out opening
8. Retort air chamber.
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Motor and Transmission—
The coal-feed screw is driven by an electrical motor, usually mounted
on top of the transmission. The motor drives the transmission through V-belts.
Operation of the motor is controlled by various electrical devices including
room thermostat, boiler limit switch, and the hold-fire timing relay. The
transmission rotates the coal-feed screw; the rotational speed of the feed
screw is determined by the capacity of the heating system. Feed rates can be
varied by changing either the screw ratchet setting or transmission pulleys.
Stoker Operation
The residential and small commercial stoker-boilers operate basically
the same in principle although their operating cycles can be different depend-
ing upon application. Characterization of the operation of these units is
complicated because they seldom operate with a steady-state heat-release rate.
Off-On Cycle-
Small stokers operate in an off-on cycle. When "on" (feed screw operating)
the stoker always feeds coal at a constant rate, it adjusts to varying loads
by varying the percent "on" time in each cycle. During the "on" time, fresh
coal is fed underneath the hot coals and air is admitted through the tuyeres.
The heat-released rate increases substantially as the fuel bed temperatures
gradually increase. Fuel bed temperatures often do not reach a steady-state
temperature before the thermostat stops the stoker screw and fan. Upon shut-
down the fuel bed continues to burn, but the heat-release rate is reduced
drastically as the bed is being supplied by minimal quantities of air by the
natural draft. At this time unburned hydrocarbons can be released because
of insufficient air. Figure 2, a plot of C02 levels as a function of time,
illustrates the nonsteady heat-release rate of stokers (1).* Figure 3 shows
a typical plot of retort and stack temperatures during continued cyclic opera-
tion of a stoker on a 10-minute on and 50-minute off cycle (2).
Full-Load and Hold-Fire Operating Cycles—There are two extremes in
stoker-boiler operation, namely, full-load and no-load. During full-load
operation, the stoker is running continuously; however, the stoker is
stopped for at least 5 minutes in every 30-minute cycle so that bed tempera-
tures cool and the ash fuses. (The "off" time can vary with ash content
composition of the fuel. Anthracite with a low ash content and high fusion
temperature can be burned continuously with no "off" period.) If not given
an opportunity to cool, the ash may remain fluid and sticky forming agglo-
merated massive clinkers with resulting nonuniform feeding and irregular
burning.
During the no-load period, the boiler operates in a "hold-fire" mode
of operation. In the hold-fire mode, the stoker is fired for short periods
to keep the fuel bed sufficiently alive to respond quickly when the boiler
load increases, otherwise the fuel bed temperature will be too low to ignite
fuel that enters the retort during the next on-period. The typical hold-
fire period for bituminous coal is approximately a 5-minute operation of the
stoker in each 30 minutes. (The hold-fire period for anthracite can be as
low as one minute every half hour.) Partial load operation falls in between
these extremes.
* References are listed on page 76.
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20
16
_ 12
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Time
c
p
l_
0)
Jf
o
V)
0
.*
O
00
6
o
oo
SOmln
o
co
o
oo
Retort temperature
lOmln
200
300
400 500
Temperature, F
600
700
FIGURE 3. Typical plot of retort and stack temperature during
cyclic operation (10-minutes-on and 50-minutes off).
11
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Coal Selection
Selection of stoker coals is of paramount importance in successful
stoker operation. (In today's environmentally aware society, successful
stoker operation is generally equated to proper operation of the stoker without
visible smoke emissions.) Proper stoker adjustments for smokeless operations
are largely dependent on the coal analysis and coal size. For instance,
unsatisfactory stoker operation (high smoke) occurs if
• A large percentage of fines either restricts the amount
of air that reaches the fuel bed, or the fines are
carried off the fuel bed and out of the stack.
• A high percentage of ash results in troublesome clinker
formation.
• A low ash-fusion point coal creates clinkers that are
difficult to remove from the stoker because the ash
melts and fuses or sticks to the tuyeres.
Accordingly, the most desirable coals for small stoker operation
are relatively free-burning, low-volatile, low-ash and low-sulfur coals
that are sized 3/4 x 1/4 inches (1.9 x 6.4 mm). The free-burning coals
include all coals that do not cake. (Caking coals emit tars and swell when
heated.) These coals burn to a fine ash and do not restrict air flow through
the fuel bed. Low volatile coals tend to burn slowly with a uniform flame
and as a consequence do not generate appreciable levels of smoke over the
entire stoker operating cycle. Finally, sulfur oxide emission levels are
related to the sulfur content of the fuel, and, thus, the low sulfur coals
are the most desirable from the environmental viewpoint.
12
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SECTION 7
PLAN OF EXPERIMENTAL INVESTIGATION
Five candidate stoker coals were evaluated in a 20-hp (200 kW)
commercial boiler. The majority of research was conducted at one boiler
operating cycle and at a moderate boiler load of about 22 percent of rated
full-load capacity. [Operating load is determined by two factors: firing
rate during the "on" time and percent "on" time. Thus, a unit rated at 75
Ib/hr (34 kg/hr) but fired at 50 Ib/hr (22 kg/hr) for a 20-minute-on/40-
minute-off cycle would operate at a load of 22 percent (50/75 x 20/60 x 100).]
A limited number of experimental runs were conducted at other boiler cycles
and boiler loads. Emissions of primary interest were smoke, particulate,
and POM while those of secondary interest included SOo, CO, and NO.
EXPERIMENTAL FACILITY
Overall System
Figure 4 is a photograph of the overall system layout that was used
for the stoker research. This system includes:
• Kewanee 3R-5, 20-bhp (200 kW) , fire-tube, hot-water boiler
• Will-Burt 75 Ib/hr (34 kg/hr) bituminous stoker
• 14-in. (0.35 m) diameter stack section
• Sampling platform.
\
A Van Wert 60 Ib/hr (27 kg/hr) anthracite stoker (not shown) was also used
to fire the boiler for selected runs. These two stokers were selected as
they were the only commercially available stokers in the size range of
interest.
Approximately 10 pipe diameters above the boiler stack-gas outlet,
4 sampling ports were installed. These ports were utilized to sample during
discrete time periods of stoker-boiler operation. Approximately 5 feet (1.5m)
above the sampling ports a damper was installed to provide a control of the
draft at the boiler outlet. Ports for smoke and gaseous-emission sampling
and for temperature and pressure measurements were provided at the base of
the stack.
13
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Figure 4. Stoker-fed boiler facility
14
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Stokers
Bituminous Stoker—
The Will-Burt 75 Ib/hr (34 kg/hr) stoker is a conventional bituminous
underfeed stoker. The majority of coal is burned in the retort with the re-
maining coal being burned on a ceramic hearth surrounding the retort. In
srokers of this size, there is no provision for automatic removal of ash.
The Will-Burt stoker is supplied with a 3-groove pulley that is
used to control the coal feed rate. The coal feed screw and blower are
driven with the same motor. Air flow rate is controlled by a damper on the
blower inlet. During the checkout of the facility, it was observed that the
blower did not have sufficient capacity, even at the lower firing rates.
As a consequence, the blower was removed and the laboratory compressed air
line was used to supply the combustion air. The air flow rate was measured
with a standard ASME orifice.
Over-fire air jets are not normally included as part of the stoker-
boiler furnace. However, 4 air jets [6 in. (0.15 m) on center] 0.28 in.
(7 mm) in diameter were installed approximately 12 in. (0.31 m) above the
retort. The overfire or secondary air flow rate, approximately 10 to 15
percent of the underfeed or primary air flow rate, was measured with a
rotameter.
Anthracite Stoker—
The Van Wert stoker is a conventional anthracite underfeed stoker.
This particular design did not include provision to vary the coal feed rate.
Combustion air was supplied by a fan that was directly coupled to the stoker
motor. Air flow could be modulated by a damper on the fan inlet. With this
stoker, the anthracite was completely burned within the retort and the ash
would fall to a pit below the retort. This dry, powderlike ash would not
interfere with the combustion or air distribution.
COAL SELECTION AND ACQUISITION
Coals were selected to provide a range of fuels representative of
residential and small commercial stoker utilization.
Basis for Selection
Because of the vast number of candidate stoker fuels, guidelines
compatible with the overall objectives of this program were established to
restrict the number of potential coals. These guidelines included:
• Geographical source of each fuel should represent
a substantial availability for residential and
commercial use of the representative type.
• The processed smokeless fuel should be obtained from
a commercially operated process.
1-5
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• Natural smokeless coals should be selected for comparison
with the processed fuel.
e Coals of dissimilar characteristics should be selected
to represent fuels not considered smokeless.
• Shipping distance should be chosen to minimize
transportation costs.
• All fuels should be obtained in a size suitable for
stoker firing.
Accordingly, the following five coals were identified and procured in
approximately 1.5 ton (1.5 metric ton) quantities.
Processed Smokeless Fuel—
Lignite char briquettes were procured from Husky Industries of
Dickenson, North Dakota. These briquettes required crushing and double
screening [1 x 1/4 in. (25 x 6.4)] as they were pillow-shaped, similar to
a charcoal briquette. A corn flour binder had been used that appeared to
be unsuitable for stoker firing. During the crushing and screening, it
was observed that the coal was soft and crumbled easily. Only 40 percent
of the original briquette remained in the desired size range after screen-
ing.
Anthracite—
Because of its low volatile content, anthracite was considered as
a natural smokeless fuel. An experimental lot of Number 1 Buckwheat
[9/16 x 5/16 in. (14 x 7.9 mm)] Pennsylvania anthracite was procured
through Blue Coal Corporation of Wilkes-Barre, Pennsylvania.
Low-Volatile Bituminous—
This coal is also considered a natural smokeless coal because of
its relatively low volatile content for a bituminous coal. A quantity of
stoker [1 x 3/8 in (25 x 9.5 mm)] Pochantas Seam 3 coal from the Bishop
Mine, in Bishop, West Virginia was procured.
High-Volatile Bituminous—
The high-volatile bituminous coal procured was an Elkhorn Number 3
Seam coal from the Poly Mine at Irvine, Kentucky. The coal size was about
1-1/4 x 1/4 in. (32 x 6.4 mm).
Western Subbituminous—
This coal was mined from the Black Diamond Seam of the Corely strip
mine in Fremont County, Colorado. This stoker coal was air-cleaned and
sized to 1-1/4 x 5/8 in (32 x 16 mm).
Fuel Analysis—
Table 1 lists properties of the coals that were fired during this
program. The analyses are reported on an "as received" basis and include
the moisture content of the coals. This moisture content can vary randomly
from day to day, depending on climatic condition, and is also dependent
16
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TABLE 1. COAL ANALYSIS
Proximate Analysis, percent v.-\t>monrai Ar,ai,rc-!Q PV«O Moan™
Fixed
Coal Carbon
High volatile
bituminous 53.5
Low volatile 70.8
bituminous
Western sub- 45.4
bituminous
Processed lignite 61.6
char
Anthracite 71.5
Volatile percent Swelling Value ,.,,
Matter Ash Moisture CHS Index*-3-* Btu/tt>
40 4.7 1.8 79.5 5.7 1.2 5 14,100
21.4 6.9 0.9 84.7 4.7 0.6 7.5 14,700
37.4 9.2 8.0 64.6 4.2 0.6 0.5 11,400
16 15.1 7.3 67.9 1.7 0.6 0 10,600
3.9 12.3 12.3 79.4 2.0 0.7 0 11,900
(a) A high value is indicative of a highly caking coal.
(b) 1 Btu/lb = 2326 J/Kg.
-------
upon washing procedures used at the mine. In general, however, the moisture
content gives a measure of the inherent moisture content of the coal. The
free-swelling index is a measure of the caking properties of the coal, as
indicated by high values of the caking bituminous coals.
EXPERIMENTAL RUNS AND OPERATING CONDITIONS
Gaseous and Smoke Characterization Runs
Initially, each coal was characterized by making gaseous and smoke
emission measurements as a function of excess air for several firing rates
and boiler operating cycles to determine the range of smokeless operation.
Smokeless operation was defined as no visible smoke in the stack gas as
determined by visual observation. Once these conditions were established,
the boiler stack was probed to generate transient temperature and velocity
profiles to establish appropriate sampling rates for particulate and POM
sampling.
Evaluation Runs
As can be seen from Figure 2, for most coals, a stoker operating
under intermittent operation seldom burns with any uniform and repeatable
pattern — the result of a continuously changing fuel bed. Accordingly,
to provide some measure of control of the fuel bed, when making emission
measurements, before emission sampling was begun, the stoker was operated
sufficiently long to establish a stable fuel bed, but not so long that ash
buildup and/or clinker formation would significantly interfere with the
performance of the stoker. Thus, emission measurements were made at com-
parable, but relatively optimum, stoker firing conditions, rather than at
conditions representative of practical or typical operation.
Firing Rates
Although the stoker-boiler system was designed for a 75 Ib/hr
(34 kg/hr) firing rate, at this firing rate, the coal flames (except
anthracite) would impinge upon the boiler crown sheet causing quenching of
the flame and smoke formation. As a consequence, firing rates were reduced
to about 45 to 55 Ib/hr (20 to kg/hr), except for anthracite that could be
successfully fired at 67 Ib/hr (30 kg/hr). In addition, it was necessary
to fire with overfire air for the high- and low-volatile bituminous coals
as well as for the Western subbituminous coal to achieve smokeless operation.
For anthracite and the process smokeless coal, both lower in volatile
matter, overfire air was not required to achieve smokeless operation.
For the high-volatile bituminous and Western subbituminous coals,
firing at rates of about 23 and 75 Ib/hr (10 to 34 kg/hr) during the "on"
time were also investigated. (Residential and small commercial designs
generally include provision to adjust the feed rate for about one-third,
two-third, and full load.)
18
-------
Boiler Operating Cycles
In an investigation of emissions from small commercial oil- and
gas-fired furnaces (3), an operating factor of 1/3 (10-minutes-on/20-
minutes-off cycle) was considered as typical. Accordingly, for comparison
purposes, several cycles which would provide a 1/3 operating factor were
considered. It was observed that when operating the boiler on a 10-minutes-
on/20-minutes-off cycle, the fuel bed began to degrade after a few cycles.
The degradation was attributed to incomplete combustion of raw coal rather
than ash buildup or clinker formation. This was especially noticeable for
the low-volatile bituminous coal. Increasing the length of the cycle from
30 minutes to 60 minutes alleviated this problem. Therefore, a 20-minutes-
on/40-minutes-off cycle was selected as the basic cycle to evaluate the
emissions from the firing of each coal.
The high-volatile bituminous and Western subbituminous coals were
also .fired on a 50-minute-on/10-minute-off cycle.
EXPERIMENTAL PROCEDURES
Particulate and POM Sampling Procedure
The operating cycle of a stoker-boiler creates a unique problem
in obtaining meaningful particulate and POM emissions data. As discussed
earlier, the stoker seldom operates at a steady-state condition. Transients
occur not only during the starting and stopping of the stoker but throughout
each "on" and "off" period of operation. In addition, and most importantly,
during the "off" period, the fuel bed continues to burn as a small amount
of air is supplied by the natural draft of the stoker-boiler system. Accord-
ingly, the stack flow was characterized to determine transient temperature
and velocity profiles throughout the 60-minute cycle. From an integration
of these profiles, an appropriate probe position (within the stack) and
sampling rate was determined for each period of stoker operation.
Stack Probing—
Hot-wire anemometry was used to characterize stack flow as a func-
tion of time as conventional sampling apparatus instrumentation did not
have adequate sensitivity or response time. Two hot-wire probes (quartz-
coated hot-film sensors with instantaneous response time) were used
simultaneously. Probe 1 was located approximately 2 ft below the sampling
port and contained a hot-wire sensor set stationary on the centerline to
monitor axial flow velocity with time. In addition, a thermocouple was
attached to monitor temperature with time. These data were used as a base-
line measurement. Probe 2 was used to determine the velocity profile
across the duct at the sampling position.
Sampling Period and Rate Determination—
The transient stack-probe data were analyzed to relate the tempera-
ture and velocity profiles to stoker-cycle operation. Because these profiles
were essentially flat across the 14-in. (0.36 m) diameter stack, sampling was
simplified as traversing was not necessary.
19
-------
Figure 5 is a plot of stack-gas temperature versus time during
one 20-minutes-on/40-minutes-off cycle while firing the high-volatile
bituminous coal. The stack-gas velocity curve is similar in shape. As
shown in Figure 5, the cycle is divided into 4 discrete time periods. These
time periods were selected as representative of discrete periods of stoker
operation, namely: (1) transient on, or startup, (2) "steady-state" on,
(3) transient off or shutdown, and (4) "steady-state" off. The period of
each of these discrete time segments was based not only on the time-rate-of-
change of stack-gas velocities and temperatures, but also upon the smoke
densities within each segment. Generally, during time periods (1) and (3),
startup and shutdown, respectively, smoke is visible from the stack for a
few minutes, indicating at least a different quality (if not quantity) of
the emissions. Accordingly, a separate sampling train was used for sampling
during each time segment to provide a relative measure of particulate and
POM emission levels for each time segment within the cycle. Furthermore,
use of four sampling trains permitted a more accurate approach to isokinetic
sampling than could be achieved with one or two trains.
