United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-183/184 Oct. 1981
Project Summary
CoahdRDF Demonstration
Test in an Industrial Spreader
Stoker Boiler. Use of
CoahdRDF Blends in Stoker-
Fired Boilers. Volumes I and II
Matt Stoermer
In one concept involving the recovery
of energy from solid waste, refuse is
combusted either directly for steam
recovery or in combination with fossil
fuels for power generation. The report
summarized here (Phase II or a two-
phased program) considers a demon-
stration test of the co-firing of coal
and a densif ied form of refuse-derived
fuel (d-RDF) in an industrial spreader
stoker boiler in Erie. Pennsylvania. In a
402-hr period, 1.702 tons of d-RDF
were co-fired with coal. An additional
231 hr of coal baseline testing were
completed to provide a basis of
comparison for the test results. Phase
I was conducted with a smaller, insti-
tutional, spreader stoker heating
boiler at Hagerstown, Maryland.
The demonstration tests investigated
(1) the material handling character-
istics of d-RDF; (2) boiler performance,
i.e., boiler efficiency, spreader limita-
tions, steam production, combustion
properties, slagging, fouling, clinker-
ing, and corrosion; (3) environmental
performance, i.e., particulate emis-
sions (size, mass rate, and resistivity,
gaseous emissions (SO*, NO*, Cl, F,
HC), and trace metal emissions (Pb,
Cr, Cd, Be, and Zn).
In general, the test demonstrated
that co-firing coal and d-RDF can be
performed with minimal impact on the
performance of an industrial power
plant. The boiler was able to deliver
maximum rated steam capacity with
adequate boiler response and fuel
burnout at coal:d-RDF blends up to
1:4 (by volume). The slight decrease in
boiler efficiency occurring during
blend firing was attributed to the high
moisture and hydrogen content of the
d-RDF pellets. There was no significant
difference in particulate emissions of
either the electrostatic precipitator
(ESP) inlet or outlet as a result of firing
with blends. ESP collection efficiency
was not effected by the blend firing.
Increases in heavy metals (lead,
cadmium, zinc, chromium) and chlo-
ride emissions were noted. Sulfur
emissions decreased as the d-RDF
substitution was increased.
This Project Summary was devel-
oped by EPA's Municipal Environ-
mental Research Laboratory, Cincin-
nati, OH, to announce key findings of
the research projects that are fully
documented in separate reports (see
Project Reports ordering information
at back).
Introduction
The U.S. Environmental Protection
Agency (EPA) assigned the Municipal
Environmental Research Laboratory
(MERL) in Cincinnati, Ohio, major
responsibility for research and develop-
ment in the field of recovery and use of
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municipal solid waste. One concept
investigated involves the recovery of
energy from solid waste. Refuse is
combusted either directly for steam
recovery or in combination with fossil
fuels for power generation. The latter
involves processing the refuse to
remove the combustibles for use in a
modified power generating boiler, usually
in combination with coal. The processed
refuse is usually referred to as refuse-
derived fuel (RDF).
The RDF concept in the United States
has generally been limited to power
generating facilities that burn pulverized
coal. Use of RDF need not be limited to
large users, however, and may in fact be
more valuable to small power generating
facilities. Small industrial and institu-
tional boiler owners may find RDF an
attractive and cheaper supplement to
fossil fuels, for which they receive no
quantity discounts, as do the large
users. In addition, small users may have
increased flexibility in negotiating
contracts for RDF (especially with
regard to length of commitment). Many
small power generators are economically
marginal because their boiler facilities
are older, coal-burning models that
require costly air pollution equipment.
The use of RDF may help such facilities
absorb the cost for such controls.
RDF prepared for large utility boilers
is typically composed of the light
fraction of shredded refuse that has
been air-classified, screened, or other-
wise processed to remove the noncom-
bustibles. In this fluffy form, it can be
pneumatically fed into the suspension
utility boiler. For the smaller, stoker-fed
boilers, however, a densified form of
RDF (i.e., d-RDF) is used.
,This d-RDF may approximate the
physical characteristics of the stoker
coal fed to the boiler. RDF in this form
offers increased flexibility in transport,
handling, and storage, and it can be
mixed directly with the coal and fed to
the boiler with few if any modifications.
Although considerable experience
was available for co-firing RDF and coal,
little information was available on the
production and burning of d-RDF. EPA
therefore implemented parallel pro-
grams to (1) determine the engineering
and economic aspects of preparing d-
RDF and (2) assess the technical and
environmental implications of using d-
RDF as a coal substitute.
In addition to the report summarized
here, the following reports have been
prepared as part of these programs:
"Densification of Refuse-Derived
Fuels: Preparation, Properties, and
Systems for Small Communities,"
EPA-600/2-81-188,
"Fundamental Consideration for Pre-
paring Densified Refuse-Derived
Fuels," EPA-600/2-81-180, and
"A Field Test Using Coal: d-RDF
Blends in Spreader Stoker-Fired
Boilers," EPA-600/2-80-095.
