Iv o xm r Mobile incinerator for toxic wastes I
By Gopal D. Gupta
kaching and runoff from toxic materials at abandoned hazardous waste landfills pose severe threats to human health and the environment. Motivated by this, EPA instituted research and development projects as early as 1982 aimed at cleaning up these sites. Trials designed to treat the toxic wastes at the sites, and so escape the need for transportation of hazardous wastes, were put into effect over a number of years using the most promising v&s are insigh@/ comnraries on timely environmental topics. represent an aurhor's opinion, and do not necessarily represeiu a position of the society or editors. Connastinn views are invited,
equipment-including the Mobile Jncineration System (MIS) developed by EPA's Releases Control Branch of the Risk Reduction Engineering Laboratory in Edison, NJ. Throughout eight years of research, EPA continued to refine the MIS. Extensive modifications were made by Foster Wheeler Enviresponse, Inc. (FWEI), a subsidiary of Foster Wheeler Corporation (Clinton, NJ), in concert with EPA. Between February 1988 and April 1989, a total of 8,930,000 Ibs of solids and 30,500 Ibs of liquids were incinerated-including more than 2,150.000 Ibs of dioxin-contaminated brominated sludge-at one site, the Denney Farm in southwestern Missouri. A total of
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12,500,000 Ibs of solids and 230,000 Ibs of liquids from eight dioxin-contaminated sites were incinerated between 1985 and 1989. In 1989, MIS operations at the Denney Farm ceased; the site was considered free of toxic contaminants and was closed. The MIS technology, as it has advanced from 1982 to the present, has solved a number of engineering problems and provided toxic waste removal benefits. As currently constituted, on the first of the four semitrailers making up the MIS is a kiln in which organic wastes are fully vaporized and at least partially oxidized. Incombustible and nonhmardous ash is discharged directly from the kiln. The gas from the kiln passes
0013.936w90/0924-1776$02.5010 @ 1990 American Chemical Societv
through a cyclone where additional particulate matter is removed. The gas then flows to a secondary combustion chamber (SCC) on the second trailer where oxidation of the contaminants is completed at 2200 OF. The flue gas exits from the SCC and is cooled hy watersprays to approximately 190 "F, with
Gopal Gupra
substances, such as chlorine or phosphorous, are captured by the air pollution control equipment and thus prevented from escaping to the atmosphere. System performance is maintained through instrument measurements and automatic safety controls. Continuous monitors measure temperatures, pressures, flow rates, and stack gas composition. The system is also continuously monitored and can be controlled by an operator. In 1989, the MIS was decontaminated, disassembled, and transported to EPA's Environmental Technology and Engineering Facility in Edison, NJ. EPA intends to transfer the technology involved in the MIS to the private sector. This augurs well for the future of the process and its technological and economic improvement.
excess water collected in a sump. The gas then passes into the wet electrostatic precipitator (WEP)and on to the masstransfer scmhber on the third trailer. In the WEP, submicron particles are removed from the gas stream. By-product acid gases generated by the destruction process are neutralized in the alkaline mass-transfer scrubber. Gases are drawn through the system by an induced-draft fan, which maintains the system under vacuum to ensure that no toxic gases escape from the system. Finally, the cleaned gases are discharged from the system through a 40-foot-high stack. Generally, the hazardous organic wastes containing carbon and hydrogen are converted by the system into harmless carbon dioxide and water vapor. Other
Background developments Comprehensive tests qualified the equipment for the permits necessary for full-scale operation as a hazardous waste incinerator. These included trial bums, delisting tests, equipment shakedown, and full-scale demonstrations. The results of these tests showed that the MIS could meet Resource Conservation and Recovery Act (RCRA) requirements for destroying dioxin-contaminated solids and liquid wastes. The basic design objectives for the MIS were complete combustion of organic compounds at temperatures typically over 1600 "F in an oxidizing environment, and capture of incineration byproducts. Release of acid gases, heavy metals, and particulates were to be minimized by air pollution control equipment. Originally, the MIS was made up of incineration and air pollution control equipment mounted on three heavy-duty semitrailers, combustion and stack gas monitoring equipment housed in a fourth trailer, and ancillary support equipment. The incinerator and air pollution control system consisted princi-