Because temperature and velocity were rapidly changing within some
segments of the cycle (especially during startup and shutdown), it was deter-
mined that the sampling rate could not be continually adjusted to provide
true isokinetic sampling. Therefore, hot-wire anemometer measurements
(both velocity and temperature) were integrated over each time segment to
determine an average velocity and temperature and, thus, an average sampling
rate for each segment. The nozzle of each train was pointed upstream only
when a sample was being drawn; otherwise, they were rotated 180° so that
they pointed downstream. To obtain a representative sample, measurements
were made over 4 to 6 cycles. This required that each probe be rotated 8 to
12 times during a run. During the later runs of the program, only two trains
were used, one for the "on" period and the other for the "off" period.
Analytical Procedures
Particulate and POM levels were determined by a modified EPA Method 5
procedure with the probe wash and filter catch being used to determine the
filterable particulate loadings and an adsorbent column being used to deter-
mine POM loadings (4).
Gaseous emissions were determined by: paramagnetic analysis for
oxygen; flame ionization detection for unburned hydrocarbons; nondispersive
infrared for carbon monoxide, carbon dioxide, and nitrogen oxide; and a
dry electrochemical analyzer for sulfur dioxide. Smoke emissions were deter-
mined with a Bacharach smoke tester according to the ASTM filter-paper
method for smoke measurements (5). Although it is realized that this method
of smoke determination was developed for distillate oil-fired systems and not
coal-fired systems, it provided a quick, convenient determination of the
relative levels of smoke.
Feed-Rate Determination
The coal feed rate for each stoker was determined by weighing the
amount of coal that was required to refill the stoker hopper after the stoker
was operated for some specific time period. This procedure determined an
average coal feed rate and not an average burning rate.
20
-------
500
400
0>
o
300
200
100
I I
I I I I
10 15 20
25 30 35
Time, minutes
40 45 50 55 60
FIGURE 5. Stack-gas temperature as a function of time indicating
the four discrete time periods for sampling.
21
-------
SECTION 8
EXPERIMENTAL RESULTS
The performance of the stoker and the emissions that it generates
are dependent upon a number of factors that include the properties of the
coal and combustion operating parameters. Coal properties can be defined
in reasonably precise terms using ASTM procedures. Conversely, while
there are some measurements to characterize combustion conditions (e.g.,
CC>2 and 02 in the flue gas, coal firing rate, etc.), there are few
measurements to characterize the fuel bed other than visual observations
and/or photographs. Hence, these qualitative observations are necessary
to provide a description of the fuel-bed combustion. Accordingly, in
addition to experimental measurements tabulated in Tables 2, 3, and 4,
visual observations of fuel bed conditions are included in the interpre-
tation of the data.
Table 2 summarizes the stoker operating conditions and the gaseous,
smoke, particulate, and POM emissions generated during the firing of the
five different stoker coals for the conditions listed. Because stoker com-
bustion conditions are rarely a true steady state, the gaseous emission
levels shown during Time Segments 1 and 2 indicate the range of these
emissions during the on-period of operation, while those shown in Time
Segments 3 and 4 indicate the range during the off-period. Because it was
observed during the early runs that the particulate and POM emissions were
not appreciably different between Time Segments 1 and 2 and also between
3 and 4, only two trains, one for the "on" period (Time Segments 1 and 2)
and the other for the "off" period (Time Segments 3 and 4) were used during
the later runs.
22
-------
TABLE 2. SUMMARY OF EXPERIMENTAL DATA
Run
1
2
3
4
5
6
7
8
9
10
11
12
Cjcle, <•»
on/off 1°'*-
Coal . - min. percent
Blgh-volatlle 20/40 19
bituminous
High-volatile 20/40 20
bltumlnoua
High-volatile 50/10 '9
bltumlnoua
Processed 20/40 20
Western 20/40 24
Low-volatile 20/40 23
bituminous
Western 20/40 23
High-volatile 20/40 19
bituminous
Anthracite 20/40 30
Anthracite 50/10 74
Western 20/40 lo
High-volatile 20/40 33
bituminous
(b) .
Firing Air Floe Bal
Rate, .Prim.- Sec
Ib/hr Ib/hr Ib/h,
42
0
44
0
44
0
45
0
55
0
52
0
52
0
43o
67
0
S7
o -
23
0
75
0
500
0
500
0
500
0
450
0
640
0
610
0
660
0
50g
fan
0
fen
0
350
0
760
0
50
0'
SO
0
50
0
0
0
60
0
60
0
53
0
50o
0
0
0
0
o
0
75
0
>.. •
r oercent
476-"
11.6
• 13:9
15.8
5.4-
8.5
17.0-
18.5
5.0-
6.5
10.5-
12.8
8.0-
12.5
17.0-
18.5
10.5-
12.3
18.1"
18.5
5.5
12.0
11.0
15.8
10.7-
12.4
15-18
7-10
12-15
10-
12.6
16-
17
7-10
13-15
12.5-15.5
14.5-18:3
4-6
14-15
Gas .Analvala
C02.
percent
-8-5.~-
14.6
4.6-
6.0
11.6-
14.3
2.4
3.6
15.2-
16.5
8.0"
9.8
8.6-
11.0
2.4-
3.6
8.1-
9.8
2.4-
2.6
8.0
16.0
4.6
9.0
8.4-
10
1.8-2.2
9.4-11
4.1-6.7
8.4-
10-
3.3-
3.7
9.6-12.5
6-8
2.0r7.0
1.9-3.0
13-13.8
4.2-5.6
S02,
ODffl
~ 600--
800
360-
420
510-
750
150-
180
630-
900
500-
580
170
30-
40
210-
270
30-
40
..
--
—
--
._
-
"
200-240
60-100
240-280
130:150
120-180
50-100:
..
---
HO,
pom
160---
200
55-
60
200-
240
30-
40
600-900
60-
100
120
20
30
120
130
< 40
120
170
30-
50
_.
-
"--
30-40
10-
15
60-90
30-40.
80-100
10T30
200-250
'40-70"
CO.
pom
165-
>1250
>1250
60-
100
>1250
40-
100
>1250
100-
>1250
>1250
560-
850
>1250
<60
>1250
«!-
80
>1250
40-160
>1250
150- 1
> 80
>1250
>1250
tin"
640
>1250
POM
Bacharach Time
Smoke Segment
- 5-
>9
>9
6-
^•9
>9
7-
>9
4-5
1-
2
2-4
>9
3-4
7-
'>«
4-6
>9
--
1/2
1/2
1/2
1/2
0
0
150->1250 6->9
>1250
40-80
>1250
>9
4-W
>9
1
2"
3
4
1
2
3
4
1
2
3
1
2
3
4
,
2
3
4
1
2
3
4
1&2
36A
1&2
3&4
1
2
3
4
1
2
3
1&2
36A
1&2
3&4
Samollni
Length
o£_Time
'Segment L
Min:
5
15 -
6
34
-•5
15
6
34
7
43
10
6
14
8
32
6
12
10
30
7
13
8
32
20
40
20
40
5
15
10
30
5
35
10
20
40
20
40
i
Ho. of
, Segmen
Sample
6
6
6
l(c>
4
7
7
l(c)
3
6
6
6
6
6
6
6
6
6
5
6
6
6
3
6
6
6
6
5
5
5
5
6
6
6
5
6
5
5
Partlculate
Results
ts Total,
d tntt
34.7
116.6
700.3
248.6
40.6
218.4
910.4
198.5
119.6
367.7
760.7
217.2
623.4
42.3
12.5
38.9
58.5
42.2
285.5
120.7
174.9
298.1
231.1
73.72
313.8
189.1
394.2
26.8
73.8
23.7
13.5
63.5
617.9
53.5
76.9
194.9
233
1838
Loadlna
110
110
1400
2400
160
200
1600
810
110
100
1300
290
390
44
4
66
43
52
110
180
120
390
190
37
99
590(d)
84
70
26
5.3
160
160
54
45
61
120
610
POM Reai.
ilts
Total. Loading
4.6
7.1-
4.5
3.0
2.5
9.3
12.8
4.2
8.6
6.7
16.5
0.24
0.17
0.09
0.19
0.87
1.5
1.3
3.5
0.39
1.8
16.7
7.8
„
--
-
0.112
0.157
0.0200
0.0301
0.0565
0.325
0.107
0.92
0.69
1.6
1.0
13;9
6.5
9.0
28.7
9.8
8.2
23.0
17.2
7.6
1.8
28.7
0.33
0.11
0.09
0.66
1.5
1.1
1.6
1.5
0.57
1.1
22
6.4
._
-
-
0.35
0.15
0.022
0.012
0.14
0.008
0.11
0.53
0.22
0.81
0.33
-------
TABLE 2. (Continued)
KJ
PCM Sampling
13
14
IS
16
17
High-volatile
High-volatile
on/off
20/40
20/40
20/40
(e)
20/40
(e)
20/40
Load,
percent
10
11
33
22
20
Firing
Rate ,
Ib/hr
23
0
25
0
75
0
50
0
45
0
Prlmj_
Ib/hr
350
0
400
0
880
0
600
0
550
0
Sec
Ib/hr
40
0
40
0
85
0
60
100
60
100
percent
10-13
15-17
12-14
16-18
5-7
14-18
9.5-12.8
15.5-18.2
9.5-11
15T17.5
Gaa Analysis
C02,
6.5-7.9
3.5-4.5
6.3-9.0
2-4
13.4-14.8
2-5
7.1-10-2
1.9-5.2
7.6-9.6
2.6-3.8
S02,
ppm
-.
--
--
280-500
80-100
190-240
40-90
-
NO,
pom
120-170
40-70
100-130
40-60
150-190
25-50
100-140
40-9
220-280
50-80
CO,
ppm
>1250
>1250
100-140
>1250
20-40
>1250
50-150
>1250
100-200
>1250
Bacharach
Smoke
>9
>9
5-9
>9
4-6
>9
3-5
6->9
8-9
Time
Senment
1&2
3&4
1&2
3&4
142
36A
16,2
3&4
1&2
3M
Length
Segment,
rain.
20
40
20
40
20
40
25
35
25
35
Partlculate
No of
Segments
Sampled
5
5
5
5
--
5
5
4
3
Results
Total,
ma
232
600
86.7
31.7
1396
651
93.5
300
165
517
Loading..
130
190
50
94
77
160
37
87
93
290
Total, Loading,
0.46
0.57
0.76
0.56
0.41
2.5
2.5
2.0
3.0
3.3
0.26
0.18
0.44
0.17
0.23
0.60
0.98
0.58
1.7
1.9
(a) Load Is given In percentof continuous rated-load operation.
(b) Lb/hr = .454 Kg/hr.
(c) Partial segment.
(d) Broken frit.
(e) Modified cycle: During the first 5 minutes of the "on" cycle, the primary air flow was only 200 Ib/hr. In addition, during the flrat 5 mlnutee
of the "off" cycle, the secondary (overflre air Jets) remained on to help reduce smoke.
-------
TABLE 3. EMISSION FACTORS FOR THE FIVE STOKER COALS
\
/ "\\/
Bacharach
Run Coal
1 High-volatile bituminous
2 ditto
8
17
12
13
3
5 Western subbituminous
7 ditto
16
15
11
14
6 Low-volatile bituminous
4 Processed lignite char
9 Anthracite
10 Anthracite
Cycle, Fi
on/off, R
min. lb
ring Smoke
ate On-
/hr^ Cvcle
20/40 42 5->9
20/40 44 6->9
20/40
20/40 (b)
20/40
20/40
50/10
20/40
20/40
20/40(b)
20/40
20/40
20/40
20/40
20/40
20/40
50/10
43 6->9
45 8-9
75 4->9
23 »
44 7->9
55 2-4
52 4-6
50 3-5
75 4-6
23 6->9
25 5-9
52 3-4
45 4-5
67 0.5
67 0
rarticulate
Loading
On-
Off- Cycle,
Cvcle me/Nm3
>9
>9
>9
>9
>9
>9
>9
>9
>9
6->9
>9
>9
>9
7->9
1
0.5
0.5
110
190
110
93
120
130
100
50
37
37
77
45
50
140
360
73
160
Off-
Cycle^
m?/N'mJ
1600
1400
590(8)
290
610
190
1300
99
99
87
160
61
94
260
13
11
54
POM
On-
L/n
Cycle
mg/Nm3
8.2
8.8
--
1.7
.81
.26
3.2
1.2
--
0.98
0.23
0.53
0.44
1.0
0.17
0.12
0.21
Loading
r\f c
UI I
Cycle
mg/ Mm3
13
21
--
1.9
.33
.18
29
1.5
--
0.58
0.60
0.22
0.17
12
0.68
0.15
0.11
Particulate
Emissions ,
g/lb
coal fed
3.9
4.1
--
1.7
2.1
3.4
0.85
0.50
0.43
0.60
1.0
1.0
0.77
1.4
3.2
0.33
0.70
POM
Emiss ions ,
mg/lb
coal fed
86
82
—
12.3
8.8
5.4
23
10.2
--
11.1
3.4
8.3
7.3
27
1.8
0.86
0.12
— -- --
(a) Broken frit.
(b) Modified.
-------
TABLE 4. POM ANALYSIS
NJ
HAS
Component Notation
Anthracene/Phenanthrene •/-x""'
Methyl anthracenes \^^
Fluoranthene \/^
Pyrene
Methyl Pyrene/Fluoranthene-^"^
Benzo(c)phenanthrene '• ***
Chrysene/Benz(a)anthracene *
Methyl chrysenes *
7, 12-Diciethylbenz (a) anthracene ****
Benzo f luoranchenes **
Benz(a and e)pyrenes ***
Perylene
3-Methylcholanthrene ****
Indeno(l,2,3,-cd)pyrene *
Benzo (ghi) per ylene
Dibenzo(a,h)anthracene ***
Dibenzo(c,g)carbazole ***
Diber.z(ai and ah)pyrenes ***
POM
POM Loading
Time Segment: 1
mg
1.30
0.74
0.53
0.41
0.64
0.041
0.023
0.14
—
0.19
0.13
—
0.081
0.043
0.029
0.071
—
0.018
4.6
mg/Nm
3.9
2.2
1.6
1.2
1.9
0.1
0.07
0.4
—
0.6
0.4
—
0.2
0.1
0.09
0.2
—
0.05
13.9
mg
2.44
1.04
1.43
0.92
0.34
0.071
0.36
0.10
—
0.24
0.12
—
—
0.034
0.030
—
—
—
7.1
Run No.
2
mg/Nm
2.2
1.0
1.3
0.8
0.3
0.06
0.3
0.09
—
0.2
0.1
—
0.03
0.03
—
—
—
—
6.5
1
mg
0.63
0.29
0.85
0.53
0.25
0.024
0.27
—
—
0.99
0.65
—
—
—
—
—
—
—
4.5
3
mg/Nm
1.3
0.6
1.7
1.1
0.5
0.05
0.5
—
—
2.0
1.3
—
—
—
—
—
—
—
9.0
mg
0.57
0.43
0.33
0.23
0.68
0.40
0.28
0.090
—
0.16
0.10
—
0.07
0.015
0.010
—
—
—
3.0
4
mg/Nm
5.5
4.1
3.2
2.2
6.5
0.4
2.7
0.9
—
1.5
1.0
—
0.7
0.1
0.01
—
—
—
28.7
TABLE 4. (Continued)
-------
N3
Run No. 2
WAS
Component dotation
Anthracene/Phenanthrdne
Methyl anthracenes
Fluoranthene
Pyrene
Methyl Pyrene/Fluoranthene
Benzo(c)phenanthrene ***
Chrysene/Benz(a)anthracene *
Methyl chrysenes *
7, 12-Dimethylbenz (a) anthracene ****
Benzo f luoranthenes **
Banz(a and e)pyrenes ***
Perylene
3-Methylcholanthrene ****
Indeno(l,2,3,-cd)pyrene *
Benzo (ghi)perylene
Dibenzo(a,h)anthracene ***
Dibenzo(c,g)carbazole ***
Dibenz(ai and ah)pyrenes ***
POM
POM Loading
Time Segment: 1
mg
1.02
0.53
0.24
0.18
0.17
0.01
0.080
0.04
—
0.070
0.055
—
0.045
0.020
0.015
~
—
•~™
2.4
mg/Nm
4.0
2.1
0.9
0.7
0.7
0.04
0.3
0.2
—
0.3
0.2
—
0.2
0.08
0.06
— "
— —
™~
9.8
2
mg
4.22
1.54
1.41
0.96
0.32
0.065
0.33
0.065
—
0.019
0.090
—
0.005
0.060
0.015
~
~ —
_ —
9.3
mg/Nm
3.7
1.4
1.2
0.8
0.3
0.06
0.3
0.06
—
0.02
0.08
—
0.05
0.05
0.013
—
— —
~~
8.2
3
mg
2.94
0.098
1.19
0.88
0.94
0.17
0.89
0.44
—
1.79
1.30
—
0.64
0.26
0.41
~—
~~
~*~
12.8
mg/Nm
5.3
0.2
2.0
1.6
1.7
0.3
1.6
0.8
—
3.2
2.3
— —
1.2
0.5
0.7
__,
~"~
~~
23.0
4
mg
1.03
0.57
0.32
0.22
0.25
0.030
0.24
0.29
—
0.35
0.31
—
0.40
0.13
0.095
~™
~~
*™
4.2
mg/Nm
4.2
2.3
1.-3
0.9
1.0
0.1
1.0
1.2
— —
1.4
1.3
—
1.6
0.5
0.4
~~
~~
"™
17.2
TABLE 4. (Continued)
-------
OC
Run No. 3
KAS
Component Notation
Anthracene/Phenanthrene
Methyl anthracenes
Fluoranthene
Pyrene
Methyl Pyrene/Fluoranthene
Benzo(c)phenanthrene ***
Chrysene/Benz(a)anthracene *
Methyl chrysenes *
7,12-Dimethylbenz(a)anthracene ****
Benzo f luoranthenes **
Benz(a and e)pyrenes ***
Perylene
3-Methylcholanthrene ****
Indeno(l,2,3,-cd)pyrene *
Benzo (glii)perylene
Dibenzo(a,h)anthracene ***
Diber.zo(c,g)carbazole ***
Dibenz(ai and ah)pyrenes ***
POM
POM Loading
Time Segment: 1
mg
1.58
1.06
2.00
1.20
1.37
0.018
0.013
0.64
—
0.38
0.26
—
0.16
0.13
0.07
0.24
—
0.08
8.7
mg/Nm
1.4
0.9
1.7
1.0 .
