United States Environmental Protection Agency Municipal Environmental Research ^ Laboratory Cincinnati OH 45268 Research and Development EPA-600/S2-84-010 Jan. 1984 &ERA Project Summary Conversion of Sewage Sludge to Oil by Hydroliquefaction Wilmer L. Kranich and Atal E. Eralp A study was undertaken to determine the feasibility of converting municipal wastewater sludges into oil under hydrogen pressure. In a laboratory autoclave, raw and digested sludges were subjected to 14 MPa (2000 psig) total pressure for 20 to 90 minutes. Aqueous suspensions were treated at about 300°C, and predried sludge sus- pended in an oil carrier was reacted at about 425°C. When the predried sludge solids were suspended in an oil carrier, 50 percent of the organic content of sludge was converted into pentane- soluble oil; but significant amounts of oil were not produced under the condi- tions studied when the sludge solids were slurried in water. A commercial plant using the oil carrier process scheme would be complex with high capital and operating costs. Conse- quently, further development work on hydro-liquefaction of sewage sludge is not recommended. This Project Summary was developed by EPA's Municipal Environmental 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 This study was undertaken to assess the feasibility of converting municipal wastewater sludge to liquid and gaseous fuels through reactions with hydrogen at high pressure and temperature. The work was based on earlier experiments carried out in the Resource Recovery Laboratory at the Worcester Polytechnic Institute. In the earlier studies ft-cellulose and powdered newspaper were used to model the behavior of combustible municipal solid waste (J. A. Kaufman and A. H. Weiss; 1975; Solid Wastes Conversion: Cellulose Liquefaction; NTIS Report PB 235-509, National Technical Information Service, Springfield, Virginia 22161). These studies involved the hydrolique- faction and hydrogasification over nickel catalysts of cellulosic substances slurried in paraffin oil at temperatures of 350° to 450°C under hydrogen pressure in the range of 3 to 8 MPa (1150 psig). Under such conditions, up to 90 percent of cellulosic substances can beconvertedto gaseous and liquid fuels. The background, techniques, and experimental equipment associated with the cellulose and lignite liquefaction studies have been applied in the present investigation to the hydro- liquefaction and gasification of sewage sludge. Experimental Procedures For this study, raw and digested sludges were collected from the Deer Island Sewage Treatment Plant in Mas- sachusetts. These samples were used in experiments either as aqueous suspen- sions as received or as suspensions of dried sludge solids slurried in anthracene or paraffin oil. Experiments were carried out in an autoclave under hydrogen pressure. The principal apparatus consisted of a magnetically stirred batch autoclave. Maximum safe pressure that could be applied to this autoclave was 14 MPa (2000 psig). Auxiliary equipment included a hydrogen-feed system, a slurry-feed device, pressure and temperature recorder-controllers, a wet- test meter for measuring the off-gas, and analytical equipment for determining the mass and composition of the liquid and ------- gaseous products. Conditions for experiments are listed in Table 1. the Table 1. Conditions for the Oil and Water Slurry Experiments Experiment Oil slurry Water slurry Initial H2 Operating pressure tempera- (MPa) ture (°C) 8.3 (1200 psig) 425 3,5 (500 psig) 300 With the total pressure limited to 14 MPa (2000 psig), it was necessary to use lower initial hydrogen pressures and temperatures for the water slurry experi- ments because of the vapor pressure generated by the water. The conversion nearly reached its maximum after about 20 min at reaction temperature; little further conversion was observed after 30 mm. Results are evaluated in terms of the total fractional conversion of the toluene- insoluble organic feed into oils (pentane- soluble substancesjand into other substances. These are calculated by the following relationships: Conversion to Pentane-Soluble Oil, XQ = (weight of oils in product slurry) (weight of oils in - sewage sludge and carrier oil) x 100 (weight of organic toluene-insolubles in sewage sludge) Conversion of Toluene-insolubles, XT! = (weight of organic (weight of organic toluene-insolubles - toluene-insolubles in sewage sludge) in product slurry) x 100 (weight of organic toluene-insolubles in sewage sludge) Thus Xo represents the net oil yield per unit of insoluble organic material in sewage sludge, and XTI represents the conversion of the insoluble organic material in sewage sludge to all liquidand gaseous products. Results and Conclusions 1. Raw sewage sludge and sludge settled in digesters can be largely converted to liquid and gaseous products by heating the water slurry to about 300°C under its vapor pressure. Conversion of up to 90 percent of the toluene-insoluble organic feed can be achieved with or without added hydrogen. Neither sodium carbonate, sodium molybdate, nor nickel carbonate catalyst significantly alters the result. 2. Significant amounts of pentane- soluble oils were not produced from the water-slurried sludge under any of the conditions studied 3. If raw or settled digester sludge, or the final effluent sludge from the digesters is dried, ground, and" slurried in a carrier oil, up to 90 percent of the toluene-insoluble organic content can be converted in 20 min in the presence of hydrogen at a total initial pressure of 8.3 MPa (1200 psig) and a temperature of about 425°C. 4. Under these conditions, up to 50 percent of the material so converted may be recovered as pentane- soluble oils or asphaltenes. 5. Great complexity and high projected investment and operating costs of a commercial plant are indicated by the results obtained here for dried sludge slurried with oil. These re- sults do not encourage further development work on hydrolique- faction of sewage sludge. The full report was submitted in fulfill- ment of Cooperative Agreement No. 80739001 by Worcester Polytechnic Institute, Worcester, MA, under the sponsorship of the U.S. Environmental Protection Agency. Wilmer L. Kranich is with Worcester Polytechnic Institute, Worcester, MA 01609. Atal E. Eralp is the EPA Project Officer (see below). The complete report, entitled "Conversion of Sewage Sludge to OilbyHydrolique- faction." (Order No. PB 84-133 768; Cost: $8.50. 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 irUS GOVERNMENT PRINTING OFFICE 1984-759-015/7302 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 BULK RATE POSTAGE & FEES Pf EPA PERMIT No. G-35 Official Business Penalty for Private Use $300 MERL0063240 LOU * TlLtlI REGION V EPA ------- |