United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-050 Apr. 1981
Project Summary
Selective Enhancement of
RDF Fuels
N L Meet, D. S. Duvall, A. A. Ghazee, and B. L. Fox
Conversion of the organic fraction
of municipal solid waste (MSW) to a
powdered fuel offers a number of
advantages for improving both the
quality and marketability of the
product. This project concentrated on
improving the embrittlement process
and characterizing the properties of
the powdered fuel thus obtained. The
combustion characteristics of the
powder alone and the powder mixed
with powdered coal and with oil were
extensively evaluated.
This Project Summary was develop-
ed by EPA's Municipal Environmental
Research Laboratory, Cincinnati, OH,
to announce key findings of the
research project that is fully docu-
mented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
The processes to convert the organic
fraction of MSW to a powdered material
offer a number of advantages for
improving both the quality and market-
ability of refuse-derived products. In the
powdered form the refuse is a more
effective fuel, it can be used as a filler
material in plastic and rubber products
and can be used as a feedstock in
several biomass conversion processes
(acid hydrolysis, pyrolysis, etc )
Characteristics of RDF Powder
Powder Characterization
Over 363 kg (800 Ib) of refuse-derived
fuel (RDF) were processed by embrittle-
ment treatment for conversion to a fine
powder (Table 1). The powder obtained
by the embrittlement of RDF consisted
primarily of short choppy fibers minus
150/u (-100 mesh) in size. Dispersed in
the fibrous mix were irregularly shaped
inert materials, predominantly silicate
glasses The powder contained 5% to 7-
1/2% moisture and 25% to 44% non-
combustibles. The quantity of noncom-
bustibles will vary considerably for
different processes and for different
areas of the country. Analysis indicated
the powder contained about 52% vola-
tiles and had a carbon content of 35%
and a chlorine content of 3%. The
powder had a loose density of 271
kg/m3 (16.9 Ib/ft3) and an average heat
content of 13025 Mj/kg (5600 BTU/lb).
An RDF with a lower inert content
would have a higher heat content. The
inert fraction was calcium-, magne-
sium-, sodium-, aluminum-silicate
Table 1. Powder processing
conditions.
Quantity of RDF
Processed
Processing
temperature
Processing time
HCI flow rate
2.3 kg/5 Ib
149°C (300°F)
3 to 5 mm
439 cm3/sec
(0.93 ft3/mm)
170 cm3/sec
(0.36 ff/min)
HCI adsorbed by RDF 2% by weight
Ball mill time 2 hr
Screening time 1 hr
N2 flow rate
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Table 2. Results of the Combustor Experiments
Fuel
Run
No. Type
1.
2.
2a.
3.
4.
5
6.
Coal
RDF Powder
RDF* Powder
75% CoaF
25% RDF Powder
75% Coal0
25% RDF Powder
50% Coal0
50% RDF Powder
50% Coal0
50% RDF Powder
Feed
kg/hr
0.54
<0.9
<0.9
0.54
0.9
0.9
1.36
Rate
.(Ib/hr)
(1.2)
«2)
«2)
d)
(2)
(2)
(3)
Wall
Avt
°C
946
899
871
963
899
960
935
Temp3 A
?rage
(°F) Ft
(1735)
(1650)
(1600)
(1765)
(1650)
(1760)
(1715)
pproximati
Residence
Time in
jrnace, set
0.85
3.71
~4
2.06
0.96
0.98
0.93
Q
". CO
550
100
<300
550
320
140
220
ppm
S02 NO
2800 550
60 150
—
2200
2000
7500
7500
Weight %
% (in ash)
C02
73.0
14.4
—
15.8
16.0
16.4
14.4
02
6
9
10.5
6
6
5
3
C
13.2
8.1
1.2
24.1
11.9
4.0
9.6
H
0.2
0.3
.._
05
0.2
0.2
0.2
"Thermocouple readings at 7 27 cm (0 5 in) from inside wall, inside wall temperature approximately 204°C (400°F) higher
"Minus 74/j (-200 mesh) RDF powder, and all other fuels minus 149p (-100 mesh)
'Weight percent basis
glass, low in iron The fusion tempera-
ture was above 1360°C (2480°F). The
RDF powder was easily ignited and
burned readily
When compared with powdered coal,
the RDF powder had a lower ignition
temperature, higher volatile content,
much lower carbon, about half the heat,
twice the ash, one-tenth the sulfur, and
15 times the chlorine, and was four-
tenths the density. As a fuel, the RDF
powder will ignite and burn more rapidly
than coal but generates less thermal
energy. Combustion products will
present about as much corrosion prob-
lems as coal (Cl versus S) but should
present greater handling problems
because of a lower density and high ash
content.
Powder/Oil Slurries
Suspension of the RDF powder in a
fuel oil offers a number of advantages
for enhancing the use of the RDF
powder as a fuel, easier transport and
storage, greater safety, etc The proce-
dure for preparing powder/oil slurries
and selected properties were evaluated.