pally of a half dozen components: a rotary kiln, an SCC, a wetted throat quench elbow with sump, a cleanable high-efficiency air filter (CHEAF), a mass-transfer scrubber, and an induceddraft fan. Ancillary support equipment consisted of bulk fuel storage, waste blending and feed equipment for both liquids and solids, scrubber solution feed equipment, ash receiving drums, and auxiliary diesel power equipment. After rigorous testing of the MIS on polychlorinated biphenyl (F'CB)-contaminated liquids and other chlorinated organic fluids in Edison, NJ, during 1982 and 1983, the system was modified to encompass incineration of solid wastes. In December 1984, the MIS was transported to an abandoned waste site at the Denney Farm, near McDowell, MO, for a trial burn on dioxin-contaminated solids and liquids and for a subsequent field demonstration. More than 90 buried drums nf dioxincontaminated wastes had been found at the Denney Farm. These drums had sprung leaks, contaminating more than 6300 ti3of soil. Beginning in June 1985, FWEl provided research, engineering, design, operation, maintenance, management, and technical reporting services for the further development and demonstration of the MIS at this site. During the initial field demonstration at the Denney Farm site, the MIS had shown its ability to destroy liquid and solid hazardous wastes, but showed a relatively low on-stream time of about 40% and a low throughput rate for lowmOiSNE, high-hat wastes. In February 1986, a design study aimed at increasing the MIS capacity and on-stream service factor was undertaken. The study found two main reasons for the low on-stream service factor: excessive particulate wryover from the rotary kiln which accumulated in the SCC, requiring a several-day cooling down and cleanout period and, second, the extensive maintenance required on the CHEAF. It was also determined that the gas residence time in the SCC limited the soils' throughput of the MIS unit. Improvements that increased the system's capacity were made in early 1987. The trough of the ram feeder was enlarged to feed a greater volume per ram stroke. An innovative all-oxygen burner, Linde Oxygen Combustion System (OCS), replaced one of the conventional air burners to reduce the gas flow rate. The feed capacity could then be increased without going below the required two-second gas residence time for the SCC. confinuedon p. 1780
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not contaminated, although it had been in the past. Brown Wood Preserving, FL. The HRS scoring data indicated that groundwater is contaminated and is used as a drinking water source by more than 10,000 persons. The ROD, however, stated that the groundwater is not contaminated. Sapp Battery, FL. The HRS data stated that groundwater is not contaminated; an ATSDR Health Assessment stated that groundwater contamination is unknown. The ROD indicated that groundwater is contaminated and is used as a source of drinking water by more than 1000 people. Newsom BrotherslOld Reichhold, MS. EPA’s Site Inspection Report revealed potential groundwater contamination. The HRS data stated that the groundwater is used as a source of drinking water by 11,500 persons and no contamination exists. Both the health assessment and ROD, however. reported that the groundwater is contaminated. West Virginia Ordnance, WV. The HRS scoring data stated that the groundwater is used as a source of drinking water by 5000 people and is not contaminated. However. a health assessment and two RODS indicated that the groundwater is contaminated but is not used as a drinking water source 13).
Revised hazard ranking system The Superfund Amendments and Reauthorization Act of 1986 (SARA) required EPA to amend the HRS to more accurately reflect the relative degree of risk to human health and the environment posed by sites in need of evaluation. SARA specified that modifications include the consideration of damage to natural resources that may affect the human food chain, current or potential contamination of ambient air, and current or potential contamination of surface waters used for recreation or as drinking-water supplies. Another primar y requirement is the assignment of a high priority to sites where the release of hazardous substances has resulted in the closing of drinking-water wells or has contaminated a principal drinkingwater supply. The HRS has been revised to include an on-site pathway analysis and more detailed scores for groundwater and surface water pathway analyses. The revised HRS also assigns a higher value to target populations where actual exposures exist (6). Discussion Thus far, the challenge of establishing well-defined priorities for the Superfund program has not been met, and money is being spent with no guarantee that the
program is proviaing aaequate protection of public health and the environment. The decision-making process has reflected an ambiguous approach to using risk assessment as a priority-setting tool, and thus the program suffers from a lack of clear priorities in deciding which sites to clean up. The majority of resources are being directed toward the remediation of sites involving only potential risk, while other sites that involve more urgent health threats may be unaddressed. The effectiveness of the new HRS remains to be seen. Its usefulness as a priority-setting tool will depend largely on the accuracy and comprehensiveness of information used to score sites. Because the new system will not address the hundreds of sites that are already in the pipeline as a result of the old system, a key element of improving the Superfund decision-making process will involve identifying ways to effectively prioritize sites that are currently on the NPL.