The results reported herein represent
the second phase of a two-phase d-RDF
combustion evaluation program. Phase
I was conducted in an institutional
spreader stoker heating boiler located in
Hagerstown, Maryland (EPA Report No.
600/2-80-095). During Phase I, 285
tons of d-RDF were combusted. Phase II
demonstration testing was conducted in
a larger, industrial, spreader stoker
boiler operated by General Electric in
Erie, Pennsylvania. In a period of 402
hours, 1,702 tons of d-RDF were
combusted with coal. An additional 231
hours of coal baseline testing was
completed to provide a basis of com-
parison for the test results.
The demonstration tests were de-
signed to investigate (1) the material
handling characteristics of d-RDF after
6 months of storage in an open coal
yard; (2) boiler performance, i.e., boiler
efficiency, spreader limitations, steam
production, combustion properties,
slagging, fouling, clinkering, and cor-
rosion; (3) environmental performance,
i.e., paniculate emissions (size, mass
rate, and resistivity), gaseous emissions
(SOx, N0», Cl, F, HC), and trace metal
emissions (Pb, Cr, Cd, Be, and Zn).
Previous field tests involving co-firing
coal and densified refuse derived fuel
(d-RDF) have typically been of short
duration and were performed under less
than desirable boiler operating con-
ditions and boiler specifications. There-
fore, the objective of this demonstration
test was to conduct longer-term co-
firing tests in a boiler representative of
those used throughout industry. Suf-
ficient testing, with the exception of
long-term corrosion studies, was to be
conducted to establish whether or not d-
RDF (1) has any detrimental effects on
the boiler system or its performance and
(2) if it can be burned within existing
environmental constraints.
Site Selection
After establishing the site selection
criteria, a site was located. A detailed
.discussion of the selection criteria that
were established are included in the
report. The basic criteria for selecting a
test and demonstration site were:
1. that the site have a spreader
stoker boiler with traveling grate
(front ash drop) capable of pro-
ducing 75,000 to 150,000 Ib/hr of
steam at 500 to 1,000 psig with at
least 200°F superheat,
2. that the site have multiple boilers
and sufficient steam capacity to
permit operating the test boiler at
any desired steam load,
3. that the site have adequate fuel
storage capacity, a feeding system,
and other facilities readily adapt-
able to testing requirements, and
4. that the power plant management
be sufficiently interested and
cooperative to ensure successful
completion of the program.
After reviewing approximately 40
candidate sites, the General Electric
Power Plant in Erie, Pennsylvania, was
determined to be the most suitable. This
power plant has three Babcock and
Wilcox* spreader stoker-fired boilers
rated at 100,000,150,000, and 175,000
Ib/hr of steam with 285°F superheat at
675 psig. The 150,000-Ib/hr boiler was
selected for the demonstration test.
Boiler performance was evaluated to
determine boiler efficiency and fireside
corrosion. The flue gas was continuously
monitored at the boiler outlet to provide
necessary data for calculating the
efficiency. The instruments on the
boiler control panel were monitored to
document operational characteristics of
the system.
Fuel
The d-RDF for the demonstration was
produced at two pilot-scale plants.
Commercial sources were not available.
Even with d-RDF supplying less than
half the fuel demand of this industrial
boiler, more than 6 month's production
was needed to accumulate enough d-
RDF for a 400-hr test.
Both d-RDF's were formed as 1/2-
inch-diameter cylindrical pellets. One
pellet type, produced by the National
Center for Resource Recovery (NCRR)
contained approximately 30 percent ash
and had a heating value of 6,755 Btu/lb
on a dry weight basis. The other pellet
type, produced by Teledyne National,
contained 14 percent ash and had a dry
weight heating value of 8,123 Btu/lb.
"Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use.
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Moisture contents of the d-RDF ranged
from 14 to 34 percent, and bulk
densities ranged between 30 and 35
Ib/ft3. The ash content of the d-RDF
produced by NCRR was later reduced
significantly by modifications to the
process. The d-RDF was shipped to Erie,
Pennsylvania, via truck from production
sites in Washington, D.C.,and Baltimore,
Maryland. Some of the NCRR production
had been stored in the open several
months before shipment.
At Erie, the d-RDF was stored up to 6
months in an open coal yard through
winter and spring weather. The piles of
d-RDF formed a protective crust 6 to 8
inches thick. While in storage, the
pellets increased in moisture and fines
content. Also, the aged pellets expanded
and formed serrated edges that sub-
sequently created some handling
problems.
' Five different coals were used during
the blend firing and coal baseline tests.
These coals had sulfur contents ranging
from 1.7 to 6.8 percent and ash contents
ranging from 9.5 to 18.2 percent on a
dry weight basis.
