United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-178 Dec. 1984
Project Summary
If
Environmental Effects of
Utilizing Solid Waste as a
Supplementary Power Plant
Fuel
D. A. Vaughan, H. H. Krause, P. W. Cover, R. W. Sexton, and W. K. Boyd
The results of three years of research
on the utilization of shredded and mag-
netically separated municipal refuse to
supplement high-sulfur coal as fuel in a
stoker-fired boiler are presented. The
facilities of the Columbus, Ohio, Munic-
ipal Electric Plant were used for this
program. During the first half of the
research, a refuse handling and furnace
feed system consisting of agriculture
crop handling equipment was used.
With this equipment, the feasibility of
blowing shredded refuse into a boiler
and burning it completely on a traveling
grate was demonstrated. Corrosion
probe exposures were used to show the
effectiveness of cofiring to reduce short-
term corrosion of boiler tube metals.
Reduced emissions of sulfur dioxide
(SO2} from the high-sulfur coal also
resulted from dilution of the coal with
refuse and by action of alkaline com-
ponents of the refuse.
To study the handling and combustion
of larger amounts of shredded refuse
and to measure long-term corrosion
effects, an improved system was devel-
oped and installed during the second
half of the program. This system con-
sisted of a hydraulic push-pit, augers,
and a belt to convey the refuse to air-
swept spouts that injected the refuse
into the boiler. Amounts of refuse up to
6800 kg/hr (7.5 tons per hour) were
burned successfully using this system.
It was demonstrated that 700-hour
corrosion rates with an average of 22
weight percent refuse and high-sulfur
coal were 5 to 10 times less than those
with bulk refuse burning and about
equal to those from coal alone. Sulfur
dioxide emissions were reduced as a
function of the refuse content of the
mixture. The cof iring with refuse had no
significant effect on particulate loading
of the flue gases, fly ash resistivity, or
grate ash composition, but the ash
fusion temperature was lowered some-
what.
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).
Introduction
The objective of this research program
was to develop technology for the utiliza-
tion of municipal refuse as a supple-
mentary fuel in coal-fired power or steam
generating plants. Three aspects of this
technology were investigated: (1) the
preparation and handling of the refuse
before burning, (2) the corrosivity of the
mixed fuel to boiler tubes, and (3) the
emissions and residues resulting from
the burning of the mixed fuel. As a result
of previous Battelle investigations, which
demonstrated that the corrosivity of the
combustion products from municipal solid
waste could be reduced by the addition of
sulfur, it was proposed that disposal of
municipal refuse in boiler furnaces util-
izing high-sulfur coal would not be detri-
mental to boiler tubes. In addition, the
dilution of the coal with the refuse and
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the reaction of sulfur oxides with alkaline
components of solid waste would reduce
the sulfur oxide emissions to a permiss-
ible level.
To substantiate the above concept and
to develop technologies associated with
the utilization of solid waste as a fuel, the
program investigated the effects of oper-
ational variables on emissions, corrosion,
combustion, and ash properties in the
Columbus, Ohio, Municipal Electric
Plant's spreader-stoker-fired boiler fur-
nace. This site was selected to represent
coal-fired boiler furnaces with grates on
which final burnout of the refuse could
occur.
Although a program on burning of
processed (shredded and classified) solid
waste was conducted at the Union Elec-
tric Company in St. Louis, Missouri, and is
currently operating at the Ames, Iowa,
Electric Utilities, the current program was
directed toward determining the limita-
tions and the benefits of burning the
shredded solid waste with high-sulfur
coal with very little or no processing of the
solid waste except for shredding. Deleting
the classification steps in the processing
made it mandatoryto investigate methods
for receiving, storing, retrieving, and
handling the refuse within the limited
space available at the plant. This work
had to be accomplished before the invest-
igation of corrosion and emissions from
the cofiring process could be evaluated.
During the first year of this program, a
temporary system for handling and feed-
ing the shredded waste to the boiler was
assembled using commercially available
agriculture equipmentfor handling forage
and grain crops.
During the period of development of the
refuse handling system, shredded refuse
from Willoughby, Ohio, and from St.
Louis, Missouri, was obtained for evaluat-
ing the equipment capabilities. Prelim-
inary corrosivity studies on the combined
fuel and the baseline coal fuel were
conducted during the first year. However,
the Sanitation Division of Columbus,
Ohio, started operation of their Jeffrey
shredders in June 1975.
