United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-85/117 Dec 1985
&EPA Project Summary
Emission Assessment of
Refuse-Derived Fuel
Combustion: Suspension Firing
J. K. Arand, L. J. Muzio, and Rachel L. Barbour
Increased interest in developing ac-
ceptable methods for recovering usable
energy from municipal waste has
brought about the need to investigate
potential emissions from three combus-
tion modes which could be used in
burning refuse-derived fuels (RJDF).
Laboratory-scale experimental studies
were carried out to evaluate fuel/com-
bustion characteristics and emissions
during co-firing of coal and RDF fuels
using:
• grate (or bed) burning
• suspension burning
• fluidized bed burning
The full report presents the results for
suspension firing.
The suspension burning investigation
was conducted in a horizontal laboratory
boiler firing at a nominal heat input of
440 kW. The boiler had been modified
to simulate large utility boilers as well as
to permit co-firing and tri-firing of coal,
RDF. and hazardous liquids. During the
study, the following conditions were
investigated:
RDF type
RDF/coal ratio
RDF/coal/hazardous waste ratio
excess air
staged combustion
hazardous waste type
A powder type RDF was co-fired with
coal at ratios up to 50 percent (heat
input basis) and tri-fired with pulverized
coal and hazardous liquid waste (40
percent/40 percent/20 percent, re-
spectively on a heat input basis). A fluff
type RDF was also co-fired with coal.
Emission measurements were obtain-
ed for a large number of co-fired condi-
tions; many showed reduced nitric oxide
emissions with co-firing relative to
coal-only combustion. Organic and
inorganic samples showed only two
combustion conditions where polynu-
clear aromatic hydrocarbons (PAHs)
were present. Both of these occurred
during tests with tri-fired powder RDF.
coal, and waste oil. Screening tests
showed levels of dioxins and polychlo-
rinated biphenyls (PCBs) were below
threshold values.
Suspension firing of the fluff type
RDF was not satisfactory above 10
percent Btu basis due to incomplete
combustion of the larger particles in the
primary burner.
This Project Summary was developed
by EPA's Hazardous Waste Engineering
Research Laboratory, Cincinnati, OH,
to announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Background and Objectives
Most incinerators which burn munic-
ipal refuse do not produce steam and all
the heat generated is lost. There have
been some attempts to utilize this source
of heat by adding steam or hot water
generating equipment to municipal in-
cinerators. Since most of these heat
recovery effects involved add-on devices,
they were usually of low thermal effi-
ciency when compared to utility or
industrial steam generation boilers.
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Since utility boilers have the potential
for handling large amounts of municipal
solid waste with efficient heat recovery, a
number of feasibility studies on large
utility boilers such as St. Louis/Union
Electric were undertaken. Unfortunately,
large commercial utilities have little eco-
nomic incentive to pursue the use of
refuse-derived fuel (RDF) as a power
plant supplemental fuel because they
have favorable long-term fuel contracts
plus fuel cost pass-through provisions.
On the other hand, smaller industrial
boilers may be a more likely candidate for
using municipal waste as a supplemental
fuel source Based on Federal Energy
Administration estimates, over 15 per-
cent of all the energy consumed in the
United States is utilized by industrial
boilers to generate process steam. The
total annual energy consumption by these
boilers is in excess of 9,300 trillion kJ's
The range of equipment used to com-
bust fuels in either industrial or utility
boilers is wide and the types of fuels are
varied The focus in this research program
was on coal firing using three current
modes of combustion considered suitable
for either sector. These modes are:
• Suspension Firing
• Overfired Stoker Combustion
• Fluidized Bed Combustion
The objective of the overall program
was to obtain an emission assessment of
these three modes of combustion when
co-firmg a base coal and refuse-derived
fuels (RDF). The full report addresses the
evaluation of suspension fired emissions
of co-fired coal and two types of RDF Due
to the increased interest in hazardous
waste disposal, an assessment of co-fired
or tn-fired coal/RDF/hazardous waste
was also included m the program
Experimental Apparatus and
Approach
The experiments were conducted in a
multifuel combustion facility capable of
solids fuel firing rates to 880 kW All of
the experiments in this study were con-
ducted at 440 kW The basis of the
combust ion facility was a780kWfiretube
boiler which had been extensively mod-
ified to simulate utility boiler conditions
This included an indirectly fired air pre-
heater, a scaled-down utility boiler burn-
er, radiation shields to increase the
thermal environment in the combustion
chamber, and capabilities to achieve
staged combustion
The system was set up to allow separate
delivery of the pulverized coal, RDF, and
hazardous liquid waste to the combustion
chamber. The pulverized coal and the
RDF were pneumatically conveyed to the
burner using a portion of the combustion
air. Exhaust ducts were sized to achieve
isokinetic sampling of paniculate emis-
sions. A systematic set of experiments
was conducted which investigated the
following variables:
• RDF type
• RDF/coal ratio on a Btu basis
• RDF/coal/hazardous waste ratio
• Excess air
• Staged combustion
• Hazardous waste type
During the experiments the combustion
products were monitored for O2, C02, CO,
NO, SOa, SOs, opacity, particulate loading,
particulate size distribution, trace ele-
ment, and halogen emissions.
