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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