1.2
0.02
0.01
0.06
—
0.3
0.2
—
0.1
0.1
0.06
0.2
—
0.07
7.6
2
mg
2.25
1.12
1.62
0.99
0.014
0.10
0.28
0.082
—
0.14
0.061
-'-
0.033
0.007
0.009
—
—
—
6.7
mg/Nm
0.6
0.3
0.4
0.3
0.004
0.03
0.08
0.02
—
0.04
0.02
—
0.009
0.002
0.002
—
—
—
1.8
Qg
1.58
1.08
1.60
0.90
1.00
0.11
1.00
0.62
—
2.50
2.21
—
1.53
1.20
1.22
—
—
1.08
16.5
3 4
3 3
mg/Nm mg mg/Nm
2.7
1.9
2.8
1.6
1.7
0.2
1.7
1.1
—
4.3
3.8
—
2.7
2.1
2.1
—
.
1.9
28.7
TABLE 4. (Continued)
-------
WAS
Component Notation
Anthracene/Phenanthrene
Methyl anthracenes
Fluoranthene x
Pyrene <— -""
Methyl Pyrene/Fluoranthene
Benzo(c)phenanthrene ***
Chrysene/Benz(a)anthracene ~^ *
Methyl chrysenes *
7, 12-Dimethylbenz (a) anthracene ****
Benzo f luoranthenes **
Benz(a and e)pyrenes ***
Perylene
3-Methylcholanthrene ****
Indeno(l,2,3,-cd)pyrene *
Benzo (ghi ) perylene
Dibenzo (a, h) anthracene ***
Dibenzo(c,g)carbazole ***
Dibenz(ai and ah)pyrenes ***
POM
POM Loading
Time Segment : 1
mg
0.035
0.020
0.035
0.030
0.020
0.005
0.040
0.020
—
0.015
0.010
— —
0.005
0.005
0.003
—
—
— —
0.24
/« 3
mg/Nm
0.05
0.03
0.05
0.04
0.03
0.007
0.06
0.03
—
0.02
0.01
—
0.007
0.007-
0.004
—
—
— —
0.33
Run No.
2
mg
0.010
--0.020
-0.035
•JO'. 030
0.005
0.015
0.010
0.005
—
0.010
0.010
—
0.005
0.010
0.003
—
—
—
0.17
mg/Nm
0.006
0.01
0.02
0.02
0.003
0.01
0.006
0.003
—
0.006
0.006
—
0.003
0.006
0.002
—
—
—
0.11
4
3
mg
-0.017
-O'.Oll
JX011
.^'.010
0.003
0.001
,^07012
0.005
—
-tf.010
0.009
—
0.001
—
—
—
—
—
0.090
mg/Nm
JX.-02
0..01
0701
0".01
0.003
0.001
-87 01
0.005
—
sor.oi
0.009
—
0.001
—
—
—
—
—
0.09
4
mg
0.041
0.024
0.018
0.018
0.019
0.003
0.015
0.013
—
0.008
0.012
—
0.013
0.004
0.003
—
—
—
0.19
mg/Nm
0.1
0.08
0.-06
0.06
0.07
0.01
0.05
0.05
~
0.03
0.04
—
0.05
0.01
0.01
—
—
—
0.66
TABLE 4. (Continued)
-------
KAS
Component notation
Anthracene/Phenanthrene ^
Methyl anthracenes \s^
Fluoranthene,./
Pyrene -^
Methyl Pyrene/Fluoranthene
Benzo(c)phenanthrene ***
Chrysene/Benz(a)anthracene *
Methyl chrysenes *
7,12-Dimethylbenz(a)anthracene ****
Benzo fluoranthenes **
Benz(a and e)pyrenes . ***
Perylene
3-Methylcholanthrene ****
Inder.o(1.2,3,-cd)pyrene *
Benzo (ghi)perylene
Dibenzo(a,h)anthracene ***
Dibenzo(c,g)carbazole ***
Dibenz(ai and ah)pyrenes ***
POX
POM Loading
Time Segment: 1
mg
0.32
0.23
0.054
0.049
0.081
0.004
0.033
0.033
— —
0.017
0.023
—
0.013
0.004
0.003
0.007
—
—
0.87
mg/Nm
0.6
0.4
0.09
0.08
0.1
0.007
0.06
0.06
— —
0.03
0.04
—
0.02
0.007-
0.005
0.01
—
—
1.5
Run No. 5
2
mg
0.48
0.41
0.19
0.17
0.11
0.017
0.10
0.031
—
0.019
0.009
—
—
0.001
0.001
—
—
—
1.5
mg/Nm
0.4
0.3
0.1
0.1
0.06
0.003
0.02
0.02
—
0.01
0.007
—
—
0.0007
0.0007
—
—
—
1.1
3
mg
0.45
0.019
0.013
0.098
0.090
0.008
0.073
0.043
—
0.051
0.041
—
0.032
0.023
0.014
—
—
0.019
1.3
mg/Nm
0.6
0.02
0.02
0.1
0.1
0.01
0.09
0.05
—
0.06
0.05
—
0.04
0.03
0.02
—
—
0.02
1.6
4
mg
0.37
0.40
0.076
0.12
0.24
0.15
0.066
0.062
—
0.33
0.62
—
0.51
0.19
0.12
0.15
—
0.066
3.5
mg/Na3
0.2
0.2
0:03
0.05
0.1
0.06
0.03
0.03
—
0.1
0.3
—
0.2
0.08
0.05
0.06
—
0.03
1.5
TABLE 4. (Continued)
-------
U)
Run No. 6
HAS
Component dotation
Anthracene/Phenanthrene
Methyl anthracenes
Fluoranthene
Pyrene
Methyl Pyrene/ Fluoranthene
Benzo(c)phenanthrene ***
Chrysene/Benz (a) anthracene *
Methyl chrysenes *
7,12-Dimethylbenz(a)anthracene ****
Benzo fluoranthenes **
Benz(a and e)pyrenes ***
Perylene
3-Methylcholanthrene ****
Indeno(l,2,3,-cd)pyrene *
Benzo (ghi) perylene
Dibenzo(a,h)anthracene ***
Dibenzo(c,g)carbazole ***
Dibenz(ai and ah)pyrenes ***
POM
POM Loading
Time Segment: 1
mg mg/Nm
0.085
O.OA4
0.020
0.013
0.019
0.0002
0.090
0.042
—
0.025
0.015
—
0.026
0.007
0.005
—
—
—
0.39
0.1
0.06
0.03
0.02
0.03
0.0003
0.1
0.06
—
0.04
0.02
—
0.04
0.01
0.007
—
—
—
0.57
2
mg
0.46
0.44
0.24
0.17
0.16
0.017
0.011
0.045
—
0.039
0.018
—
0.010
0.007
0.006
0.018
—
—
1.75
3
mg/Nm
0.3
0.3
0.2
0.1
0.1
0.01
0.007
0.03
—
0.02
0.01
—
0.006
0.004
0.004
0.01
—
—
1.1
mg
3.48
1.12
1.15
0.70
1.09
0.32
0.36
1.75
—
1.37
1.10
—
1.03
—
—
—
—
—
16.7
mg/Nm3
0.3
0.1
0.1
0.07
0.1
0.03
0.03
0.02
—
0.1
0.1
—
0.1
—
—
—
—
—
1.6
4
Bg
1.31
0.91
0.27
0.19
0.86
0.39
1.68
1.22
—
0.40
0.47
—
0.12
—
—
—
—
—
7.82
mg/Nm3
0.2
0.2
0.-05
0.04
0.2
0.07
0.3
0.2
—
0.08
0.09
—
0.23
—
—
—
—
--
1.5
TABLE 4. (Continued)
-------
Co
HAS
Component Notation
Anthracene/Phenanthrene
Methyl anthracenes
Fluoranthene
Pyrene
Methyl Pyrene/Fluoranthene
Benzo (c)phenanthrene ***
Chrysene/Benz (a) anthracene *
Methyl chrysenes *
7,12-Dimethylbenz(a)anthracene ****
Benzo f luoranthenes **
Benz(a and e)pyrenes ***
Perylene
Kethylbenzopyrcnes ****
lndeno(l,2,3,-cd)pyrene *
Benzo (ghi) perylene
Dibenzo(a,h)anthracene ***
Dibenzo(c,g)carbazole ***
Dibenz(ai and ah)pyrenes ***
POM
POM Loading
Time Segment:
mg
^-0.022
^"0.039
0.0033
0.0036
0.0056
0.0018
XT.'0088
0.0034
—
••tf;010
0.0083
0.0051
—
—
—
—
0.11
1
mg/Nm
0.
0.
0.
0.
0.
0.
0.
0.
—
0.
0.
0.
—
—
—
—
—
0.
07
1
01
01
02
005
03
01
03
03
02
35
Run
2
No. 9
mg mg/Nm
0.010 0.
0.0055 0.
§014 0.
014 0.
0.014 0.
0.0074 0.
^-.035 0.
0.012 0.
—
~tf.031 0.
0.0097 0.
0.0045 0.
—
—
—
—
—
0.16
0.
01
05
01
01
01
007
03
01
03
09
004
15
3
mg mg/Nm
^0043
0.
0.
0.
0.
0.
0015
0014
00060
00070
00035
-0^0024
0.
-
0015
-
^0038
0.
0.
0.
0.
-
-
-
0.
0014
0014
00040
00030
--
-
-
020
H^^H^HMOKW
0.
0.
0.
0.
0.
0.
0.
0.
~
0.
0.
0.
0.
0.
—
—
—
0.
005
002
002
0007
0008
0004
0003
002
004
002
002
0005
0004
022
4
mg
^0082
^0030
0.0021
0.0011
0.0016
0.00085
^.0034
0.0025
—
<>0<0042
0.0021
0.0010
—
—
—
—
—
0.30
mg/Nm
0.003
0.001
0:0008
0.0004
0.0006
0.0003
0.001
0.001
—
0.002
0.0008
0.0004
—
—
—
—
—
0.012
TABLE 4. (Continued)
-------
Run No. 10
. WAS
•Component Notation
Anthracene/Phenanthrene
Methyl "anthracenes
Fluoranr*|or""
-Pyrerie
Methyl Pyrene/Fluoranthene
Benzo (c)phenanthrene ***
Chrysene/Benz (a) anthracene *
Methyl chrysenes *
7 , 12-Dimethylbenz (a)anthracene ****
Benzo fluoranthenes **
Benz(a and e)pyrenes ***
Pcrylene
Methylbenzopyrencs ****
Indeno(l,2,3,-cd)pyrene *
Benzo (ghi)perylene
Dibenzo(a,h)anthracene ***
Dibenzo(c,g)carbazole ***
Dibenz(ai and ah)pyrenes ***
POM
POM Loading
Time Segment: 1
mg
0.0037
0.0018
0.0052
- 0.0053
0.0053
0.0030
0.013
0.0040
~
0.010
0.0032
—
0.0015
—
—
~
~
—
0.056
mg/Nra
0.009
0.004
0.01
-0.01
0.01
0.008
0.03
0.01
—
0.02
0.008
—
0.004
—
—
—
—
—
0.14
2 ,
3
mg . mg/Nm
0.0067
0.0022
0.0035
0.00095
0.0010
0.00090
0.0040
0.0029
—
0.0074
0.0023
—
0.0014
—
—
—
—
—
0.033
0.002
0.0005
0.0008
0.0002
0.0002
0.0002
0.001
0.007
—
0.002
0.006
—
0.0003
—
—
—
—
—
0.008
^••^^VK^^^^^^K
3
mg
0.014
0.030
0.0036
0.0034
0.0070
0.0021
0.011
0.0078
—
0.015
0.0052
—
0.0048
0.0017
0.00060
—
—
—
0.11
.- ... 4
3 3
mg/Nm mg~ mg/Nm
0.01
0.03
0.004
0.003
0.007
0.002
0.01
0.008
—
0.02
0.005
—
0.005
0.002
0.0006
—
—
—
.0. 11
TABLE 4. (Continued)
-------
WAS
Component Notation
Anthracene/Phenanthrene
Methyl anthracenes
Fluoranthene
Pyrene
Methyl Pyrene/Fluoranthene
Benzo(c)phenanthrene ***
Chrysene/Benz (a) anthracene *
Methyl chrysenes *
7 , 1 2-Dine thy Ibenz (a) anthracene ****
Benzo fluoranthenes **
Benz(a and e)pyrenes ***
Perylene
Methylbenzopyrenes ****
Indeno(l,2,3,-cd)pyrene *
Benzo (ghi)perylene
Dibenzo(a,h)anthracene ***
Dibenzo(c,g)carbazole ***
Dibenz(ai and ah)pyrenes ***
PCM
POM Loading
Run No
. 11
Time Segment: 1&2
mg
0.41
0.28
0.10
0.057
0.022
0.014
0.030
0.0061
—
—
—
—
—
—
—
0.92
3
mg/Nm
0.2
0.2
0.06
0.03
0.01
0.008
0.02
0.003
—
—
—
—
—
—
—
0.53
mg
0.26
0.26
0.047
0.069
0.013
0.0089
0.016
0.011
—
—
—
—
—
—
—
0.69
3&4
mg/Nm
0.08
0.08
0.01
0.02
0.004
0.003
0.005
0.004
—
—
—
—
—
—
—
0.22
mg
0.23
0.096
0.14
0.81
0.051
0.065
0.047
0.016
—
0.058
0.031
0.012
0.016
0.015
0.0071
1.6
Run No.