Results
RDF Fuel Handling and
Combustion Characteristics
Two different types of RDF were utilized
in this program; one RDF can be referred
to as a powder and the other a fluff.
The powder RDF was easily combusted
when co-fired with coal in the suspension
firing boiler to heat input fractions of 50
percent RDF. The maximum feed rates of
powder RDF to the boiler were limited by
the fuel supply systems available for the
program rather than any combustion
characteristics of the RDF fuel.
With the fluff RDF it was not possible to
achieve complete combustion of the RDF
in suspension firing above 10 percent
RDF (on a heat input basis). At feed rates
approaching 20 percent the RDF burned
partly in suspension and partly on the
floor of the combustion chamber. The fuel
feed system for the fluff RDF was not
capable of transporting the plastic mater-
ials contained in this type of RDF. Heavy
duty plastic trash bag liners were partic-
ularly difficult to shred and thus caused
numerous solids handling and transport
problems.
Emission Characteristics
Base Coal
The base coal was fired at excess air
levels between 20 percent and 70 percent
for single-stage combustion and at a fixed
excess air level of approximately 30
percent with staged combustion. Emis-
sion characteristics were determined for
gaseous and solid components as a basis
of comparison for the co-fired and tri-
fired tests.
Co-Fired Fuels
Two different RDFs and two different
hazardous waste liquids were co-fired
with the base coal. The criteria emissions
were measured for all test points. These
co-fired tests showed nitric oxide emis-
sions in all cases to be lower than for the
base coal. Carbon monoxide emissions
were unchanged and sulfur oxide emis-
sions were lower as compared to the base
coal.
Limited trace element measurements
and halogen emission measurements
were made. The majority of these measure-
ments were made for various percentages
of the two RDFs co-fired with coal. Chlo-
rine was the major halogen emission and
the concentration increased as the per-
centage of RDF fired was increased.
Principal trace elements found in the flue
gas were those present in the RDF and
coal. Analyses for polynuclear aromatic
hydrocarbons (PAH), polychlorinated bi-
phenyls (PCB), and dioxins, showed con-
centrations were well below levels of
concern for all conditions sampled.
Tri-Fired Fuels
Tri-firmg was accomplished for each of
the two hazardous waste liquids (benzene
and waste lubricating oil) in combination
with coal and the powder RDF.
The conclusions from the measure-
ments made during these tn-fired exper-
iments are the same as for the co-fired
fuels.
Conclusions
The major conclusions that can be
drawn from the results of the study
include:
• The fluff type RDF did not exhibit
acceptable combustion characteristics
at RDF/coal ratios above 10 percent
(on a heat input basis) with pulverized
bituminous coal.
• The powder RDF exhibited suitable
combustion characteristics when co-
fired in suspension firing at ratios up to
50 percent (on a heat input basis) with
pulverized bituminous coal.
• Staged combustion was effective in
reducing nitric oxide emissions for
both RDF/coal combinations. The par-
ticulate emissions increased with
staged combustion.
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The trends observed in NO, emissions
versus excess air were similar for coal
only, co-fired, andtri-fired combustion.
A slightly lower nitric oxide emission
for multifuel combustion compared to
coal-only combustion was observed
Changes in the trace element concen-
trations due to co-firing or tri-firmg
were detected. The increase in chlo-
rine emissions were comparable to the
increase in chlorine content of the RDF
relative to the coal.
For all conditions tested, concentra-
tions of PCBs, PAHs, and dioxins were
within acceptable limits.
J. K. Arand, L. J. Muzio. and R. L Barbour are with KVB. Inc.. Irvine. CA 92714.
Michael Black is the EPA Project Officer (see below).
The complete report, entitled "Emission Assessment of Refuse-Derived Fuel
Combustion: Suspension Firing,'' (Order No. PB86-114 7'25/A S; Cost $16.95,
subject to change) will be 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:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES PA
EPA
PERMIT No. G-35
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Penalty for Private Use $300
EPA/600/S2-85/117
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