The powdered RDF can be easily
slurned in oil, up to about 40 weight
percent. The only problem was the sedi-
mentation of the powder within 4 hours
More stable suspensions (exceeding 20
hours) were obtained with small (1%)
additions of the dispersion agent
(Rheotol*). As would be expected, the
density and viscosity of the powder/oil
slurry is considerably higher than the
pure fuel oil. Stabilized slurry does not
appear to present transport and
handling difficulties, although long-
term experience with these fuel
mixtures will be required
Combustor Experiments
RDF Powder and RDF
Powder/Coal Mixtures
The RDF powder and mixtures of 25
and 50 weight percent RDF powder with
coal were fired in a pulverized coal test
Combustor Although some handling
problems were encountered with the
RDF powder because of its lower
density and heat content, the RDF
powder/coal mixtures (particularly the
50/50 blend) handled very well and all
the compositions tested burned well
(Table 2) In addition to its good handling
characteristics, the 50/50 blend proved
to be the most effective fuel mix studied
The lower ignition temperature and
higher quantity of volatiles in the RDF
aided the combustion of the coal
"Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use by the U S Environmental Protection
Agency
The coal was also more completely
combusted when it was mixed with the
RDF powder The very low sulfur anc
alkali content of the RDF powder effec
tively reduced SOa in the combustior
gas emissions. The high chlorine
content in the RDF powder may, how
ever, cause corrosion problems anc
some environmental concerns. The use
of a less corrosive embrittling agen
(e g., HN03, H3PO4, O3, H2O2, etc ), i
effective, could reduce or eliminate thi:
problem.
RDF Powder/Oil Slurries
The RDF powder/oil slurries with up
to 30 weight percent RDF burned well ir
the test furnace. Above the 15 weigh
percent, however, there were a numbei
of problems m transporting the slurry
The primary problem was powder sedi
mentation plugging the pump and feec
lines Using a dispersion agent shouk
alleviate this problem The combustior
of the powder/oil slurries producec
considerably more ash than isobtamec
when the oil is burned alone. Thi<
causes handling problems since the
conventional oil burning units are no
designed to process large quantities o
ash The ash content of the RDF powde
is likely to be the limiting factor fo
determining the RDFpowder-to-oil rati<
for slurry preparation
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Conclusions
An effective procedure for converting
RDF to a fine powder by embrittlement
treatment was developed. The RDF
powder appears to be an effective fuel
compatible with coal and some oil burn-
ing equipment. Although the RDF
powder can be burned alone or in
combination with coal and oil, its best
performance was in a mix with pulver-
ized coal—as a 50/50 mix This fuel
mixture burns well (better than either
component) and results in lower SOs
emissions
The major difficulties with using the
RDF powder as a fuel is the high inert
content (ash) and the potential problems
from the high chlorine content Using
screening and other classification
processing of the raw refuse should
significantly reduce the inert content,
and using different embrittlement
reagents (HNO3, H3P04, etc ) should
eliminate potential corrosion and
environmental problems Additional
research studies will be required, how-
ever, to select effective unit processing
procedures that will reduce inert
content and to select a less corrosive
embrittlement agent
In the course of this work, a technol-
ogy for converting refuse to a fine
powder was established based on the
use of cellulose embrittlement tech-
niques. The mechanisms of the process
are not completely understood, how-
ever, and need further elucidation
Identifying effective alternative embrit-
tlement reagents, particularly reagents
that would not leave corrosive or detri-
mental residues, is also needed.
The RDF powder, when used in a
50/50 (by weight percent) mix with
pulverized coal, enhanced combustion
of the coal More needs to be known,
however, about the handling (transport,
storage, etc ) behavior of both the RDF
powder and the powder in a 50/50 mix
with pulverized coal. In addition, more
needs to be known about the emissions
from combustion of RDF/coal mixtures.
Apparently a variety of biomass
materials, particularly cellulose wastes
from industrial and agricultural sources
(stalks, husks, bark, wood and crop
residue, straw, etc.) could also be
converted to a powder for use as a fuel
or as a feedstock for biomass conver-
sions Effective processing procedures
for powdering the variety of biomass
materials that might be available for
conversion to a powdered fuel are
needed
Based on these observations, the fol-
lowing recommendations for future
work are proposed (1) further elucida-
tion of the embrittlement mechanisms;
(2) identification of alternate embrittle-
ment reagents; (3) further characteriza-
tion of the RDF powder mixed with
pulverized coal; and (4) extention of the
embrittlement process to other biomass
materials
This work was conducted in fulfill-
ment of Grant No. R-806535010by the
University of Dayton Research Institute
under the sponsorship of the U.S. Envi-
ronmental Protection Agency
N. L. Hect, D S. Duvall, A. A Ghazee, and B. L Fox are with the University of
Dayton Research Institute, Dayton. OH 45469.
Stephen C. James is the EPA Project Officer (see below).
The complete report, entitled "Selective Enhancement of RDF Fuels," (Order No.
PB 81-179 269; Cost: $8.OO, 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:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati. OH 45268
f US GOVERNMENT PRINTING OFFICE 1981-757-012/7100
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