1&2
mg/Nm
0.14
0.06
0.09
0.5
0.03
0.04
0.03
0.01
—
0.04
0.02
0.008
0.01
0.009
0.004
0.81
12
3.<.4
mg
0.28
0.10
0.11
0.068
0.081
0.062
0.10
0.052
—
0.045
0.027
0.019
0.021
0.017
0.014
1.0
mg/Nm
0.09
0.03
0.64
0.02
0.03
0.02
0.03
0.02
—
0.01
0.009
0.006
0.007
0.006
0.005
0.33
TABLE 4. (Continued)
-------
Co
Un
Run No. 13
WAS
Component Notation
Anthracene/Phenanthrene
Methyl anthracenes
Fluoranthene
Pyrene
Methyl Pyrene/Fluoranthene
Benzo(c)phenanthrene ***
Chrysene/Benz(a)anthracene *
Methyl chrysenes *
7 , 12-Dime thylbenz (a) anthracene ****
Benzo fluoranthenes **
Benz(a and e)pyrenes ***
Perylene
Methylbonzopyrenes ****
Indeno(l,2,3,-cd)pyrene *
Benzo (ghi)perylene
Dibenzo(a,h)anthracene ***
Diber.zo(c,g)carbazole ***
Dibenz(ai and ah)pyrenes ***
POM
POM Loading
Time Segment: 1&2
mg
0.096
0.041
0.037
0.017
0.013
0.069
0.026
0.013
—
0.058
0.030
0.0095
0.022
0.013
0.0077
—
—
—
0.46
mg/Nm
0.05
0.02
0.02
0.01
0.007
0.04
0.01
0.007
—
0.03
0.02
0.005
0.01
0.007 •
0.004
—
—
—
0.26
3-5,4
mg
0.11
0.051
0.030
0.024
0.028
0.097
0.048
0.018
—
0.058
0.034
0.010
0.036
0.014
0.0072
—
—
—
0.57
mg/Nm
0.03
0.02
0.009
0.008
0.009
0.03
0.02
0.006
—
0.02
0.01
0.003
0.01
0.004
0.002
—
—
—
0.18
Run No. 14
1&2
mg
0.24
0.13
0.10
0.062
0.042
0.020
0.045
0.023
—
0.037
0.018
0.0068
0.022
0.0046
0.0023
—
—
—
0.74
mg/Nm
0.1
0.08
0.06
0.04
0.02
0.01
0.03
0.01
—
0.02
0.01
0.04
0.01
0.003
0.001
—
—
—
0.44
3.S.4
mg
0.082
0.0057
0.018
0.018
0.034
0.025
0.090
0.11
—
0.035
0.025
0.0081
0.039
0.0096
0.0077
—
—
—
0.56
mg/Nm
0.02
0.02
0.005
0.005
0.01
0.008
0.03
0.003
—
0.01
0.008
0.002
0.01
0.003
0.002
—
—
—
0.17
TABLE 4. (Continued)
-------
WAS
Component Rotation
Anthracene/Phenanthrene
Methyl anthracenes
Fluoranthene
Pyrene
Methyl Pyrene/Fluoranthene
Eenzo(c)phenanchrene ***
Chrysene/Benz (a) anthracene *
Methyl chrysenes *
7,12-Dimethylbenz(a)anthracene ****
Benzo fluoranthenes **
Benz(a and e)pyrenes ***
Perylene
Methylbenzopyrem:s ****
Indeno(l,2,3,-cd)pyrene *
Benzo (ghi)perylene
Dibenzo(a,h)anthracene ***
Dibenzo(c,g)carbazole ***
Dibenz(ai and ah)pyrenes ***
POM
POM Loading
Run
No. 15
Time Segment: 1&2 3&4
mg
0.024
0.014
0.052
0.040
0.045
0.047
0.042
0.019
—
0.046
0.028
0.0019
0.020
0.0078
0.0063
—
—
—
0.41
mg/Nra
0.01
0.008
0.03
0.02
0.03
0.03
0.02
0.01
—
0.03
0.02
0.01
0.01
0.004
0.004
—
--
—
0.23
mg
0.64
0.39
0.22
0.16
0.27
0.079
0.40
0.26
—
0.026
0.017
0.012
0.027
0.0091
0.0058
—
~
—
2.5
mg/Nm
0.2
0.1
0.05
0.04
0.07
0.02
0.1
0.06
—
0.06
0.04
0.03
0.07
0.02
0.01
~
—
~
0.60
Run No. 1
1&2
mg
0.67
0.44
0.44
0.29
0.33
0.18
0.14
0.073
~
0.048
0.028
0.017
0.037
0.0056
0.0066
—
~
~
2.5
mg/Nm
0.3
0.2
0.2
0.1
0.1
0.07
0.05
0.03
—
0.02
0.01
0.007
0.01
0.002
0.003
—
—
—
0.98
6
344
mg
0.42
0.29
0.12
0.13
0.27
0.49
0.29
0.26
—
0.028
0.022
0.026
0.042
0.0072
0.0056
—
—
—
2.0
mg/Nm
0.1
0.08
0.03
0.04
0.08
0.1
0.08
0.08
—
0.08
0.06
0.08
0.01
0.002
0.002
—
—
—
0.58
TABLE 4. (Continued)
-------
TABLE 4. (Continued)
to
Run No. 17
HAS
Component Notation
Anthracene/Phenanthrene
Methyl anthracenes
Fluoranthene
Pyrene
Methyl Pyrene/Fluoranthene
Benzo(c)phenanthrene ***
Chrysene/Benz (a) anthracene *
Methyl chrysenes *
7, 12-Dime thy Ibenz (a) anthracene ****
Benzo fluoranthenes **
Benz(a and e)pyrenes ***
Perylene
Methylbenzopyrenes ****
Indeno(l,2,3,-cd)pyrene *
Benzo (ghi)perylene
Dibenzo(a,h)anthracene ***
Dibenzo(c,g)carbazole ***
Dibenz(ai and ah)pyrenes ***
POM
POM Loading
Time Segment: 1 &2
fflg
0.99
0.35
0.12
0.22
0.63
0.077
0.37
0.14
—
0.025
0.010
0.016
0.014
0.0034
0.0021
—
—
—
3.0
mg/Nm
0.6
0.2
0.07
0.1
0.4
0.04
0.2
0.08
—
0.01
0.006
0.009
0.008
0.002
0.001
—
—
—
1.7
3&4 3 4
mg
0.92
0.78
0.37
0.27
0.55
0.081
0.067
0.065
—
0.068
0.044
0.015
0.018
0.0055
0.0032
—
—
—
3.3
333
mg/Nm mg mg/Nm mg mg/Nm
0.5
0.4
0.2
0.2
0.3
0.05
0.04
0.04
—
0.04
0.03
0.009
0.01
0.003
0.002
—
—
—
1.9
-------
COAL COMBUSTION ON THE FUEL BED
The fuel bed was observed (through the stoker firedoor) for brief
periods of time throughout each of the runs listed in Table 2. It was
observed that for all coals except anthracite, the fuel bed and the resulting
flame and flow patterns were continuously changing during the runs. Accord-
ingly, it is anticipated that emission levels would also vary to some degree
throughout each run and from one run to another (as for Run 1 and replicate
Runs 2 and 8 of Table 3). Emissions data were collected over 4 to 6 cycles
of operation which tended to lessen the effect of these variations, thus,
"average" emission levels were determined. Some general observations are
discussed below for each of the coals.
High Volatile Bituminous Coal
In general, this coal tended to cake, creating a nonuniform air
distribution through the bed. The 20-minutes-on/40-minutes-off cycle did
not allow the fuel bed to become sufficiently hot to burn out the tars.
These tars became plastic and cemented pieces of coal together, forming cakes
of various sizes that retarded the even distribution of air through the fuel
bed. The caking was less severe during the 50-minutes-on/10-minutes-off
cycle of Run 3. However, during Run 3 it was observed that once the bed
began to cake, the burning rate became extremely variable. During the
initial "on" period (Time Segment 1), coal fed into the retort would not
burn uniformly and completely as there was a deficiency of air. As the
bed became hotter during the latter part of Time Segment 2, this unburned
coal (as well as the coal being fed into the retort) would ignite, resulting
in an increase in the burning rate. This observation was verified by the
fact that excess oxygen level of the flue gases was varying for a constant
combustion air flow rate.
An important aspect of the high-volatile bituminous coal runs are
the relatively high particulate and POM loadings during the off period
(Time Segments 3 and 4). Smoke was visible from the stack only during
this period (except during the last two cycles of Run 1 in which the fuel
bed degraded noticeably) and was most noticeable (about a Ringelmann 1)
during the 5-minute period after stoker shutdown (Time Segment 3). During
the off-period (Time Segments 3 and 4), the CO levels were greater than
1250 ppm; they were less than 500 ppm during the on-period. It is conjectured
that the high particulate and POM loadings during the off-period are attri-
buted to the incomplete combustion of tars emitted from this volatile coal.
This can be further evidenced by the plugging (apparently by condensible
tars) of the filter during Time Segment 4 of the first cycle in both Runs 1
and 2
Low Volatile Bituminous Coal
The low volatile bituminous coal fired in Run 6 has high caking
properties. This coal tended to cake into large masses that interfered
with the overfire air. Because of its relatively low volatile content, this •
bituminous coal could be considered a natural smokeless as Bacharach smoke
levels of approximately 4 and 9 were measured during the on- and off-periods,
38
-------
respectively. The excess air levels varied considerably during this run,
indicating a varying burning rate and nonuniform fuel bed.
Processed "Smokeless" Coal
This lignite char was soft and broke into fines as it was conveyed
by the feed screw to the retort. As a consequence, there was an excessive
amount of fines burning as sparklers above the bed. In addition, the coal
fines appeared to mat the fuel bed somewhat. It is conjectured that these
coal fines contributed significantly to the particulate loadings in Time
Segments 1 and 2 of Run 4. Particulate loadings were low during the off-
period although CO levels were greater than 1250 ppm. This process coal was
truly "smokeless" as it was fired smokelessly without overfire air.
Western Subbituminous Coal
This coal had a slight tendency to cake forming small, but visible,
blowholes in the fuel bed. Although overfire air was required to achieve smoke-
less operation, Bacharach smoke levels less than 2 were measured during portions
of the "on" cycle. Bacharach smoke numbers greater than 9 were measured
during the off-period, although no visible smoke could be detected from the
stack. (These spots had a yellowish tint, however, and it was difficult
to visually determine the Bacharach smoke number.)
Anthracite
Unlike the other coals, the anthracite did not cake nor did the ash
fuse into a clinker. As a consequence, the fuel-bed conditions remained stable
for over 24 cycles of operation. The anthracite coal was noticeably more
difficult to ignite than any of the other coals. However, once ignited, this
fuel bed burned uniformly with a blue flame. Overfire air was not used yet
Bacharach smoke numbers were less than 1. It is anticipated that the use of
overfire air could have reduced CO levels.
FACTORS INFLUENCING EMISSION LEVELS
In general, the particulate, POM, and smoke emission levels appear
consistent in that the higher particulate levels correspond to higher POM
and smoke levels. The exception is the particulate level of the processed
lignite char; however, the relatively high particulate loading obtained with
this coal is attributed to the excessively large amount of fines fed into
the fuel bed. The particulate emission levels summarized in Table 5 are
within the range of those reported in the literature (7). Likewise, S02
and NO emission levels are within the range of those reported. Although
there are no POM emission data from stokers in the literature (utilizing
the sampling and analytical techniques of this research), it is observed
that levels of POM generated from steady-state firing of the stoker are
significantly higher (at least several orders of magnitude) than those
generated from steady-state operation of oil-fired equipment (8). Previously,
POM data were reported as benz(a)pyrene (9), only one of the approximately
18 species that are currently scanned for during analysis. In addition, some
of the POM emission levels that have been reported in the literature, use
39
-------
TABLE 5. THE EFFECT OF VOLATILE MATTER AND FREE SWELLING INDEX ON
PARTICIPATE AND POM EMISSIONS FROM COAL COMBUSTION DURING
A 20-MINUTE-ON/40-MINUTE-OFF CYCLE AND CONTINUOUS FIRING
RATES OF 45 TO 67 LB/HR (20 TO 30 Kg/hr)
Run
1
2
6
5
7
4
9
Volatile
Coal Matter
High volatile bituminous
High volatile bituminous
Low volatile bituminous
Western subbituminous
Western subbituminous
Processed lignite char
Anthracite
40
40
21
37
37
16
4
Particulate
Free Emissions.
Swelling g/lb9
27 4
10 3
5
1.8 4
0.86 1/2
(a) 1 g/lb = .454 g/Kg and 1 mg/lb = .454 ng/Kg.
-------
the BaP emission as a key to which a constant factor is applied to predict
total POM levels. The data contained in Table 4 indicate this method of pre-
dicting total POM is somewhat questionable, as the ratio of the BaP emission
to the total POM emissions varies considerably.
Because of the inherent scatter of stoker-coal combustion data,
the complex interrelation among the factors that affect coal combustion,
the limited amount of data, specific correlations and/or quantitative relations
could not be identified that could be substantiated by the data. However, the
data suggest that certain coal properties and stoker operating factors do
influence emissions.
Coal Properties
Particulate and POM emission levels are related to the chemical
and physical properties of the coal that affect the combustion processes
of these coals. As an example, particulate can consist of unburned carbon
(which related to volatile content of the coal). fly ash (which relates to
ash content and coal size), and condensible tars (which relates to volatile
content) .
Volatile Content—
As indicated in Tables 1 and 2, coals with the higher volatile
content generally produced higher levels of particulate and POM. These
higher emission loadings are attributed to the incomplete combustion of the
tars emitted from the coal. This can be further evidenced by the relatively
high emission loadings for the off cycle, where conditions inhibit the burnout
of tar (low-bed temperature and insufficient supply of air to the fuel bed).
The differences in the particulate loadings of each of the coals were con-
siderably less during the "on" cycle than in the "off" cycle.
Free-Swelling Index—
The free-swelling index is a measure of the caking property of the
coal. The fuel bed of a caking coal generally degrades over a period of
time as large fissures form in the bed, separating masses of coke of various
sizes and preventing the even distribution of air through the fuel bed. Thus,
the coals with the highest free-swelling index had the highest particulate
and POM emissions levels.
Coal Size—
Some undersize fines [less than 1/4 in. (6.4 mm)] are unavoidably
formed during crushing, screening, and feeding of coal. Less than 15
percent fines is acceptable (and may be beneficial in uniform feeding) while
greater than this amount interferes with uniform air distribution. In
addition, an excessive amount of fines can result in coal particles being
lifted from the bed. Although these coal particles burn, the remaining ash
is emitted to the stack. Run 4 is an example of this as a significant
amount of coal fines were burned above the bed resulting in a relatively
high particulate loading during the "on" cycle. It is thought that this
high particulate loading was attributed to fly ash rather than resulting
from incomplete combustion of the coal as suggested by the relatively low
POM loading during the "on" cycle.
41
-------
Ash Content—
The ash content has secondary effects in generating particulate
emission. A substantial portion of the ash should remain in the fuel bed.
However, the properties of this ash can be important in the overall per-
formance of the stokers. For example, a low-ash fusion coal could create
clinkers that interfere with the uniform feed of coal and distribution of
air. From Tables 1 and 7 it is noted that the coals with the lowest ash
content generated the highest particulate loading, thus suggesting that
other factors (rather than ash content) are the concomitant indicators
in predicting particulate loading from stoker combustion.
Certain properties of the ash may also have an effect on other
emissions. For instance, the relatively high lime content of ash in some
of the Western coals can react with the sulfur and, thus, reduce the
conversion of fuel sulfur to sulfur oxides. However, a complete coal
and particulate analysis is required to verify the extent of the effect
of ash content on both gaseous and solid emissions.
Effect of Firing Rate
Both the high volatile bituminous and the Western subbituminous
were fired at rates corresponding to low-, mid-, and full-boiler capacities.
For the Western coal, it appears that firing rate has no significant effect
on particulate and POM emissions. For the high volatile coal, there appears
to be no appreciable differences among the particulate loadings during the
"on" cycle for the 3 firing rates. However, the unexpectedly lower POM
loadings and particulate loadings during the "off" cycle ofRuns 12 and 13,
as compared to Runs 1 and 2, are somewhat perplexing. Apparently, the fuel
bed condition (a controlling factor during the "off" cycle) of these runs
was considerably different. Additional data points are required to verify
the results.
Effect of Cycle
From Tables 2 and 3, comparing Runs 1 and 2 with Run 3 for the
high volatile coal, and Runs 9 and 10 for anthracite, the duration of the
"on" period within a cycle did not have any significant effect on POM
and particulate emission. Additional data are needed to determine whether
differences in emission levels of these runs are real or are a result of
the scatter of the data.
Effect of Overfire Air
Overfire air was necessary to achieve smokeless operation on the
coals with volatile matter greater than 20 percent. During the checkout
runs, the high volatile bituminous coal was fired with and without overfire
air. Particulates were sampled for 60 minutes during steady-state firing.
The particulate loadings were nearly identical (being 130 mg/Nm^ without
the overfire air and 140 mg/Nm^ with the overfire), although the Bacharach
smoke levels were 4 with the overfire air and greater than 9 without.
Apparently, the smoke contributes a negligible amount to the overall
particulate loading. Analysis of the filter from both runs indicated that
42
-------
approximately half the catch was unburned carbon. Thus, overfire air had
an appreciable influence on smoke emission, but had apparently no influence
pn particulate emissions.
Effect of the Modified Cycle Operation
During the checkout runs, it was observed that the smoke emissions
and the condition of the fuel bed could be controlled by controlling the
amount of both the primary and secondary air during the operating cycle.
Normally, once set up and adjusted, the residential and small commercial
stoker operates at one speed with both the combustion air fan and feed
screw operating concurrently. As a result, during the initial "on" period
there is an excessive amount of air (Time Segment 1) and during the initial
"off" period (both feed screw and fan off) there is a deficiency of air
(Time Segment 3). Accordingly, the stoker operation was modified to achieve
a better control of air during these periods by (1) during initial "on"
period the primary air flow was reduced to 200 Ib/hr (91 Kg/hr), approximately
30 to 40 percent of the normal flow rate for the first 5 minutes, and (2)
during the initial "off" period the overfire air jets remained on for 5
minutes.
For the high volatile bituminous coals, this modification signi-
ficantly reduced the POM emissions (by a factor of 7) and reduced to a
lesser extent the particulate emissions (by a factor of 2.3) (comparison
of Runs 1, 2, and 17). However, for the Western coal, this modification
had no significant effect on either the particulate or POM emissions (com-
parison of Runs 5 and 16). During the normal (not modified) operating
cycle, visual observations indicated that combustion in and above the fuel
bed was extremely nonuniform for the high volatile bituminous coal and
considerably more uniform for the Western. (The particulate and POM
emissions measurements confirm this observation.) Visual observation of
the fuel bed during operation on the modified cycle indicated that the fuel
bed was noticeably more uniform for the high volatile bituminous coal while
the modification had no noticeable effect on the fuel bed condition for the
Western coal run. Apparently, this type of modification would not improve
the burning of good stoker coals (such as the relatively uniform and free-
burning Western coal).
