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 ------- 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 ------- 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 ------- 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 Postage and Fees Paid Environmental Protection Agency EPA 335 Official Business Penalty for Private Use $300 RETURN POSTAGE GUARANTEED SS3 ENVI^PROTECTION AGENCY REGIUN 5 LIBRARY <>30 S UtAKBORN STREET CHICAGO IL 60004 ------- |