United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-83-050 Aug. 1 983
Project Summary
Adaptation of the Simplex
Gasification Process to the
Co-Conversion of Municipal Solid
Waste and Sewage Sludge
J. C. Arbo, D. P. Glaser, M. A Lipowicz, R. B. Schulz, and J. L Spencer
The feasibility of making sturdy bri-
quettes with dewatered sewage sludge
(DSS), municipal solid waste (MSW),
and coal for use in gasifiers was demon-
strated. This investigation consisted of
preparing briquettes with laboratory
equipment and then testing them for
strength, stability, and caking propen-
sity. Parameters investigated included:
coal-to-waste ratio, moisture content,
type of binder, and MSW to DSS ratio.
Optimum conditions were identified
that included 1:1 to 2:1 coal-to-waste
ratio, 12 to 19 percent moisture con-
tent in the finished briquettes, and
MSW-to-DSS ratio of 8 for the 20
percent solids sludge. It was recom-
mended that the findings be confirmed
with the use of commercial briquette
production equipment and in pilot
scale gasifiers.
This Project Summary was developed
by EPA's Municipal Environmental Re-
search 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 Simplex process developed at
Columbia University, New York, converts
cellulosic waste to clean, medium-Btufuel
gas through cogasification with coal. The
principal innovation of Simplex is the
briquetting step, in which coal and cellulo-
sic waste such as MSW or forest pulp are
pressed into briquettes. When these
briquettes are gasified in a moving-bed
gasifier, the waste fibers act as wicks,
absorbing the tars that cause swelling and
agglomeration of caking coal. Because the
briquettes retain their size and shape
throughout the gasifier, the flow of bri-
quettes through the gasifer zones is
smooth and stable.
Simplex was originally developed for
gasification of eastern bituminous caking
coal and refuse-derived fuel (RDF). Muni-
cipalities, however, generate both MSW
and sewage sludge, and it is natural to
dispose of MSW and sludge together.
Codisposal has been applied to several
waste-disposal technologies such as in-
cineration, pyrolysis, and composting.
Codisposal through the Simplex method,
which is called Simplex-S, has several
advantages over these conventional co-
disposal processes. The destruction of
heavy organic wastes in MSW and safe
disposal of heavy metals contained in
sludge are accomplished at a relatively low
cost The nongasifiable components of
Simplex-S briquettes end up embedded in
a glassy, nonleachable frit Thus they can
be disposed of safely or put to use as road-
building aggregates.
The development of Simplex and
Simplex-S processes requires several
steps:
• Phase I: Laboratory Research with
Emphasis on Briquette Development
Briquette formulations that produce
sturdy, noncaking briquettes must
be developed.
• Phase II-A: Process Optimization
Studies with Emphasis on Commer-
cial Briquette Production. The form-
ulations developed in Phase I must
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be tested and adapted to the require-
ments of commercial briquetting
equipment
• Phase II-B: Bench Scale Gasification
Tests. The performance of the bri-
quettes produced in II-A will be
evaluated in the 4-ton-per-day pro-
totype Simplex unit m the Fossil
Energy Laboratory of Columbia Uni-
versity.
• Phase III: Pilot Plant Gasification
Tests. Commercially produced bri-
quettes should be evaluated in pilot
plant runs in which material balances,
throughput rates, and process ef-
ficiencies can be determined.
Because the Simplex development is
now in its final phase (Phase III) after
successful completion of previous phases,
development of Simplex-S benefits greatly
from the experience gained in the Simplex
development.
The work reported here represents the
first phase of Simplex-S development: the
formulation, fabrication, and testing of
briquettes (composed of coal, RDF, and
DSS) that satisfy the following conditions:
• Briquettes must be of adequate
strength to maintain their structural
integrity as they descend through
the several zones of the gasifier.
• The cellulosic waste must prevent
the fusing and agglomeration that
eastern coals normally exhibit.
• The briquettes must be stable in
storage.
• During briquetting no moisture is to
be expressed which will require
additional treatment and disposal.
Materials and Procedure
The dewatered sewage sludge was ob-
tained from the 25th Ward Water Pollu-
tion Control Plant in New York City and
was approximately 20 percent solids. For
experiments where higher solids content
was desired, the sludge samples were
concentrated to 40 percent in a vacuum
oven at 60°C.
Eastern bituminous coal was screened
to remove preexisting fines and then
crushed and screened to 14 mesh.