OVERVIEW OF EXPERIMENTAL RESULTS
This experimental research demonstrated that smokeless operation
of small commercial stokers can be achieved with minor modifications in the
stoker design (provision for overfire air) and accurate control of the
combustion air. Further, the data indicate that a relatively large amount
of particulate and POM emissions are generated during the off-cycle in
which there is no control of the air supply. It is possible that emissions
can be reduced during this cycle by maintaining a control of the air flow
to and above the fuel bed.
From both the analysis of the data and visual observations of the
fuel bed, it appears that of the coals evaluated, anthracite is the most
43
-------
suitable for stoker firing; however, this coal is limited in supply.
Similarly, the processed coal appears attractive as a stoker fuel provided
it can be manufactured for this type of stoker firing. Also, the Western
subbituminous coal is a candidate coal for stokers, provided that minor
modifications are included in the design and operation of the stokers and
that it can be supplied economically to the Eastern market. The two coals
least suited for stoker firing (the high- and low-volatile bituminous) are
those with the highest volatile matter content and highest free swelling
index. Unfortunately, the supply of these coals is abundant near the largest
potential market areas. These coals are more suited to the larger industrial
spreader stoker boilers and/or the pulverized coal utility boilers.
SECTION 9
ASSESSMENT OF THE POTENTIAL FOR STOKER COAL UTILIZATION
The assessment of the advisability of increased utilization of
coal for residential and small commercial stoker applications includes
consideration of boiler-operating efficiency, fuel type and availability,
economics, emission assessment, and public acceptance. This assessment
is based on the findings of the stoker and processed coal surveys, and the
experimental research investigation.
Operating Efficiency
Because of the difficulty in obtaining an accurate energy balance
on a small commercial stoker-fired hot water boiler system, a meaningful
boiler-operating efficiency could not be determined. A review of the stoker
literature also verified that true cyclic efficiency values (not steady state
values for continuous firing) are not readily available for stokers or oil/gas
fired systems in the size range of interest. However, qualitative comparisons
of operating efficiencies (based upon relative differences in excess air levels
and stack-gas temperatures) of stokers with those of oil-fired residential
systems observed by Barrett, et al (3) suggest that stoker and oil-fired 'sys-
tems operate with about the same overall efficiency (at approximately the
same boiler load). Both types of systems operate at excess air levels that
approach 100 percent with stack-gas temperature above 500 F (260 C).
It appears that the potential exists to increase efficiency through
modifications.in burner-boiler designs, but this appears to be more readily
achievable in a gas- or oil-fired system. In addition, for coal-fired systems,
selection of a coal that minimizes soot deposition on heat transfer surface
is necessary to maintain efficiency. For example, the combustion of the
high volatile bituminous coal deposited about a 1/8 in. (3.2 mm) layer of soot
in the fire tubes after several days of operation, resulting in a stack-gas
temperature rise of 100 F (30 C) in that period. On the other hand, the
combustion of anthracite deposited only a thin layer (less than 1/32 (0.8 mm)
of soot after several days of firing, resulting in a stack-gas temperature
rise of about 40 F (22 C).
44
-------
Efficiency has not been an important consideration in this size of
equipment. Although the increasing costs of all fuels makes efficiency a
more significant factor in combustion equipment design and operation, it
may not be as important a consideration in stoker systems as in oil or gas
systems because coal is a relatively more abundant resource than oil or gas.
Fuel Type and Availability
Eventually, our oil and natural gas supplies will be depleted so
that alternative methods for residential and small commercial space heating
applications will have to be identified. Because residential and commercial
installations have been considered high priority users, there appears to be
no large curtailment of supply of oil and gas to these users in the immediate
future. Where oil and gas have not been available and operating cost is
not a major issue, electricity frequently has been used for space heating.
The long range supply of energy for space heating is unclear. In twenty
years, when our supply of oil and gas may become critical, gasified or
liquefied coal, advanced heat pumps, solar energy, and other advanced con-
cepts may be developed to the point that they compete with stokers.
In addition, the fuel type and availability of the coal itself
is another consideration. The experimental research indicated the most
environmentally suitable coals for stoker firing are those that are low
sulfur and free burning (noncaking). However, these properties are not
characteristic of coals in abundant supply and/or located near the highest
potential market area. (Attempts to minimize the caking tendencies of low-
sulfur caking coals, such as those found in West Virginia and Eastern
Kentucky within the stoker-boiler system never fully developed (10).)
Accordingly, there appears to be a potential market for processed fuel that
has low sulfur, low volatile matter, and is free burning.
Economics
In comparison to oil- and gas-fired systems, stoker-fired systems
for residential and small commercial space heating applications (less than
1 million Btuh input) are economically unattractive. The stoker itself
can cost two to three times more than comparable oil and gas burners (based
on a communication with a burner manufacturer). In larger size equipment,
this difference is not as great, and in some systems, the capital costs of
a stoker may be lower than those of oil and gas burners. In addition, the
stoker requires a more elaborate boiler setting, larger floor area, and an
area for coal storage—all adding to the installation costs.
Fuel costs must also be considered. These costs vary from region
to region and have become difficult to predict. A check on the current fuel
prices in Columbus, Ohio, indicates little difference among the energy costs
of stoker coal, fuel oil, and natural gas with natural gas being the least
expensive. Also with natural gas and fuel oil, there are no costs associated
with fuel handling and ash disposal. However, it is anticipated that in the
future, costs of natural gas and fuel oil will be increasing at a faster rate
than for stoker coal, making stoker firing more economically competitive.
-------
Emission Assessment
Because the emissions from stoker-fired equipment are significantly
higher than those from oil- or gas-fired equipment, an increase in utilization
of coal for residential and small commercial space heating equipment will have
a significant impact on the environment. Stokers emit pollutants at low
atmospheric levels and, thus, the pollutants are not easily dispersed. In
addition, residential and small commercial stoker installations would be
concentrated in high population density areas, further adding to the dispersion
problem. It is anticipated that in addition to using low sulfur coals, stoker-
boiler systems should be required to include a mechanical collector on the
stack to control particulate emissions. Alternatively, utilizing electricity
rather than oil or gas would lower (slightly) the emissions around the site
of the installation, but the emissions from the new power plants would have
to be considered. However, these emissions could be more economically
controlled.
The increased utilization of stoker coal creates additional emissions
associated with delivery of the coal and the removal of the ash that are not
present in gas- and oil-fired systems. A negligible increase in vehicular
emissions would be anticipated in regard to this aspect.
Public Acceptance
Stoker firing for space heating would not be acceptable to the
American public unless there were no other alternatives available or these
alternatives were economically unattractive. They are accustomed to the
convenience, dependability, and cleanliness of utilizing oil and gas. Factors
that contribute to the unattractiveness of stoker firing include:
• Storage area required
• Ash disposal problems
• Uncleanliness
• Environmentally unattractive
• Increased maintenance
• Overheating of residence during some periods of early fall
and late spring. (The fuel bed serves as a pilot and must
be kept alive by operating the stoker even though heat is
not required.)
• Larger temperature excursions. [It is not practical to
operate stokers with short "on" times of 4 to 5 minutes,
as some oil- and gas-fired burners operate (3)].
However, it must be remembered that the majority of residential and small
commercial space heating equipment was coal-fired as late as 25 years ago.
It was accepted then and will be accepted again if no viable alternative
can be identified.
-------
General Overview
In summary, the current economic and environmental factors
associated with stoker firing are unfavorable for increased utilization
of coal in residential and small commercial space heating applications.
Although our supplies ;of fuel oil and natural gas are dwindling, there
appears to be no immediate or near term shortage for the vast majority of
small users. Where shortages exist, electric space heating coupled with
extensive insulation, rather than stoker firing, will be selected as the
alternative. '
In the event Ithat there is an increase in the utilization of stokers,
stoker designs need to foe modified and processed coals need to be made more
marketable as current Designs and the fuels that are most readily available
would not be attractive from the operational and environmental viewpoints.
47
-------
APPENDIX A
SURVEY OF STOKER-BOILER MANUFACTURERS
The renewed interest in coal as a fuel for space heating, created by
the current shortages in heating oil and natural gas, has even penetrated
into the residential and small commercial space heating applications.. As late
as the 1950's coal was still used as a major fuel for these applications but,
thereafter, was rapidly displaced by gas and oil. With the decline in coal
use, there was an accompanying decline in the number of stoker and boiler
manufacturers until only one major manufacturer and only a few boiler manufac-
turers remained. However, the recent oil embargo has renewed interest in
these stoker-boiler systems.
OBJECTIVES
The objectives of this stoker survey were
• To identify the stoker-boiler systems most commonly
used in the 5 - 20 x 104 Btuh (52 - 210 MJ/hr) range
• To identify the stoker-boiler systems most commonly
used in the 2 - 10 x 105 Btuh (210 - 1050 MJ/hr)
range
• To identify the types of fuels that stoker-boiler
systems are capable of burning
• To identify the types of heating systems commonly
used with stokers
• To assess the potential market area for stoker coal
in these size ranges.
In addition, to provide background information, emission factors of
stokers and the stoker-boiler population are discussed.
-------
SUMMARY
The findings from the survey of over twenty present or past manu-
facturers of residential and small commercial stoker-fired space heating ,
equipment (or their representatives) include
• Residential and small commercial stoker-boilers are
similar in;design as systems components are scaled
(up or down) to match the desired range of operation.
The stokers are of the underfeed type.
• The conventional underfeed bituminous stokers are
capable of firing most coals except anthracite.
• The conventional underfeed anthracite stokers are
designed to fire anthracite only. There is a
possibility that this stoker could fire "smokeless"
or processed coal if properly sized.
• There is only one manufacturer of the conventional
anthracite'stoker and only one manufacturer of the
conventional bituminous stoker in the size ranges
of interest. One additional manufacturer makes an
anthraciteistoker that is an integral part of the
boiler system.
• There are pnly three major manufacturers (H. B. Smith,
Kewanee, and Weil McLain) of boilers suitable for
stoker firing. Of these, only Weil McLain currently
manufacturers a boiler in the residential size range.
• There are over 200,000 living units heated by anthracite.
• There has been renewed interest in stoker firing in
the size ranges of interest. The majority of activity
has been for small commercial applications rather than
residential.
• The majority of the new stoker-boiler systems are
designed for hot water, while most replacements
are for steam systems. There has been some renewed
interest in residential stoker-fired warm air furnaces.
49
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EMISSION FACTORS
Table 6 summarizes the emission factors of residential and small
commercial fossil-fuel combustion equipment for space heating application
(11). As noted, the particulate and sulfur dioxide emissions are signi-
ficantly higher for coal combustion than for distillate fuel oil or natural
gas combustion, especially considering that coal can have an ash content as
high as 20 percent and a sulfur content as high as 4 percent.
To minimize emissions from coal-fired equipment in this size range
necessitates the utilization of a low-sulfur, low-ash coal. Whereas fuel
oil can be desulfurized before firing, there are no commercial viable methods
for treating or preparing coal (other than washing) to reduce emissions of
S02- For particulate control, it is conceivable that a mechanical collector
could be utilized in the stack to collect a substantial amount of particulate.
Although Table 6 does not include smoke emission, smoke levels
from stokers can be high (visible smoke from the stack) especially for the
few minutes after stopping the stoker. This smoke problem can be minimized
by modification of the stoker-boiler system to provide a better control of
the combustion air.
POPULATION OF SPACE-HEATING EQUIPMENT
Residential Equipment
Table 7 lists an estimate of (1) the sales, and (2) the number
of units in operation of all automatic space-heating equipment in the
residential size range from 1941 through 1969(12). As noted, stoker
sales have been decreasing since 1946 and recently have accounted for less
than 1 percent of sales. Likewise, the number of stokers in operation has
been continually declining. (These numbers are for automatic heating equip-
ment and do not reflect the number of hand-fired coal units still in operation.)
About 23 percent of these automatic space-heating units are utilized in steam
or hot water systems (13).
50
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TABLE 6.
EMISSION FACTORS FOR FOSSIL FUEL COMBUSTION
(ID
Particulates
lb/106 Btu
Sulfur
Oxides
Btu
Carbon
Monoxide
lb/106 Btu
Hydrocarbons
lb/lQ6 Btu
Nitrogen Oxides
Btu
Coal - Bituminous
Stoker
Hand-fired
- Anthracite
Hand-fired
Distillate oil
Natural gas
0.08
0.8
0.4
0.007
0.019
1.525
1.525
1.525
0.955
0.0006
0.40
3.6
3.6
0.031
0.020
0.12
0.80
0.10
0.02
0.008
0.14
0.07
0.07
0.08
0.08 to 0.120
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TABLE 7.
AUTOMATIC HEATING TRENDS
ANNUAL SALES
OPERATING AT
' , of total
Total
1941 652,591
1942 225,041
1943 64,465
1944 102,028
1945 321.693
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
I960
1961
,336,316
.271,679
803,222
,281,706
,210,725
,346,794
,544.160
.636,812
698 459
,974.282
.809,508
,579,088
.739,865
>, 061 ,632
,816,962
916.078
1962 2,048,396
1961 2,194,619
1964 2,313.462
1965 2,271,303
1966 2,152,252
1967' 2. 196. 853
1968* 2,267,917
1969 2,318,746
Stoker
28.0',:,
35.1
27.5
31.0
37.1
13.5
4.9
9.5
1 T
I.I
1.4
1.2
8.0
0.8
0.7
0.8
0.8
0.7
0.7
0.6
0.5
0.5
0.4
0.3
0.2
-t
Oil-
hiinifrs
51 1'.,
44.2'
51.9
48.9
45.2
37.0
69.8
56.7
47.9
45,6
50.1
50.4
50.3
43.4
41.0
18.2
36.7
32.7
30.8
26.9
26.1
21.1
23.7
21.8
24.0
26.6
26.1
27.2
25.9
Cas-
biirncrs
20.9';.
20.6
20.6
20.1
17.7
49.5
35.3
33.8
49.7
53,3
48.5
48.4
48.9
55.7
58.3
60 0
62.7
Mv 6
64.1
65.5
63.4
61 . 5
64.0
61.1
60.2
59.3
63 . 3
61.3
60.7
Elec-
tric
1941
1942
1943
1944
1945
946
1947
948
949
1950
951
952
1953
954
1955
1956
1957
958
1959
7.0 I960
10.0 1961
14.9 1962
13.6 1963
14.8 1964
15.6
14.1
10.6
11.5
13.4
965
966
967*
968'
969
Total
4,514,627
4,615,785
4,633,755
4,700,130
4,979.775
6.009,347
7,133,709
7,752,498
8,845,695
10,434,971
11,506,701
12,757,700
14,085.664
15,423,130
17.047,244
18,542.422
19.516.099
20,742.043
22,697.083
23,978.635
25,341,538
26,1 M>, 143
27,393.864
28,691,440
29,779,905
31,115,265
32,238,332
33,086,838
33,990,645
END OF YEAR
'', of total
Stoker
17.8'.,
19.0
19.3
19.7
20.7
19.3
16.6
16.0
14.0
11.3
9.8
8.5
7.1
5.8
4.6
4.0
3.5
2.9
2.4
2.1
1.9
..t
. .t
. t
..t
.t
Oil-
hiirners
53.2',,
51.7
51.3
50.9
50.5
47.0
51.2
51.3
50.8
49.6
49.6
49.7
49.8
49.2
48.5
47.3
46.3
45.0
42.5
40.9
39.2
38.5
37.2
36.1
35.3
34.4
34.0
33.5
32.9
Cnx-
htirners
29.0',.;
29.3
29.4
29.4
28.8
33.7
32.2
32.7
35.2
39.1
40.6
41.8
43.1
45.0
46.9
48.7
50.2
52.0
52.5
54.0
55.3
57.5
58.2
58.5
58.2
58.6
58.5
58.6
58.8
Elec-
tric
3.0
3.6
4.0
4.6
5.4
6.5
7.0
7.5
7.9
8.3
* Kcviscil.
t Sinker Hguies ilroppul; less llian I', of aulnnuilic healing.
52
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Small Commercial
Table 8 estimates the boiler population by number, total design
capacity (10^ Btu/hr), and annual load factor times total design capacity
(10^ Btu/hr) as a function of fuel type for the small commercial size
ranges (13).. The annual load factor times the total design capacity gives
the total fuel consumption. From Table 8 it is noted that stoker boilers
comprise about 12 percent of the total number of boilers and comprise about
14 percent of the total fuel consumption in this size range. Nearly all of
these boilers are of the fire-tube type and recent sales data indicate about
80 percent are Scotch. It should be noted that in the size ranges up to
5 x 10" Btu/hr, warm air units are making strong inroads into steam and hot
water unit sales (13).