References (1)
(2)
(3) (3) (5)
(6)
“Impact Analysis of RCRA Corrective Action and CERCLA Remediation Programs”; Chemical Manufacturers Association: Washington, DC, 1988. “HRS Revisions Support: SARA Studies on HRS Scores and Remedial Actions, HRS Scores and Potential Dangers, and the Effect of the 28.5 Cutoff Score”; U.S. Environmental Protection Agency: Washington, DC, November 1987. “Hazardous Waste Sites and the Rural Poor: A Preliminary Assessment”; Clean Sites, Inc.: Washington, DC, March 1990. Doty. C. B.; Travis, C. C. J . Air Waste Manag. Assoc. 1989, 39(12), 1535-43. “National Priorities List: Final and Proposed Sites, Route Scores”; US.Environmental Protection Agency: Washington. DC. February 1990. Caldwell, S.; Ortiz. A. J . Air Waste Manug. Assoc.. 1989, 39(12), 8 0 1 4 7 .
Carolyn B. Doty is on the research staff at Oak Ridge National Laboratory’s Office of Risk Analysis. She holds B.S. and M . A . degrees from the University of Tennessee. Among other topics, her research concerns hazardous waste policy issues and risk assessment.
Curtis C . Travis is the director of the Office of Risk Analysis at the Oak Ridge, National Laboratory in Oak Ridge, TN. He has a Ph.D. in mathematics from the University of California-Davis.
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continuedfrom p . I777
To improve the system’s reliability, a cyclone was installed between the kiln and the SCC to remove particulates from the gas stream. A wet electrostatic precipitator (WEP) was installed to remove particulates downstream of the SCC, in place of the CHEAF, and a Monarch CPI separator was added to remove the suspended particulate matter in the process water stream. In addition, a Hauptmann conveyor was installed to improve the ram feed system. Selection of the OCS by FWEI was based on its ability to produce low flame temperatures compared to other pure oxygen burners. This allowed the burners to achieve lowered NO, levels, which reduced slagging tendency and the potential for kiln distortion. These modifications proved successful. The feed rate of soils increased from 2000 Ib/h to 4000 lbh. Because of the cyclone and the reduced volume of air, particulate buildup in the SCC was almost eliminated. The WEP proved successful in particulate removal and required little maintenance. Fuel savings of more than 60% were achieved for soil processing during the operation of the improved MIS with the OCS incorporated. Shakedown tests during 1987 revealed that a mist eliminator was required to control particulate emissions, especially for feeds containing high halogen levels. The incineration of materials from the Denney Farm site and other southwest Missouri dioxin sites continued. In addition, a trial bum was made in the summer of 1987 with these objectives: first, to demonstrate the capability of the MIS to simultaneously destroy liquid and solid wastes regulated by both the Toxic Substances Control Act and RCRA; and second, to qualify the MIS to incinerate dioxin-contaminated brominated sludge from southwestern Missouri sites. As a result of the trial bum, the unit was allowed to process brominated sludge. Destruction and removal efficiencies (DREs) exceeding 99.9999% were achieved for PCBs. DREs exceeding 99.99% were demonstrated for hard-to-destroy compounds such as carbon tetrachloride and hexachloroethane. Gopal D. Gupta is a vice-president of Foster Wheeler Enviresponse, Inc. He has a B.S. degree from the Indian Institute of Technology, Kanpur, India, and a Ph.D. from Lehigh University, Bethlehem, PA. He is a registered engineer in New Jersey, has authored more than 80 technical articles, and was an assistant professor in the Department of Mechanical Engineering at Lehigh.