RDF fuel consisting primarily of news-
print and plastic was obtained from the
Baltimore County Resource Recovery Facil-
ity, Cockeysville, Maryland, which is op-
erated by Teledyne National.
In preparing briquettes, all materials
(except the RDF) including a binder such
as lime are first mixed together by hand
and RDF is then added and mixed in. This
procedure prevents the RDF from wicking
up moisture prematurely, which results in
poor mixing and lower briquette quality.
The briquettes weigh about 40 g each
and are pillow shaped with dimensions of
6 cm by 6 cm by 3 cm.
To manufacture the briquettes, a pre-
determined amount of material is weighed
out and charged into the die. The plunger
is then inserted and pressed down by
hand. The die assembly is placed in a
manually-pumped hydraulic press. The
press is pumped rapidly to the desired
pressure (35-42 MPa) which is main-
tained for about 10 seconds. The pressure
is then released, and the briquette is
ejected. The ejected briquette is weighed
to determine moisture loss, sealed in a
plastic bag, and labeled for testing.
The strength of the briquettes was de-
termined by the Radial Compression Test,
which measures the resistance of a bri-
quette to compressive forces applied to its
edges. This test, which provides a mea-
sure of the briquettes' resistance to crush-
ing or attrition in the gasifier, was per-
formed on briquettes in two states repre-
sentative of various stages in processing:
• "green" briquettes that have been
freshly pressed with no other treat-
ment, and
• pyrolyzed briquettes that have been
exposed to a nitrogen atmosphere at
870°C for at least 20 minutes.
Based on previous experience with Simplex
briquettes, the minimum radial compres-
sion load of 9 kg was considered satis-
factory.
The tendency of the briquettes to ag-
glomerate and fuse was evaluated by py-
rolyzing a sample of briquettes in an inert
atmosphere. Stacks of three briquettes of
the same composition are placed in an
electric furnace. After the furnace issealed
and is purged with nitrogen, the furnace is
turned on. Heating is maintained until
temperatures have exceeded 870°C for at
least 20 minutes. The furnace is then
turned off and is allowed to cool overnight
while the nitrogen purge is maintained.
After cooling, the pyrolyzed briquettes are
removed and caking propensity is deter-
mined by assigning an Adhesion Index to
the briquette samples according to the
type of adhesion they exhibit and the
amount of finger pressure required to
separate them. The Adhesion Index is a
scale from 1 to 8, where 1 represents no
adhesion after pyrolysis and 8 represents
complete fusion. Maximum acceptable
Adhesion Index is 5, which represents a
line contact between briquettes that re-
quires moderate finger pressure to separate.
Experimental Results
The mam purpose of the experiments
was to determine the maximum amount of
sludge that could be incorporated into
briquettes to satisfy certain conditions
deemed desirable based on Simplex ex-
perience. For this purpose the following
variables were investigated: coal-to-waste
(RDF + DSS) ratio (1:1 and 2:1), RDF-to-
DSS weight ratio (1:1 to 1 5:1), and per-
centage of sewage sludge solids (20% to
40%). Ratios are reported on a dry weight
basis.
The major parameters measured were:
1. moisture level of briquettes because
it is a good indication of the stability
and strength of briquettes and it also
serves as a unifying parameter for
the major variables investigated;
2. radial fracture load because it is the
principal criterion for evaluating
strength;
3. percent moisture expressed during
briquetting because moisture loss
would create an undesirable effluent
stream; and
4. Adhesion Index, the main measure
of caking propensity.
Typical experimental results are pre-
sented in Tables 1 -3.
Discussion
Based on the requirement that the bri-
quettes should withstand at least a 9 kg 4
radial fracture load, the test results indi- "
cate that a minimum RDF: DSS ratio for
briquettes with 20 percent solids DSS and
a 1:1 coal-to-waste ratio is about 8:1,
whereas the mimimum ratio is about
2.5:1 for briquettes with 40 percent
solids DSS. When the coal-to-waste ratio
is increased, although RDF-to-DSS ratio
decreases, the percentage of sludge in-
corporated in the briquettes does not
seem to change significantly.
If we establish the requirement that little
or no water is expressed during briquet-
ting, similar conclusions are reached- the
maximum percentage of DSS in briquettes
is about 5 percent for sludge with 20
percent solids and 8:1 RDF-to-DSS ratio.