STOKER-BOILER SYSTEMS
Table 9 summarizes the currently available stokers. Because
anthracite differs in combustion characteristics from bituminous coals, a
different stoker design is required to burn this coal successfully. The
anthracite and bituminous coal stokers are basically the same except in
retort design. The bituminous retort is built to burn efficiently a coal
relatively high in volatile matter and to fuse ash into a removable clinker;
the anthracite stoker retort, on the other hand, is built to burn efficiently
coal of low volatile content and to spill ash into a pit or to the receiver
for the ash. Also because anthracite burns with a slow uniform flame, it
requires less combustion space than bituminous coals.
Table 10 summarizes the currently available boilers suitable for
stoker firing. Cast iron boilers require assembly at the installation site
which is an added expense. This type of boiler has the advantage in that it
can be installed in existing structures that have limited access to the
"boiler room". The steel boilers are packaged boilers that are factory
assembled.
Stokers
The Will-Burt Company is currently the only manufacturer of
bituminous coal stokers in the size ranges of interest. These stokers
are capable of firing most coals except anthracite. Will-Burt's product
line includes stokers with capacity ranging from 20 Ib/hr to 250 Ib/hr.
They have been selling about 500 new stokers per year.
The Van Wert Manufacturing Company is currently the only manu-
facturer of anthracite stokers in the size range of interest. These
stokers could possibly fire a process coal if it were suitably sized.
Van Wert's product line includes anthracite stokers with capacity ranging
from 12 to 100 Ib/hr. They have sold only a few units in the past year.
The Axeman-Anderson Company manufacturers an "Anthratube" unit that
is an integral stoker-boiler system. The anthracite stoker is designed as
53
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TABLE 8. ESTIMATE OF BOILER POPULATION
FOR SMALL COMMERCIAL UNITS (A-3)
Design Capacity, Etu/hr
Coa 1 Tvpc
Stoker coal
Pulverized coal
Residual oil
Distillate oil
0.5-l.OxlO6
Commercial
4,910
4,910
1,498
0
0
0
5,261
5,261
1,289
19,992
19,992
4,118
l-2x!06
Commercial
3,387
6,774
2,066
109
218
92
3,496
6,992
1,713
13,547
27,094
5,581
Nonuatural gas
Natural gas
Sum
Percent stoker
0
0
0
11,644
11,644
3,703
41,807
41,807
10,608
11.7
11.7
14.1
0
0
0
7,866
15,732
5,003
28,405
56,810
14,455
11.9
11.9
14.2
(a) Top number in each group is boiler population by number
count. Second number is the total design capacity
(in 106 Btu/hr) of all boilers, that is, the number
count times the design capacity of a single unit.
The third number is the annual use, that is, the total
design capacity of all boilers in the group times the
average annual load factor.
54
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TABLE 9.
STOKERS
Type
Conventional
'bituminous
Conventional
anthracite
Anthratube
Manufacturer
Will Hurt Co.
Van Wert Mfg.
Company
Axeman-Anderson
Capacity
Ib/hr
20
75
100
12
60
15
30
Cost,
dollars
900
1300
1800
511
800
1000 (b)
Characteristic
Burns most coals except
anthracite
Possibility of burning
"smokeless" coal in
addition to anthracite
Stoker integral part of
boiler. Stoker will not
mate with other boilers.
(a) Oral quotes as of January 1, 1975. Does not include freight charges.
i
(b) Also includes boiler.
TABLE 10. BOILERS
Type Manufacturer
Cast-iron Weil-McLain
Cast-iron H. B. Smith
Steel tube Kewanee , .
Model
K-257
HK-40-6
3R-1
3R-5
Rating(a)
Btu/hr Output
157,000
1,080,000
243,000
750,000
324,000
648,000
Cost.Cb)
dollars
800
3,000
1,130
2,200
2,400
2,700
(a) Based upon 75 percent efficiency and 12,000 Btu/lb coal.
(b) Oral quotes as of January 1, 1975. Does not include freight charges.
55
-------
part of the boiler and will not mate with any other boiler. This system also
utilizes an induced-draft fan. Axeman-Anderson currently markets boilers in
two size ranges, 130,000 Btu/hr and 260,000 Btu/hr, but tandem units can be
used for up to 1,000,000 Btu/hr.
Boilers
Only three major manufacturers (Weil McLain, Kewanee, and H. B.
Smith) of boilers for stoker firing were identified that have an extensive
sales network. Of these only Weil-McLain markets a stoker boiler in the
residential size range. Other boiler manufacturers, such as Van Wert and
Axeman-Anderson, do market stoker boilers, but their market area is limited
to a local region.
RECOMMENDATIONS
From the findings of the survey, it was recommended that both an
anthracite (60 Ib/hr) and a bituminous (75 Ib/hr) stoker be purchased and
mated to a Kewanee 3R-5 boiler. It was felt that, because the residential
and small commercial stokers were so similar in design, only one boiler size
was required to give representative results over the two boiler output ranges
of interest. In addition, to obtain satisfactory combustion of anthracite,
a stoker specifically designed for anthracite was required.
56
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APPENDIX B
SMOKELESS COAL SURVEY
In comparison to oil and gas, high volatile bituminous coal has
been difficult to burn without any visible smoke. Converting this class of
coal into a form in which it would not produce visible smoke, no matter how
it was fired, was of major importance in the 1930's and 1940's when smoke
ordinances were limiting the amount of volatile matter in solid fuels.
Now, with the shortage of oil and gas and with the presence of air pollution
regulations, there has been a renewed interest in "smokeless" coal.
This survey examines the characteristics, manufacturing methods,
and short- and long-term availability of processed smokeless solid fuels and
provides background for assessing the suitability of these fuels for use in
small stokers.
In addition to the smokeless coal survey, this appendix discusses
the selection and acquisition of the other classes of coals used in the experi-
mental investigation.
OBJECTIVES
The major objectives of this survey was to conduct a survey of
the .manufacturing process for "smokeless" coal. Factors to consider
included
• Suitability for stoker-firing
• Environmental impact (both the combustion and
manufacturing aspects)
• Analysis
• Long- and short-term availability
• Economics of smokeless coal utilization.
In addition, within this survey, coals to be utilized in this program were
identified.
57
-------
Specific objectives were
1. To locate sources of processed smokeless fuel and
to recommend those most suitable for use in the
experimental emissions tests
2. To identify and select one or more natural smokeless
fuels for test and comparison
3. To select one or more other solid fuels, of dissimilar
characteristics to represent fuels not considered
smokeless.
SCOPE AND LIMITATIONS OF COAL SELECTION
The selection of coals were limited to one type from each of the
following classes:
• Processed smokeless fuel
• Anthracite
• Low volatile bituminous coal
• High volatile caking bituminous coal
• Western noncaking bituminous coal.
Practical considerations dictated the following limitations. The
geographical source of each fuel should represent a substantial availability
for domestic and commercial use of the type represented. Shipping distance
and shipping facilities should be chosen to minimize cost of transporting
the test fuel to Battelle. All fuels should be obtained in a size range
appropriate for stokers, avoiding if possible the requirements for preparing
a test fuel by hand methods at Battelle. The processed smokeless fuel should
be obtained from a commercially operated process. These limitations were
accommodated in the final selection of test fuels, as reported in detail later.
TECHNOLOGY OF PROCESSED SMOKELESS FUELS
SMOKELESS COMBUSTION
Smoke is a suspension of small solid particles in flue gases dis-
charged during the burning of fuel. The particles are of two types—
unburned residues of carbon formed by decomposed volatile material from the
fuel, and ash remaining after the fuel is burned.
58
-------
Any fuel may be burned smokelessly at suitable temperatures with
enough oxygen, good mixing, and sufficient time to complete the combustion.
It is important to burn the volatile matter completely before the temperature
rises too.high, because the carbon smoke particles formed by decomposition
without oxygen are difficult to burn, and usually are lost as smoke.
A high volatile coal can give off as much as 40 percent of its
weight as combustible vapors and gases when it is heated. These volatile
gases burn rapidly compared to the carbon and require both a high rate of
air supply and turbulent mixing to permit complete combustion. Even with
sufficient air and complete mixing, conditions can exist in which the
temperature is too low to ignite the entire combustible mixture. For
example, the coal may be added to a cool fuel bed where there is no hot
spot to ignite the tars and gases as they slowly distill. In another,
the vapors and air may be adequately mixed at a sufficient temperature,
but they may pass out of the combustion volume and be quenched by the cool
surfaces in .the boiler and flue. Any of these deficiencies result in
carbon particles and condensed tar droplets that appear as smoke.
Coals with a volatile content of up to 25 percent by weight will
burn smokelessly on beds when a few precautions are taken to provide the
necessary temperature, turbulence, and time in the combustion zone. This
tendency for smokeless combustion follows from the requirements for less
combustion air to burn the volatiles, allowing more air to be available to
burn the solid carbon in the fuel bed (which produces a hotter bed).
Also, less mixing and time are required for complete combustion in the gas
phase above the solid fuel bed than in the fuel bed.
NATURAL SMOKELESS FUELS
Natural smokeless fuels are found in all ranges of volatility.
Anthracite with volatile content of only 2 to 10 percent burns smokelessly,
but must be burned in combustion equipment designed for fuels with low
volatile content. Low volatile smokeless fuels are commonly considered to
be in the range of 12 to 22 percent volatile matter; these fuels can be
burned with almost no smoke in conventional stokers. Moderate precautions
must be taken for fuels with volatile contents in the range of 23 to 25
percent to achieve smokeless burning. (Processed smokeless fuels are
usually supplied with about 8 to 15 percent volatile matter.)
The Pocahontas Seam of low volatile bituminous provides the true
Pocahontas smokeless coal with about 18 percent volatile matter and also
a "semi" Pocahontas from the same seam that has about 23 percent volatile
matter.
PROCESSED SMOKELESS FUELS
Processed smokeless fuels were first prepared and marketed
primarily as a convenience fuel for domestic use on open grates and in
space heaters. The cost of processing was partially covered in some
processes by briquetting fine coal that could not otherwise be used
profitably. The convenience with which the processed fuel could be stored
and burned always justified some price difference above natural fuels, but
59
-------
this price differential in turn limited market growth until antipollution
laws in the 1950's required their use of smokeless fuel. The largest
markets for processed smokeless fuels developed in England and France,
although many processes were studied in other countries without reaching
commercialization.
Europeans developed a variety of smokeless fuels to satisfy the
demands and preferences of consumers who used mostly hand-fired devices for
comfort heating. These devices were relatively simple, because the Europeans
conservatively minimized equipment cost by using open fireplaces and space
heaters in their homes and establishments. The British retained a strong
desire for an open flame as an aesthetic part of the heating device; this
dictated the continued use of the open grate with only slight changes. In
general, the open grate could not be designed to burn coal smokelessly
except as processed smokeless fuels. Regional fuel restrictions required
that only smokeless fuels be used in densely populated areas, so that
captive markets developed.
Space heaters with glass panels in the front doors were later
developed to permit a view of burning fuel. These were favorably received
because they operate more efficiently and have a better natural draft to
burn fuels of lower reactivity than are suitable for an open grate. These
space heaters will not necessarily operate smokelessly, except with processed
fuels. The requirements for smokeless fuels in the metropolitan regions
remain in effect.
The United States did not develop corresponding increased markets
for processed smokeless fuels for two reasons. First, natural gas became
progressively available as pipelines were extended. It was sold at lower
cost than solid fuel. Gas-burning equipment also reached the ultimate of
automatic convenience, that demanded no attention by the householder.
Second, such development as occurred briefly in smokeless solid fuel uses,
before natural gas was available everywhere, reflected basic differences
between fuel markets in the United States and Europe.
Although many hand-fired coal units remained in service into the
1950's, Americans required central heating with automatic operation.
Automatic coal firing was accomplished by a variety of stokers firing into
warm air furnaces or boilers. Stokers were available and that could be
adjusted to fire most of the regional coals efficiently and with minimum
smoke. Thus, with the lack of stringent smoke ordinances, there was no
need to develop a variety of smokeless fuels, since the appliances
automatically maintained a fire in the furnace with occasional attention
to refill the coal hopper. As a result, only two processes for smokeless
fuels reached commercial production in the U.S. because of special situations.
Their characteristic features provide a useful guide to smokeless fuel
potentials in the United States today, as discussed in a following section.
60
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CHARACTERISTICS DESIRED IN SMOKELESS FUELS
The characteristics of the various smokeless fuels, plus their
significance in hand firing and in possible use in stokers in the United
States are background for descriptions in subsequent sections of the
processes used for manufacturing smokeless fuels.
Volatile Matter
The volatile matter in processed smokeless fuels is commonly
about 15 percent which is in the range where smoke is not likely to be
formed under almost any fuel-bed combustion condition. This amount of
volatile is sufficient to permit easy ignition and maintenance of a stable
fire in hand-fired units.
Ash
The ash content has secondary effects in the burning of smokeless
fuel. An ash with low-fusion temperature may form clinkers in the fuel bed.
Such clinkers cause poor air distribution through the grates and are diffi-
cult to discharge even if the grates are properly designed. High ash
fusion temperature gives a powdery ash that can be allowed to build up in
a layer to protect the grates from the hottest parts of the fire, and can
be discharged easily by periodic shaking. However, almost any type of ash
can be accommodated by skillful firing and/or equipment design. In coal
regions with low ash fusion temperature, stokers were commonly designed
to cause fusing,.of the ash into a ring at the bottom of the retort. The
ring was removed once or twice daily in several large pieces with hand tongs.
This was done at the same time the stoker hopper was refilled, and was re-
garded as not particularly difficult for the unskilled operator:
The amount of ash in any fuel depends upon ash content of the
original coal, and the process used in pretreating it for smokeless operation.
High ash content is a disadvantage to the consumer because of the larger
amount of ash that must be dispersed.
Moisture
Processed smokeless fuels usually contain only small amounts of
moisture when originally prepared because most processes require heating
to remove a part of the natural volatile matter. Also, natural smokeless
coals normally have only moderate amounts of moisture. Smokeless fuels
prepared by briquetting of fines may contain large amounts of moisture after
exposure to wet weather, if the binder used in briquetting does not impact
water resistance to the product. This does not impair smokeless combustion
of the fuel but is a disadvantage to the consumer because the fuel is pur-
chased by weight.
Size
The size for domestic stokers is usually a double-screened fuel
about 1-1/4 x 5/8 in. (32 x 16 mm). Top size is determined by the clearance
61
-------
in the feed screw which is not much more than 1 inch. Some undersized fines
are unavoidably formed during crushing, screening, and shipping. An undersize
content of not over 15 percent is acceptable and may be beneficial in uniform
feeding by the screw. An excess amount of fines may interfere with fuel bed
air distribution.
The burning characteristics of anthracite differs from bituminous
coal or processed smokeless fuel, and requires a different design of stoker
with a wider, more shallow fuel bed. The size specified is about 9/16 x 5/16 in.
(14 x 8 mm) for proper combustion in this type of bed.
Hand-fired smokeless fuels used in Great Britain are usually some-
what larger in top size, about 1-5/8 x 3/4 in. (40 x 19 mm), to give a more
open fuel bed for better air flow without forced draft. Briquettes prepared
as a smokeless fuel are usually about 1-1/2 to 2 in. (38 x 50 mm) in the
largest dimension, either egg-shaped or pillow-shaped. Similar briquettes
of processed smokeless fuel were obtained in the United States for these stoker
tests; they are crushed and screened to stoker size.
Bulk Density
Processed smokeless fuels prepared by heating natural coal to drive
off excess volatile matter contains many pores induced by swelling and
release of the volatile matter, and their bulk density in size ranges for
hand and stoker firing is usually about 440 kg/m^ (26 Ib/f t-^) . Smokeless
processed fuels that are prepared by briquetting fine sizes with a binder
and then curing are about twice as dense. For the more dense fuels, a larger
supply of fuel can be stored in the stoker hopper, or in the hand-fired fuel
bed, thus requiring less frequent operator attention.
Strength
The strength of the processed smokeless fuel must be great enough
to prevent excessive formation of fines during shipping and handling. Usually
the low density chars from devolatilized coals tend to be somewhat friable,
according to experience in England (14).
Adequate strength in a processed smokeless fuel may be more important
in stoker firing than for hand firing, because the stoker screw applies more
mechanical stress during the feeding of fuel from the hopper and pushing it
into the retort. Mechanical strength of processed fuel can probably be
adequately controlled by select process conditons. In addition, the coal
must not be so hard and abrasive that the feeding of it causes excessive
wear of the stoker screw.
Caking Properties and Swelling
Essentially all natural and processed smokeless fuels burn without
excessive caking in the fuel bed (caking interferes with distribution of
combustion air). Some of the strongly caking coals have been difficult to
burn in domestic stokers because of formation of "coke trees" pushed up from
the surface of the stoker retort. Although the strongly caking coals could
be burned essentially without smoke, it may be necessary to break up the coke
formations by manually probing the fuel bed.