Results
While being conveyed to the bunker,
the d-RDF blended thoroughly with the
coal. The low bulk density, high elas-
ticity, and fibrous shape of the deterior-
ating pellets following the 6-month
storage, required rodding, however, for
them to flow out of the feed hopper. In
the bunker, the coal: d-RDF blend would
"rat hole" and demonstrate angles of
repose in excess of 90°. Bunker vibrators
and air blasters did not eliminate the
need to manually rod the fuel blend into
the nonsegregating distribution chutes
feeding out of the bunker. Very little
modification of the existing fuel-
handling system was required—only a
crusher bypass plate and a backstop at a
conveyor transfer were installed. Other-
wise the fuel handling system was used
as it existed.
When compared with coal, the d-RDF
blends required more frequent ash
removal because of the increased ash
content and decreased heating value of
the fuel. Except for the manual removal
of the infrequent clinkers, no ash
handling problems were noted with the
pneumatic ash handling system.
At a 1:2 (coal:d-RDF) volumetric blend
ratio, a 2 to 3 percent reduction in boiler
efficiency was experienced because of
the increased flue gas moisture formed
in d-RDF combustion. When firing at full
load with coal:d-RDF blends, the com-
bustion flame was observed to require
considerably more combustion volume.
Puffs of flame were observed in the
screen tube section. This increased
flame activity is directly associated with
the higher volatile content of d-RDF as
compared with that of coal. No signif-
icant increases in hydrocarbons or
carbon monoxide were detected in the
flue gas, however.
The combustion of d-RDF blends
exhibited the same range of paniculate
emission rates as coal only. Mass rate of
particulate emissions was measured for
every test at the electrostatic precipitator
inlet. This location was selected because
the particulate characteristics of any
uncontrolled boiler would probably be
similar to those measured at this
location in the system. To measure
precipitator efficiency during periods
when the boiler was operated at
capacity, simultaneous measurements
of particulate concentrations were
made both upstream and downstream
of the electrostatic precipitator. The
electrostatic precipitator performance
was unchanged by the substitution of d-
RDF for coal.
Lead emissions increased by a factor
of six. Cadmium, zinc, and chromium
emissions increased 50 to 100 percent
when firing d-RDF. The substitution of
d-RDF for coal had no significant effect
on NOx, CO, or hydrocarbon emissions.
But, as expected, d-RDF caused a 30 to
50 percent decrease in SO, emissions.
Discussion
The principal objective of the effort
described herein was a demonstration
test. Thus, all testing was performed
under typical power plant operating
conditions. The realities of plant opera-
tion meant that control of the test
conditions (i.e., of the predictive or
"independent" variables of the experi-
ment) was not as tight as could be
expected in a laboratory situation. This
gives rise to much apparent scatter in
the data with concommitant uncertainty
in the results. Such lack of tight control
is not unexpected, and in fact, is
representative of everyday power plant
operation.
In general, this test clearly demon-
strated that co-firing coal and d-RDF can
be performed with minimal impact on
the operational performance of an
industrial power plant. The boiler
performed well, demonstrating an
ability to deliver maximum rated steam
capacity with adequate boiler response
and fuel burnout at coal:d-RDF blends
up to 1:4 (by volume). A slight decrease
in boiler efficiency (2.5 percent drop)
occurred during blend firing. This drop
was attributed to the high moisture and
hydrogen content of the RDF pellets.
There was no significant difference in
particulate emissions at either the
electrostatic precipitator (ESP) inlet or
outlet as a result of firing with blends.
ESP collection efficiency was not
affected by the blend firing. Increases in
heavy metals (i.e., lead, cadmium, zinc,
chromium) and chloride emissions were
noted. Sulfur emissions decreased as
the d-RDF substitution was increased.
The full report was submitted in
fulfillment of Contract No. 68-03-2426
by the Systems Technology Corporation,
Xenia, OH 45385, under the sponsorship
of the U.S. Environmental Protection
Agency.
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The EPA author Matt Stoermer is with the Municipal Environmental Research
Laboratory, Cincinnati, OH 45268.
Car/ton C. Wiles is the EPA Project Officer (see below).
The complete reports were authored by N. J. Kleinhenz of Systems Technology
Corporation, 245 North Valley Road, Xenia, OH 45385, and are entitled,
"Coal:dRDF Demonstration Test in an IndustrialSpreader Stoker Boiler. Use of
Coal:dRDF Blends in Stoker-Fired Boilers":
Volume I. (Order No. PB 82-100 868; Cost: $12.50, subject to change)
Volume II. Appendices A, B, C, and D (Order No. PB 82-100 876; Cost:
$18.50, subject to change)
will b'e available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
U S GOVERNMENT PRINTING OFFICE, 1981 — 559-017/7378
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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