Hence, the second year of this research
was directed towards utilizing Columbus
refuse as a supplement to the coal fuel
and evaluating the handling of this
refuse plus analyzing the emissions and
the corrosivity as the refuse was burned
with high-sulfur coal. Also, the analysis
of a refuse handling system for the
Columbus, Ohio, Municipal Electric Plant
was directed toward the design and
construction of a more rugged system
that would permit long-term investiga-
tions of stack emissions and fireside
corrosion.
The third year of the program consisted
of: (1) procuring and installing the refuse
handling system, (2) optimizing the oper-
ation of the system, (3) conducting long-
term corrosion runs, and (4) making
additional measurements of emissions
and residue characteristics.
Conclusions
The experimental program conducted
atthe Columbus, Ohio, Municipal Electric
Plant demonstrated the technical feasib-
ility of mechanical handling and furnace
feeding of shredded municipal solid waste
at an existing stoker-fired boiler with
limited space and accessibility. Also, it
has been shown that the refuse can be
burned completely on a grate in conjunc-
tion with coal, utilizing a spreader-stoker.
The corrosivity of the combustion prod-
ucts from refuse burned with high-sulfur
coal was reduced significantly from that
for refuse alone and was essentially
attributable to the sulfur in the coal. The
sulfur oxide emissions were reduced by
dilution of high-sulfur coal with a very
low-sulfur fuel and by the formation of
stable sulfate particulate compounds
with alkaline refuse components. The ash
residues from the cofiring of refuse and
coal had essentially the same composition
as those from coal alone.
The f ol lowi ngconclusions were reached:
1. The corrosivity of combusiton prod-
ucts from cofiring refuse and three
percent sulfur coal up to a 2 to 1
weight ratio is not significantly
different from that of coal alone.
2. The corrosion rates of boiler tube
metals decrease rapidly with ex-
posure time. After 700 hours, the
rates for stainless steels level off.
3. Boiler tube metals can be ranked in
the following order of increasing
resistance to corrosion: A106 car-
bon steel, P9 low alloy steel, and
Types 316, 347, and 310 stainless
steel.
4. Reductions of S02 as much as 10
percent more than the dilution
effect can be achieved under opti-
mum combustion conditions.
5. Refuse can be burned with coal on a
traveling grate with processing
limited to shredding and magnetic
separation.
6. The ash fusion temperature was
reduced by burning large amounts
of refuse with the high-sulfur coal.
7. The fly-ash resistivity was not
changed significantly by burning
the refuse with the high-sulfur coal.
8. Refuse that has undergone shred-
ding and magnetic separation can
be handled effectively with augers
and belts. A live-bottom feed from
storage is preferable to hydraulic
ram feed.
9. The processed refuse can be fed
successf uIly into the traveling-grate
furnace with air-swept spouts.
10. The shredded refuse, nominally 10
cm (4 inches), will burn out com-
pletely on the traveling grate. The
underfire air supply is a critical
factor in the quality of the refuse
combustion.
11. The aluminum and other low-melt-
ing metals present in unclassified
waste may cause clogging of the
grates if the underfire air is not
properly maintained.
R ecommendations
It is recommended that further develop-
ment of the burning of shredded refuse
with coal on a grate in existing boilers be
encouraged, both to recover energy and
to minimize landfill requirements.
The corrosivity of the combustion prod-
ucts of shredded and magnetically separ-
ated refuse should be investigated when
such refuse is burned alone. Such data
have not been obtained, and it is possible
that the shredding process and removal
of ferrous metals will influence the
corrosion reactions sufficiently to reduce
metal wastage to that experienced with
coal alone.
The corrosive effects of burning very
large amounts of refuse (90 weight
percent) with high-sulfur coal should be
determined. The maximum refuse input
without serious corrosion is not known.
Additives other than sulfur to combat
corrosion should be sought for situations
such as bulk burning of refuse or where
high-sulfur coal is not readily available.
The combustion conditions for shred-
ded refuse and coal should be investi-
gated further to optimize the reduction in
sulfur dioxide emissions and to minimize
the particulate loading of the flue gases.
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D. A. Vaughan, H. H. Krause. P. W. Cover, R. W. Sexton, and W. K. Boydare with
Battelle Columbus Laboratories, Columbus. OH 43201.
Michael!. Black and Robert A. OlexseyaretheEPA Project Officers (see below}.
The complete report, entitled "Environmental Effects of Utilizing Solid Waste as a
Supplementary Power Plant Fuel," (Order No. PB 85-122 422; Cost: $10.00.
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 Officers can be contacted at
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
U S. GOVERNMENT PRINTING OFFICE; 559-016/7863
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
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