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Reactivity
Specifications for minimum reactivity of smokeless fuel have been
directed towards minimizing attention and extending the attention interval
in manually fired appliances. In particular, the ignitability of the fuel,
and the recovery of an active fuel bed from a dormant fire have determined
the preference for volatile matter in the processed fuel at levels exceeding
10 percent. The wide range of reactivity and ignitability permissible for
stoker operation indicates that the development of smokeless fuels in the
United States may be influenced more by process economics than by reactivity
requirements.
SMOKELESS FUEL PROCESSES IN THE UNITED STATES
The Disco Process
In the 1930's and 40's, Disco low temperature coke was produced in
a commercial plant by the Consolidation Coal Company to upgrade the fines
recovered from a mine mouth coal-cleaning plant near Pittsburgh, Pennsy-
lvania (B-2, B-3). The strongly caking Pittsburgh seam coal was modified by
preoxidation of the fine feed with air at about 600 F (320 C) to reduce the
plastic properties to a level that would form a sized product of carbonized
balls by agglomeration in the Disco retort. This retort was an inclined
rotating steel cylinder which was externally heated to maintain a temperature
of about 1000 F (540 C) in the heating zone. As the fines followed a spiral
path through the retort, mixing and cascading of the semiplastic charge
resulted in agglomeration of individual particles into ball shapes that
ranged from 1 to 6 in. (25 x 150 mm) in diameter. Commonly, size could be
controlled more closely to a range of 1-1/2 to 3 or 4 inches (38 to 75 or
100 mm). At the exit of the retort the agglomerated product was screened
from the residual fine low temperature char, cooled, and marketed as a pre-
mium fuel for residential heating. Fines were recycled by blending with feed
to the retort.
The plant was closed in the late 40's, presumably because it was
no longer profitable. Residential markets were declining, and cleaning
plant fines could be used to prepare pulverized coal which was in demand for
firing industrial and utility-steam boilers.
Low-Temperature Lignite Carbonization Process
A carbonization plant has been operating in Dickinson, North
Dakota since 1928 to prepare a low-temperature smokeless lignite char.
Lignite from the local strip mine is crushed and processed in two Lurgi
carbonizers of conventional design (17) . The crushed lignite is fed into
a drying section, which is the topmost of three vertically superimposed
sections of the carbonizer shaft. Drying gas circulates through the drying
section, countercurrent to the slowly downward moving lignite. Standpipes
at the bottom discharge the dried material into the middle carbonizing section.
The drying gas maintains the drying section at about 500 F (260 C).
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The carbonizing section is where a portion of the volatile matter
is driven off. It operates at about 1100 F (590 C). These gases and
volatile products are fed to a by-product treatment auxiliary system. Some
by-product gas from the carbonization is burned in a combustor; the hot
combustion products (at about 1100 F) (590 C) are used to heat the carbonizing
section. The carbonized lignite is discharged through reciprocating grates
at the bottom of the carbonization section. The grates control the downward
flow of fuel through both drier and carbonizer. The grates discharge the fuel
into the cooling section where the product is cooled by circulating cool gas
and then discharged to a conveyor or pit for removal to storage. The fine
char is ground and briquetted for sale.
This commercial operation has changed products as the markets
demanded. Initially, the briquettes were prepared with a pitch binder
derived from the process, and were cured by moderate heating and partial
oxidation to give a hard long-burning smokeless fuel approximately equivalent
to anthracite. Domestic heating by solid fuels continued in this area longer
than in other parts of the country, because of the distance from the producing
natural gas fields and the relatively small market offered by the scattered
towns and small population. Coincident with the decline in the domestic
market, the popularity of outdoor cooking and camping increased, so that
there was a growing demand for briquettes suitably modified for grills and
fireplaces. Recently, the shortages of oil and natural gas have suggested
a potential market for fuel briquettes for space heaters. Lignite char
briquettes are distributed widely as a replacement for wood charcoal and
charcoal briquettes that are in short supply.
The modified briquettes are prepared with different binders and
slightly different formulation, depending on the end use. Starch or corn
flour binder has replaced pitch, because the flour is smokeless after drying
at a lower temperature than is necessary for pitch binder. Domestic fuel
briquettes made by this procedure are hard and burn reasonably long, but
not quite so long as the pitch-bound briquettes. The formulation for
outdoor grills and barbecues includes sawdust added to the char before
briquetting, which gives a faster burning, hotter fire appropriate for
cooking. The pitch-treating line is still used occasionally for making and
curing batches of pitch briquettes to be sold on the local market. These
use the substandard char obtained at the end of a continuous run with the
Lurgi carbonizers as the carbonizers are being emptied.
TOSCOAL Process
The TOSCOAL process (18) has been operated in a 25-tpd pilot
plant for retorting of Wyoming subbituminous coal to produce liquid and gas
products, and a smokeless char. The raw coal feed is crushed to -3/4 in.
(19 mm) and preheated by hot flue gas exhausted from a ceramic ball heater
fired with process gas and air. The hot ceramic balls and preheated coal
are introduced together into an inclined rotating pyrolysis drum where
the coal is carbonized by the sensible heat of the balls. The drum
discharges over a screen to separate the char for cooling and the warm
balls for recycle to the ball heater.
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About 80 percent of the heating value of the original coal is
recovered in the char. The volatile matter varies with the temperature of
the carbonizer, and is within the smokeless range of 15 to 25 percent.
The char has been tested as a pulverized boiler fuel. The Hard-
grove grindability is acceptable for pulverizing. Thus, stoker-fuel
briquettes could be manufactured from ground char. Since the process is
set up to recover tar for liquid fuel use, it would probably be preferred
to use a solid binder, such as corn flour, to prepare a solid stoker fuel.
COED Process
The COED process (19) has been studied in a pilot plant with a
capacity of 36 metric tons of coal per day in which over 10,000 metric tons
of coal have been treated. It can handle an agglomerating coal without
pretreatment. Several fluidized beds in series devolatilize the coal without
agglomeration and collect oil and gas as primary products. The beds
successively dry the crushed coal and then devolatilize it at several
increasing temperature levels just below the agglomeration temperature
(which increases as volatile is removed) to produce a char. In the final
bed, part of the char reacts with oxygen and steam to make a hot fluidizing
gas that fluidizes and supplies carbonization heat to the other beds, and
finally is discharged as the gas product. About 60 percent of the heating
value of the raw feed is obtained as a 5 percent volatile char product from
the devolatization steps. Part of the char stream might be diverted from
the inlet of the final gasifying bed, and should be a suitable smokeless
fuel with a volatile content of 12 to 15 percent.
The small size of the fluidized particles would require that the
smokeless char be ground and briquetted with a binder for domestic and
commercial stoker use. This option has not been studied as a part of the
pilot plant development work.
SMOKELESS FUEL PROCESSES IN ENGLAND
A survey of the quality and characteristics of smokeless fuels
readily available to domestic consumers in England covered seven processed
fuels and anthracite (14). The following summaries indicate brand names
and properties of these fuels.
Process Features and Fuel Characteristics
Anthracite—
This natural smokeless fuel is double screened to provide size
ranges suitable for hand firing. There are four grades of anthracite
marketed, representing two ranges of volatile content, above and below
6.5 percent, and two ranges of ash content, above and below 3 percent ash.
Phurnacite—
This is made by briquetting fine sizes of low volatile fuels.
It is similar to natural anthracite: low volatile content, high density,
igniting with difficulty in a hand-fired appliance. Briquettes of this
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type are prepared from fine sizes of fuel from many sources and are widely
available.
Presumably, similar briquettes could be made from the low volatile
char produced in the final combustion stage of the COED process. These could
be used in domestic stokers, because difficulty with ignition would not be
a problem in automatic equipment.
Gas Coke or GLOCO—
Gas coke is a residue from the manufacture of coal gas for city
distribution in England. GLOCO is a brand name for gas coke. There is no
equivalent product in the United States, because coal gas as a domestic fuel
has been entirely replaced by natural gas. Gas coke is a porous, low-
density fuel (340 kg/m3, 21 lb/ft3) of nominal sizes 2 x 1 or 1-1/4 x 1/2 inch
(50 x 25 or 32 x 12 mm). Because it is friable, there is likely to be con-
siderable undersize material produced in shipping and handling.
SUNBRITE—
This trade name of the National Coal Board of Great Britain is
applied to small sizes recovered from any hard coke plant. There is no
official specification of properties. Two sizes for domestic use are
nominally 1-1/2 x 1 inch (38 x 25 mm) and 1 inch x 1/2 inch (25 x 12 mm).
Hard coke of similar properties is recovered from coke ovens in the
United States. Low volatility makes it a difficult fuel to hand fire in a
domestic appliance in England, and the physical properties of high strength
and abrasiveness would make it generally unsuitable for domestic stoker
firing in the United States.
REXCO, COALITE, or WARMCO—These are low temperature cokes with
similar properties. REXCO and COALITE are the products of private manu-
facturers, and WARMCO is marketed by the National Coal Board. Properties of
the products reflect the quality and type of coal processed and the tempera-
ture of carbonization. REXCO is made in a number of different plants of the
National Carbonizing Company throughout Egland. This brand of low-temperature
coke was reported by the company to have a volatile content of about 7.6
percent. The fuel appeared to be fragile, with undersize excessive in many
samples. Ignition performance was reportedly not good for any of these brands
for manually tended open fires. The ignition would not be a problem in stoker
firing, but undersize and friability presumably would make satisfactory control
of a stoker fire difficult. Briquettes of the proper size for stoker firing,
with smokeless binder properly cured after briquetting, would be acceptable
in small automatic stokers.
PROCESS AND EQUIPMENT FOR REXCO SMOKELESS FUEL
The low temperature carbonization retort that produces REXCO fuel
has undergone a long series of developments and improvements since the 1930's,
and is discussed here as typical of a process that might be used in the
United States to satisfy demands for processed smokeless fuel. All low
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temperature coke processes use internal heating by recirculating the combus-
tion products from fuel gas evolved during the carbonization (20). The
original retorts were 10 feet (3.05 mm) in diameter and the process was inter-
mittent, with repeated cycles of charging, carbonizing, and discharging the
carbonized product. When the Clean Air Act was passed in England in 1956,
demand increased and improved retorts were built along the same basic design
as the original ones. The earlier improvements retained intermittent opera-
tions of the retort, but the refractory lining was reduced in thickness to
increase capacity, and methods of handling the dondensate from the off gas
were refined to reduce atmospheric pollution. All the burnable gas produced
is used in the process, for carbonizing and for heat in the by-product
refining steps.
The most recent improvement was an entirely new plant with
continuous retorts, incorporating materials handling equipment, centralized
automatic controls, auxiliary systems for recovering condensed tars and
aqueous liquors as by-products, gas burners for heating the charge, product
fuel quenching, classification, and bunker storage (21).
The REXCO plant is at the mine mouth of the Snibston Colliery,
which supplies coal directly by conveyor from the coal washing plant. There
are five identical continuous retorts, each with its own complete combustion
system and gas treatment, plus hydraulically operated control units. The
capacity of each retort is 200 metric tons of coal per day or 1000 metric
tons per day total for the plant. Yield is about 75 percent so that the
annual production of smokeless REXCO fuel by low temperature carbonization
at this plant is more than 250,000 metric tons per year. The plant was
operating at full capacity in 1974. The National Carbonizing Company has
three older plants also operating, so that the total capacity for REXCO fuel
of all grades is about 900,000 metric tons per year (22). It also has been
reported that the REXCO continuous process would be used to carbonize raw
briquettes to produce smokeless Phurnacite (23).
SELECTED FEATURES OF OTHER
SMOKELESS FUEL PROCESSES
Fluidized-Bed Low-Temperature Carbonization
Fluidized beds for partial devolatilization of coal fines to
produce a low-temperature coke have advantages characteristic of all fluidized
beds in that (1) a uniform temperature is maintained and controlled throughout
the bed volume, (2) rapid heat transfer is attained between fluidizing gas
and solid particles for either heating or cooling, and (3) that the solids
are easily handled into and out of the bed because they will flow like a
liquid when properly fluidized. Continuous withdrawal of the product at
carbonization temperature is several pilot-plant tests has permitted bri-
quetting of the hot char while it is still semiplastic without the necessity
for using an added binder or for reheating in the briquetting process.
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Substantial pilot-plant operations and commercial-scale experimental runs were
carried out in the 1960's.
No substantial commercial production of smokeless fuels in fluidized-
bed carbonizers is known at the present time. Presumably the advantages of
fluidized beds cited above are counterbalanced by the known disadvantages of
excessive carryover that may be induced by size degradation of a friable solid,
such as low-temperature coke, during fluidization.
Methods for Curing Briquettes
Briquettes with a pitch binder should be cured to insure smokeless
combustion in hand firing, and to improve the mechanical properties of
strength, water resistance, and resistance to temperature shock and crumbling
in the fuel bed.
Mild heat treatment in the presence of a gas containing several
percent oxygen at a temperature of about 660 F (350 C) produces a stable
briquette by oxidation of the briquette surface and polymerization of the
pitch binder with substantial increase in its softening temperature.
Commercial processes in the Netherlands and France have used a number of
variations. Some plants have multiple intermittently charged curing reactors
for treating briquettes for about an hour with flue gases containing about
50 percent air. A continuous curing process employed a traveling grate with
the oxygenated flue gas forced upward through the bars.
In the preceding section it was noted that a modified REXCO continuous
carbonizer was scheduled for operation in curing briquettes under similar
conditions.
A fludized-bed briquette-curing process developed in France by the
National Institute of the Carbonization Industry (INICHAR) (B24) uses a
fludized bed of sand particles in which the green briquettes are immersed
while the treatment mixture flows continuously from the inlet to the exit
of a fludizing trough. The sand is preheated to about 400 C and the cold
briquettes are added to the fluidized briquette preheating zone where they
are raised to a temperature of over 300 C before they flow continuously
over a weir with some sand into the curing zone. In the curing zone they
pass over multiple hot gas inlets that maintain fluidization of the sand-
briquette mixture. Because of reaction with the oxygen in the fluidizing
gas the temperature slowly rises until they are discharged at about 360 C
over the exit weir. They travel over an inclined screen that separates
and recycles the sand and fines before the cured briquettes are discharged
onto a cooling conveyor to storage.
Because it is probable that stoker-sized smokeless processed fuel
must be agglomerated or pelletized by some method, these various procedures
for curing briquettes are of interest when considering the potential use of
smokeless processed fuel for stokers. The pellets (small briquettes) must
be cured in some manner to provide adequate mechanical resistance to de-
gradation in the stoker screw and sufficient heat resistance so that they
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do not spall or disintegrate in the stoker fuel bed. Lack of heat resistance
has been a problem in many pelletizing and briquetting operations that use
smokeless binders, such as those used in the lignite-char briquettes described
in the section on United States processes.
SOURCES OF TEST FUELS
The guidelines for selecting specific sources of the five typical
fuels for the test program were described early under Scope and Limitations.
This section presents a description of the fuels selected and procured for
stoker emission tests. The basis for selection and some of the alternatives
considered are described.
Processed Smokeless Fuel
Lignite char briquettes were purchased from Husky Industries of
Dickenson, North Dakota. This was the only acceptable U.S. source of
processed smokeless fuel from a commercial process.
Other sources considered were from the pilot plant processes
described previously. TOSCOAL was not available in sufficient quantity
for the test, and would have had to be obtained by a custom run of the pilot
plant for one day with production of at least 25 tons of char from Western
coal. This char would have had to been pelletized or briquetted in another
custom operation. No effort was made to locate a source for briquetting.
COED char was not available because the pilot plant is not now in
operation, awaiting the possibility of the renewal of the government operating
contract. Even if obtainable, the processed COED char would also have had to
be briquetted in a custom operation.
The possibility was considered of using briquettes from an inter-
mediate stage of the manufacture of formed coke by a proprietary process of
the FMC Corporation. The briquets are made from a Western coal char that is
ground after low temperature carbonization, briquetted with a proprietary
binder, cured, and then carbonized to a low volatile content for metallurgical
use. It seemed possible that the cured briquettes would have volatile content
in the preferred range before the carbonization step. We were advised that
they should not be used, as they were not typical or suitable for a domestic
stoker fuel.
Importing a processed smokeless fuel from England was ruled out
on several considerations. The cost including packaging and shipment to
Battelle-Columbus was prohibitive at an estimated $700 per metric ton. The
product was not necessarily typical of any processed fuel made from American
coal. None of the processed fuels in England are intended for stoker firing
and probably would not be suitable.
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Anthracite
There were no retail sources for anthracite in the Columbus area.
Accordingly, an experimental lot of Number 1 Buckwheat Pennsylvania anthra-
cite in 50 pound bags was obtained from the mine operated by Beltrami Enter-
prises, Inc., through the GA Fuel Sales, Division of Blue Coal Corporation,
P.O. Box 568, Wilkes-Barre, Pennsylvania 19703.
Low Volatile Bituminous Coal
A search for sources of low volatile bituminous coal determined that
most of the low volatile from the Pocahontas seam is preempted for blending
with other coals to make metallurgical coke. It is shipped to the coke ovens
as mine run sizes. Through the assistance of many persons in the Consolidation
Coal Company, a shipment of low volatile bituminous coal (Pocahontas Number 3
seam) was procured from the Bishop mine at Bishop, Virginia.