Because most of the moisture in the
briquettes was introduced with the DSS,
one can conclude that more sludge solids
can be incorporated in the briquettes
when the solids are introduced as high-
solids DSS. This is demonstrated in Table
2 which shows that for 1:1 coal to waste
ratio briquettes of acceptable quality are
obtained with about 14 percent sludge,
when a 2.5:1 RDF-to-DSS ratio and 40
percent solids sludge is used.
The most significant pyrolysis test re-
sults with 20 percent solid sludge, pre-
sented m Table 3 were: ^
a) Pyrolyzed briquettes with a 1:1 coal ^
to waste ratio were weaker in radial
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Table 1. Moisture Level and Radial Fracture Load of Briquettes
20% Solids Sludge 40% Solids Sludge
(low solids DSSJ (high solids DSS)
Moisture Radial Fracture Moisture Radial Fracture
Coal: Waste RDF: DSS Level (%) Load (kgfj Level (%) Load (kg f)
1:1 15:1 15 13 13 17
10:1 19 12 13 15
5:1 27 8 18 14
3:1 35 8 23 14
2:1 41 6 27 8
1:1 N.A N.A 34 6
2:1 15:1 12 17 14 16
10:1 15 11 13 15
5:1 21 12 14 15
3:1 28 9 18 15
2:1 33 6 21 17
1:1 N.A N.A 25 10
Table 2. Moisture Loss During Compaction
20% Solids Sludge 40% Solids Sludge
(low-solids DSSJ (high-solids DSS)
Moisture Moisture Moisture Moisture
Coal: Waste RDF: DSS Level (%) Expressed (%)* Level (%) Expressed (%)*
1:1 15:1 15 0 13 0
10:1 19 0 13 0
5:1 27 6 18 1
3:1 35 10 23 1
2:1 41 17 27 1
1:1 N.A N.A 34 2
2:1 15:1 12 0 14 0
10:1 15 0 13 0
5:1 21 4 14 1
3:1 28 7 18 1
2:1 33 9 21 1
1:1 N.A N.A 25 2
* Accuracy only about ± 2 percent.
Table 3. Pyro lysis Results for Simplex- S Briquettes
Coal: Waste Radial Fracture Adhesion Index
Sludge Type (20% solids) RDF: DSS Load (kg f> (8 = highest)
Raw 1:1 15:1 8 2
10:1 9 2.5
5:1 4 2.5
2:1 15:1 21 5
10:1 13 5
5:1 6 4.5
Digested 1:1 15:1 9 2.5
10:1 11 2
5:1 6 3
2:1 15:1 35 3
10:1 17 3,5
5:1 17 3
fracture load test than briquettes surpassed the maximum acceptable Ad-
with2:1 coal-to-waste ratio. hesion Index of 5 and more than halfofthe
b) Adhesion was higher for briquettes formulas had strengths over 9 kg.
with 2:1 coal-to-waste ratio. Tests with high solids content sludge
Thus, the level of coal had the most also gave similar results
effect High coal levels gave higher strength In addition to the major findings pre-
but higher adhesion, indicating that levels sented above, several other aspects of
too high or low will give inadequate per- briquetting were also investigated, with
formance However, none of the briquettes the full details presented in the main
report. In summary, it was found that
unslaked lime was superior to slaked lime
as an additive. Briquette strength gen-
erally increased as the lime level increased
from 0 to 5 percent More importantly,
lime levels above 3 percent completely
prevented fungal growth in humid envi-
ronments for at least 4 weeks.
The loss in stength with storage was
also investigated. In general, briquettes
with a 5:1 RDF-to-DSS ratio showed less
than 5 percent loss during 8 weeks of
storage whereas briquettes with a 15:1
RDF-to-DSS ratio lost 20 to 40 percent of
their initial strength. This was attributed to
the high content of spongy paper in the
briquettes.
The briquettes were also subjected to
alternating freezing and thawing condi-
tions. Although there was some decline in
strength, it was not as severe as one might
expect from a material with a relatively
high water content such as these bri-
quettes.
Conclusions
The experimental work showed that
briquettes made with dewatered sewage
sludge can be formulated and fabricated to
met the feed requirements of a slagging
gasifier. The criteria for satisfactory bri-
quettes were:
• 9 kg mimimum radial compression
strength
• little or no adhesion during pyrolysis
• no expression of moisture during
briquetting
• stability in storage
These laboratory-scale results can be ex-
tended to the pilot scale with high confi-
dence because past scale-up experience
in the Simplex project showed that com-
mercial briquetting equipment performed
better than laboratory equipment
Several formulation variables had strong
effects on the properties of briquettes;
sludge moisture content level of sludge
solids in briquettes, and level of lime were
the most important factors determining
the quality of freshly pressed briquettes.