High Volatile Caking Bituminous Coal
A stoker coal of this classification was available locally in the
Columbus area and was marketed by the South East Coal Sales Company of
Columbus. The coal procured was an Eastern Kentucky coal mined by the South-
east Coal Company, Irvine, Kentucky, at their Polly mine from the Upper Elkhorn
Number 3 seam. The Elkhorn Number 3 seam is a high volatile B bituminous coal.
Western Noncaking Bituminous Coal
Several mines listed in the 1973 Keystone Coal Industry Manual
(25) as producers of stoker size Western coal were selected for consideration.
Alternate coals from Kansas and Wyoming were also considered. The Kansas coal
appeared unsuitable because it was from the Western Region of the Interior
Province, and was not regarded as a typical Western coal.
A Wyoming coal from the Elkol mine of the Kemmerrer Coal Company in
Lincoln County, Wyoming, was considered. This is a subbituminous B coal from
an Adaville seam, of which there are several. The composite analysis of
the adaville seams is - moisture, 21 percent; ash, 3.6 percent; sulfur, 0.6
percent; heating value, 9700 Btu per pound. This coal is lower rank with
higher moisture and presumably would be somewhat more reactive than the Colorado
coal if it were made into a char and briquetted. However, the test lot of
processed and briquetted lignite char is also an example of high moisture, low
rank fuel of high reactivity and the Colorado coal appeared to be a better choice
for achieving a range of characteristic properties among the five test lots.
The final selection was the Corley strip mine in Fremont County,
Colorado, which prepares an air-cleaned stoker coal. This coal was mined
from the Black Diamond seam.
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ENVIRONMENTAL CONSIDERATIONS
The use in stokers of smokeless fuel prepared by low-temperature
carbonization of coals from various areas requires consideration of environ-
mental impacts of emissions from the manufacturing plant and from the stokers
as well.
STOKER EMISSIONS FROM PROCESSED COAL
It is anticipated that particulate and POM emissions from firing
a processed smokeless fuel in stokers would be less than those from firing
a high volatile bituminous coal. This expected result is based upon the
particulate and smoke emissions of stokers firing low volatile coal that are
generally lower than high volatile coals. There are no data available as to
the performance of a stoker firing this fuel.
One potential problem that will be considered from firing a pro-
cessed smokeless fuel is the possible loss of ignition during the "holdfire"
period. During seasonal changes, stokers often run only 5 minutes during a
30-minute cycle. With the low volatile content of the smokeless fuel, the
raw coal fed into the retort may not ignite properly and burn uniformly because
of the low-bed temperatures. It may be necessary to operate the stoker for
longer than 5 minutes every cycle to maintain a suitable fuel bed to ignite
the raw coal.
FUEL-PROCESSING PLANT EMISSIONS
All smokeless-fuel processing plants in the United States will be
new. An appraisal of the overall significance of plant emissions from these
sources must depend on estimates of prcesses to be used, size and location
of individual plants, and the rate at which they are constructed to satisfy
market demands. A projection of the qualitative course of such developments
is presented in the next section, but formal environmental impact assessments
with quantitative treatment of individual plant emissions is not justified
here, in the absence of a more definitive data base.
As a useful alternative, the literature study of processing methods
provided background information for a qualitative summary of pollution sources
from a processing plant. Process operations identified in the literature
study indicate that the pollution potential and the emission of pollutants
is similar to those from an oven (metallurgical) coke plant. The older
designs of coke plants used intermittent charging of coal and intermittent
discharge by pushing the hot coke into an open-top receiver and quenching
with water. By-product coke ovens condensed the volatile matter given off
during coking as tar and aqueous ammoniacal liquor. Uncondensed gas was
scrubbed and purified before use as fuel in the process or for sale. Much
of the pollution from coke ovens was from pushing and quenching the coke in
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open air, and from the release of particulates when a coal charge was dumped
into the oven.
Conventional low-temperature carbonization processes similarly
operate intermittently. They differ from coke ovens in heating the charge
internally by the combustion products from process gas, instead of through
the oven walls as in coke oven. Light oils are produced in greater quantities
than the high temperature tar. The more volatile oils require somewhat more
efficient gas-scrubbing apparatus for equivalent purification of the gas.
There is no important difference in pollution potential, because the gas
for process heat is burned to nonpolluting combustion products in the heating
furnaces of both processes.
Considerable recent information is available in the engineering
literature on the improvement of coke into closed containers for quenching.
This literature was not covered as part of the smokeless fuel survey, but
would be available for detailed background information if it were necessary
to prepare a formal environmental impact assessment for a planned low tempera-
ture carbonization plant. Operational details would also be available from
the low temperature carbonization plant at the Snibston Colliery in England
(B-5), if a specific site for a United States plant were being considered.
For the qualitative requirements of this survey, it is useful to
list the following features at Snibston that are claimed to virtually
eliminate pollution sources.
• The plant is located on 40 acres adjacent to a mine
which normally supplies all requirements for raw coal
feed. Transportation with loading and unloading of
coal by conventional means is eliminated. A conveyor
supplies coal directly from the mine preparation plant
to a storage bunker.
• The storage bunkers are filled separately with various
sizes of coal from the mine screening plants and blends
for use in the process are automatically delivered to
a continuous conveyor.
• The blend is passed through a final screening to remove
fines and then proceeds by conveyor to each of the five
continuous retorts.
• Each retort operates independently with its own gas
scrubbers, combustion chambers, condensers and
hydraulic units, so that a shutdown or beginning of a
campaign does not overload or disrupt the operation
of the other independent systems, with accompanying
possibility of overflows or bypassing of materials
in process.
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• Each retort discharges its smokeless fuel into a water
seal, which quenches the charge and is the underwater
inlet for a drag conveyor feeding the storage bunkers.
This method of discharge and disposal minimizes dust
and odor from the quenching and handling process.
• A waste gas incinerator burns or decomposes traces of
pollutants in the aqueous liquor and the waste gas so
that noxious materials are burned before discharge.
• The central control panel at the plant registers and
controls the coal feed, conveyor handling, and the
operation of the retorts. Thus, the probability of
malfunctions is reduced, and precise control insures
that operations are maintained for minimum pollution
as well as maximum production.
An additional operation that has pollution potential is the curing
of briquettes. It has been noted above (20) that the REXCO continuous retort
also was planned for use to carbonize smokeless briquettes, with equal potential
for reducing possible emissions from the briquette carbonizing process.
The fluidized hot-sand cure for briquettes (21) was reported to
be an efficient procedure because of improved temperature and time control
during processing, and no weight change. The cure should produce little
pollution from the effluents. The volatile loss is less, than 2 percent during
the curing operation because of the precise temperature control. Low tempera-
ture oxidation hardens the briquette surface, with retention of about 2 per-
cent by weight of oxygen to balance the small volatile loss.
EVALUATION AND INTERPRETATION
OF THE SMOKELESS COAL SURVEY
ANALYSIS OF SMOKELESS COAL
Smokeless coal is defined as having less than 25 percent volatile
matter. It is believed that many higher volatile coals can be burned smoke-
lessly in a properly designed and adjusted stoker. This conclusion was
verified in experimental studies for the Eastern and Western high volatile
coal.
SUITABILITY
The suitable process for manufacturing smokeless coal is one that
uses low-temperature carbonization of the high volatile raw coal followed
by further processing to produce a fuel of acceptable characteristics for
feeding and combustion in a stoker. These characteristics include adequate
mechanical strength, thermal resistance to spalling in the stoker fuel bed,
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and low abrasiveness within the capabilities of the stoker screw to handle
without excessive wear. The process probably must include a briquetting
or pelletizing step with curing of the briquettes (pellets) for adequate
strength.
Oven coke breeze could be burned in a stoker but would be too
abrasive. Low-temperature char is probably too friable for use in a stoker.
ENVIRONMENTAL IMPACT
Stokers can be adjusted to burn solid fuels smokelessly. All of
the organic sulfur and much of the pyritic sulfur in the coal will appear
as sulfur dioxide in the flue gases from the stoker-fired furnace. POM
emissions will also be present. Although these are tarry materials, con-
centrations of possible environmental interest may not be visible nor
detectable by odor. Sensitive techniques can be used to identify POM
emissions but the quantitative significance of their environmental impact
at the detectable concentrations has not yet been defined.
The environmental impact of individual smokeless coal process
plants can be controlled by applying known antipollution principles to the
design of new plants. There is only one smokeless fuel plant operating on
a commercial scale in the United States. It is in full production to
supply domestic hand-fired markets so that new stoker markets will have to
be supplied predominantly by newly designed plants with the necessary anti-
pollution safeguards.
LONG- AND SHORT-TERM AVAILABILITY
There is no production of processed smokeless coal for stoker use
at the present time. Short-term availability must depend upon natural smoke-
less fuels. Low-volatile smokeless bituminous coals are in short supply
for metallurgical uses. The supply of anthracite would be adequate to supply
anthracite burning stokers. This supply could be expanded with reasonable
speed as fast as anthracite stokers could be manufactured and installed for
its use. If high volatile coal can be included in the smokeless category
when burned in modified stokers, then short-term availability is subject
only to the general problems of supplying coal to meet increasing demands
of the total market. If a smokeless coal is also defined as one with
suitably low sulfur emissions, the problems of short-term availability
will be the same as for any other use that limits sulfur content in the
effluent.
The long-term availability of smokeless coal depends on the growth
of a profitable market. If processed smokeless fuel must be manufactured,
processing plants must first be built. Their availability will depend on
advanced planning with possible subsidies or favorable profit prospects
in the economics of processing coal to produce a product with an acceptable
smokeless composition.
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ECONOMICS
The economics of smokeless solid fuel production and marketing
depends on the following influences which are not well defined. The unit
cost of the heat energy developed from a processed smokeless coal by burning
it in a stoker will be higher than unprocessed coal, because the process is
less than 100 percent efficient, and the capital and operating costs must be
covered as well. Past experience with low-temperature carbonization has
shown that by-product credits were no higher than the equivalent fuel value
of the recovered tar. A review of the possibility that by-product credits
may be increased by the current shortage of liquid petroleum products is
beyond the scope of this study.
A subjective judgment derived from this smokeless fuel survey is
that the economics of smokeless fuel processes may be unfavorable if com-
pared with development of improved designs of domestic and commercial
stokers that are adjustable to burn various regional coals really smoke-
lessly. Devolatilization processes to produce conventional smokeless fuels
are not specifically directed toward the use of such fuels in a stoker.
Adapting these fuels for stoker use by briquetting introduces an added
economic penalty.
If sulfur emissions must also be controlled, then the use of a
low-sulfur coal or a process that removes a substantial part of the sulfur
in high-sulfur coals might be required. (Small stokers cannot be designed
at reasonable cost or adjusted to eliminate sulfur in the flue gas.) The
economics of eliminating POM from stoker emissions is unknown until the
extent and character of such emissions is measured.
75
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REFERENCES
1. Sherman, R. A. What Research Tells Us About Stokers and Stoker Coals.
Conference Proceedings, The Cleveland Coal and Stoker Institute, 1940.
pp 81-96.
2. Internal Battelle's Columbus Laboratories Report.
3. Barrett, R. E., et al. Field Investigation of Emissions from Combustion
Equipment for Space Heating. EPA-R2-73-084a, US. Environmental Protection
Agency, Washington, B.C., 1973.
4. Jones, P. W., et al. Efficient Collection of Polycyclic Organic
Compounds From Combustion Effluents. Paper No. 75-33.3 presented at the
68th Annual Meeting of the Air Pollution Control Association, Boston,
1975.
5. Standard Method of Test for Smoke Density in the=Flue Gases From
Distillate Fuels, ASTM Designation: D 2156-65 (reapproved 1970).
6. Committee on Biologic Effects'of Atmospheric Pollutants. Biologic.
Effects of Atmospheric Pollutants;•Particulate Polycyclic Organic '
Matter. National Academy of Sciences, National Research Council,
Washington, D. C., 1972. pp 375.
7. Compilation of Air Pollutant Emission Factors. AP-42, U.S. Environ-
mental Protection Agency, 1973.
8. Giammar, R. D., et al. The Effect of Additives in Reducing Particulate
Emissions From Residual Oil Combustion. ASME Publication 75-WA-CD-7.
11 pp.
9. Hangebrauck, R. P., von Lehmden, D. J., and Meeker, J. E. Sources of
Polynuclear Hydrocarbons in the Atmosphere. HEW, AP No. 999-AP-33,
Durham, NC, 1967.
10. Sherman, Ralph A. Stoker Patent No. 2,371,191, U.S. Patent Office,
March 13, 1945. 5 pp.
11. Compilation of Air Pollutant Emission Factors. U.S. Environmental
Protection Agency, Office of Air Programs Publication No. AP-42,
1973.
12. Oil Heating Users Total 11,186,650. Fueloil & Oil Heat, 44, Jan, 1970.
13. Putnam, A. A., et al. Evaluation of National Boiler Inventory.
Final Report to U.S. Environmental Protection Agency, Contract
No. 68-02-1223, Task 31, 1975.
76
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REFERENCES (continued)
14. Smokeless Fuels. Shopper's Guide, 26:2-13, May, 1962.
15. Solid Smokeless Fuels. United Nations Economic Commission for Europe,
ST/ECE/COAL/22, p 10, United Nations Publications, Sales No. 68.II.E/Mim.
5, 1967.
16. Leisure, C. E. Production of Low Temperature Coke by the Disco
Process. AIME, Tech. Publ. 1176, 1940.
17. Reid, William T. Low Temperature Carbonization of Coal in Japan.
I.C. 7430, U.S. Bureau of Mines, 1948, 82 pp.
18. Carlson, R. B., Yardumian, L. H., Atwood, M. T. TOSCOAL Process for
Low Temperature Pyrolysis of Coal. Soc. Min. Eng., AIME, Transactions,
256:128-131, June, 1974.
19. Jones, J. F. Project COED (Char-Oil-Energy Development): Symposium on
"Clean Fuels from Coal", Illinois Institute of Technology Center,
Institute of Gas Technology, Chicago, September, 1973. pp 383-401.
20. Potter, N. M., and Martindale, J. R. Modern Developments in Smokeless
Fuels. Mining Engineer, December, 1966. pp 195-205.
21. Brighter Prospects at Snibston. Energy Digest, May/June, 1974. pp 2-5.
22. Winton, D. Gas World, 176(4603), Nov 11, 1972. pp 399-401.
23. Fuel Heat Technology J., 16:(3), May, 1969. p 37.
24. Treatment of Carbonaceous Materials in Fluidized Beds. British Patent
Nos. 907,909 and 907,909 (October, 1962); 928,829 and 928,829.
June. 1963.
25. Keystone Coal Industry Manual. McGraw-Hill Publications. New York,
1973.
77
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-76-029
2.
3. RECIPIENT'S ACCESSION-NO.
4. T,TLE AND SUBTITLE Emissions from Residential and Small
Commercial Stoker-Coal-Fired Boilers Under
Smokeless Operation
5. REPORT DATE
October 1976
6. PERFORMING ORGANIZATION CODE
7 AUTHORIS) Robert D. Giammar, Richard B. Engdahl,
and Richard E. Barrett
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Battelie-Columbus Laboratories
505 King Avenue
Columbus, OH 43201
10. PROGRAM ELEMENT NO.
EHE624
11. CONTRACT/GRANT NO.
68-02-1848
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final; 11/74-9/76
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES IERL_RTp project Officer for this report is J. H. Wasser,
919/549-8411 Ext 2476, Mail Drop 65.
16. ABSTRACT ,
The report gives results of a technical assessment of the advisability of
increased use of stoker coal for residential and small commercial space heaters.
The assessment was based on: (1) an experimental laboratory study (major emphasis)
to evaluate emissions from a 20-hp (200 kw) boiler firing anthracite, Western subbi-
tuminous, processed lignite char (smokeless coal), and high and low volatile bitumi-
nous coals (pollutants of major interest were smoke, particulate, and POM); (2) a
survey to identify manufacturers and designs of currently marketed stokers; and (3)
a survey to identify processes for the manufacture of smokeless coals and to evaluate
the suitability of these fuels for stoker firing. The experimental investigation indi-
cated that smokeless operation of a small stoker could be achieved for the coals eval-
uated (coals generating the highest smoke levels generated the highest particulate and
POM levels). Coals with the highest volatile matter and the highest free swelling
index had the highest levels of these emissions. It also indicated that a potential
exists to reduce emissions both by minor modifications in the stoker design and oper-
ation, and by use of processed or treated coals. Even these emission levels would be
considerably higher than those from equivalent oil- and gas-fired systems.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Pollution
Stokers
Coal
Combustion
Boilers
Flue Gases
Space Heaters
Smoke
Polycyclic Com-
pounds
Air Pollution Control
Stationary Sources
Particulate
Residential
Small Commercial
Smokeless Coal
13B
13A
2 ID
2 IB
07C
13. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
84
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
78
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