The level of coal (or coal-to-waste ratio)
had less effect on the properties of freshly
pressed briquettes but had strong effects
on the strength and adhesion levels of
pyrolyzed briquettes.
Sludge Moisture Content
The amount of DSS that can be success-
fully incorporated in briquettes is limited
by the amount of water added with the
sludge. The experiments showed that the
practical limit for briquette moisture con-
tent is 1 8 to 20 percent by weight Thus,
the maximum level of DSS that can be
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included in 2:1 coal-to-waste briquettes
is determined by the percent solids in the
DSS: approximately 3.4 percent sludge
solids for DSS with 20 percent sludge
solids; approximately 8.8 percent sludge
solids for DSS with 40 percent sludge
solids.
If the moisture level is above the 20
percent limit, then briquettes may fail to
meet one or more criteria: moisture may
be expressed during the high-pressure
briquetting step or briquettes may not be
strong enough to withstand handling.
Because the 20 percent limit is based on
testing with laboratory equipment, bri-
quettes made with commercial equipment
may have higher moisture tolerance: com-
mercial equipment presses briquettes
faster, which may prevent moisture loss
and commercially-pressed briquettes are
generally stronger than laboratory-pressed
briquettes. A higher tolerance for moisture
would allow larger amounts of DSS to be
incorporated into briquettes.
Binders
Unslaked lime was shown to be an
essential briquette component and the
most effective of the binders tested. At 3
percent by weight and above, unslaked
lime enhanced briquette strength and pre-
vented fungal growth. Below 3 percent,
the briquettes may be weak and suscept-
ible to fungal growth. The ideal level
appears to be 5 percent because levels
above 5 percent do not improve strength.
Coal-to-Waste Ratio
The ratio of coal to DSS and RDF had
little effect on freshly prepared briquette
strength or storage characteristics-the
only effects are attributed to the effects of
moisture. But the coal-to-waste ratio did
affect the pyrolyzed strength and the
caking tendency of briquettes: pyrolyzed
briquettes with a 1:1 coal-to-waste ratio
were marginal in strength but showed
little caking tendency; pyrolyzed briquettes
with a 2:1 coal-to-waste ratio had good
strength but marginally acceptable caking
tendency. Because strength is more im-
portant, the 2:1 ratio is the better of the
two ratios tested; however, an intermediate
ratio~e.g., 3:2--is probably better than
either.
Recommendations for Future
Work
The tests and evaluations performed in
this program demonstrated the technical
feasibility of incorporating DSS in Simplex
briquettes. Laboratory scale tests also
indicate that these briquettes have suit-
able properties as a feed for a moving-
burden slagging gasifier.
However, before the Simplex-S process
is applied in full-scale gasification, testing
in commercial-scale mixing and briquetting
equipment would be desirable. Because
the commercial press produces thicker
briquettes at a faster rate with more pres-
sure, some of the formulas that were
marginal in this experimental program
may prove satisfactory in a commercial
briquetting operation. Among the results
that should be examined are:
• Moisture expression: determine max-
imum briquette moisture levels, ex-
amine methods of handling expressed
moisture from high-moisture bri-
quettes, and test effects of produc-
tion rate and compaction pressure.
• High moisture RDF: fabricate bri-
quettes using RDF with moisture
representative of RDF freshly pre-
pared from urban waste.
• Briquette strength: determine max-
imum briquette moisture levels, and
test the effects of mixing, compac-
tion pressure, and precompaction on
briquette strength.
In addition to verifying the results of this
experimental program, future work should
address the mixing and feeding opera-
tions that are necessary in commercial-
scale briquetting.
The full report was submitted in fulfill-
ment of Cooperative Agreement No. CR
806998010 by the New York State
Energy Research and Development Author-
ity under the partial sponsorship of the
U.S. Environmental Protection Agency.
J. C. Arbo, D. P. Glaser. M. A. Lipowicz. R. B. Schulz. and J. L. Spencer are with
Dynocology Incorporated, Harrison. NY 10528.
Atal E. Eralp is the EPA Project Officer (see below).
The complete report, entitled "Adaptation of the Simplex Gasification Process to
the Co-Conversion of Municipal Solid Waste and Sewage Sludge," (Order No.
PB 82-112 418; 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 Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
*US GOVERNMENT PRINTING OFFICE- 1983-659-017/7163
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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