On-site remediation of PCB contamination using transportable incineration systems

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<ul><li><p>On-Site Remediation of PCB Contamma tion Using Transportable Incineration Systems </p><p>Nancy Johnson </p><p>Nancy Johnson, P.E., is a project manager in the Treatment Systems Department of Roy F. Weston, Inc. She specialixes in advance plunning/pemritting for Weston transportable incineration systems. </p><p>Many Superfund or hazardous waste sites prove to be excellent candi- dates for remediation using transportable incineration. Transportable incineration has been selected as the alternative of choice to remediate numerous sites throughout the United States. There are a number offirms that provide mobile and transportable incineration equipment and ser- vices. A variety of treatment systems are available, including rotary kilns, fluidized beds, and infrared incinerators. </p><p>Roy F. Weston, Inc., has been instrumental in the development, design, permitting, construction, pe formance testing, and operation of hazardous and toxic waste thermal treatment systems. Weston owns and operates two high-temperature transportable incineration systems (77s~). The first sys- tem is Westons seven-ton-per-hour (tph) l7S-5. The second is the 77s-20, with a design capacity of up to 30 tph. These units are typical rotary kiln incinerators, the most flexible, adaptable type of incineration unit. This article discusses Westons use of these incinerators to remediate soils at sites contaminated with polychlorinated biphenyls (PCBs). </p><p>Although many sites are potential candidates for remediation using transportable incineration, careful evaluation is required to ensure that incineration is a good match for the selected site. Factors such as the volume of soil to be treated, the location of the site, and type of contaminants to be treated must be evaluated to determine whether incineration is a cost-effective remedial option. </p><p>As a rule of thumb, transportable incineration is cost-effective for sites containing more than 1,000 tons of soil. Various fixed costs associated with every site may operate to diminish the cost-effectiveness of using transport- able incineration at smaller sites. The fixed costs are, therefore, an important consideration in the site selection process. The fixed costs generally range from $1 million to $3 million per site and are associated with the following: </p><p>Site preparation Regulatory requirements </p><p>REMEDIATION/SPRING 1994 223 </p></li><li><p>NANCY JOHNSON </p><p>Setup of the unit Demobilization of the system </p><p>Mobilization of the treatment system </p><p>The actual treatment costs for remediating a given site with a transportable incineration system will vary, depending on several factors. The costs of treatment generally range from $150 to $250 per ton, and are dependent on the following variables: </p><p>Contaminant levels Chemical characteristics </p><p>Moisture content </p><p>Media involved (e.g., soil, liquid, sludge) Safety considerations (e.g., unexploded ordnance) </p><p>For example, increased moisture content of the contaminated medium can significantly increase treatment costs because more time and heat are needed to remove the moisture during incineration. </p><p>The nature of the contaminants at a given site will, of course, also affect whether incineration is the most appropriate remedial technology. Al- though incinerators, especially rotary kilns, are very adaptable to waste feed matrices, high-temperature treatment is not applicable for all types of contaminants. For example, although incineration may volatilize heavy metal contaminants, the metals will not be broken down or destroyed. (Metals retained in the ash streams are stabilized to meet toxicity characteristic leaching procedure [TCLPI criteria prior to landfilling.) </p><p>Incineration has recently become a controversial treatment technology. </p><p>REGULATORY APPROVAL Incineration has recently become a controversial treatment technol- </p><p>ogy. Once selected, some degree of concern from the surrounding community can be expected. Effective communication with the public is critical, from the remedial investigation stage through selection of a remedy. This communication generally takes place through public meet- ings, distribution of fact sheets, and community interviews. Implementa- tion of the incineration alternative will proceed much more smoothly if the public feels it has been fully informed and made an active partner in the decision-making process. </p><p>After a record of decision (ROD) or consent agreement is finalized, the design phase can proceed at the sites for which incineration has been selected. During this time, design information is provided to the regulatory agencies and made available for review by the public. A rigorous review is completed by the regulatory agencies. Major areas of concern are the risks of exposure to the site workers and surrounding community. Design conditions are subject to approval prior to operation of the incineration system. </p><p>Following construction and prior to introduction of contaminated soil, public tours of the incineration facility can be conducted. These tours allow the community to see the system u p close and ask questions. </p><p>224 REMEDIATION/!~PRING 1994 </p></li><li><p>ON-SITE REMEDIATION OF PCB CONTAMINATION USING TRANSPORTABLE INCINERATION SYSTEMS </p><p>Openness and cooperative attitudes are eseential to avoiding fear of the unknown. </p><p>An operating approval is generally issued based on successful comple- tion of a performance test or trial burn. During these periods, the incinerator is operated at the maximum anticipated waste feed rate using the operational conditions expected during routine operation. Samples of all influent streams (waste feed) and effluent streams (treated soil, fly ash, scrubber blowdown, and stack gases) are analyzed. To supplement this testing period, ambient air sampling can also be conducted to determine the concentrations of contaminants in the breathing zone of site workers and at the site boundaries. </p><p>Evaluation of the emissions from the incinerator, in conjunction with review of results of ambient air monitoring, allows the regulatory agencies and public to confirm that exposures are within acceptable ranges, as established by the Environmental Protection Agency (EPA). </p><p>Once the incinerator is operational, remote personal computers can be used to allow the public to view the incineration process and remain in contact with on-site activities. A modem link at an easily accessible location, such as a library or school, provides an off-site, real-time, noninteractive window on the process. Openness and cooperative atti- tudes are essential to avoiding fear of the unknown. </p><p>TRANSPORTABLE TREATMENT SYSTEMS Two transportable incineration systems (TISs) with state-of-the-art </p><p>rotary kiln technology are currently being used by Weston to remediate sites contaminated by PCBs and explosives. The first system is the seven- ton-per-hour (tph) TIS-5. The second is the larger TIS-20, with a maximum design capacity of 30 tph. The two systems are discussed below, with particular emphasis on the newer, larger-capacity TIS-20. </p><p>THE TIS-5 In November 1988, Westons TIS-5 was one of the first fully transport- </p><p>able thermal systems to be awarded a Toxic Substances Control Act (TSCA) permit to treat PCB-contaminated soils, liquids, and sediments. In April 1993, the TIS-5 became the first transportable incineration system to be issued a five-year TSCA permit renewal by EPA. Site-specific Resource Conservation and Recovery Act (RCRA) waste disposal approvals were also obtained for the TIS-5. The unit has completed thermal remediation at four sites, is currently operational at a fifth site, and is contracted to begin operations at a sixth site later in 1994. </p><p>At a formal EPA trial burn in January 1992, conducted for an industrial Superfund assignment in Northern Ohio, the TSCA permit for the TIS-5 was expanded to include discrete and concurrent processing of liquid wastes through a liquid injection lance in the kiln. Previous procedures required combining liquids with solid wastes, severely restricting throughput rates, volume, and operating efficiencies for treating liquid waste streams. </p><p>During the test program, the TIS-5 obtained contaminant destruction and removal efficiencies exceeding 99.9999 percent for PCBs and 99.99 percent for other hazardous organic substances. Over a ten-month period on site, the TIS-5 successfully destroyed 290,000 gallons of liquid sludges </p><p>REMEDIATION/SPRING 1994 225 </p></li><li><p>NANCY JOHNSON </p><p>The larger capacity unit...can process more than 20 tons of contaminated soils per hour. </p><p>and oils, 2,600 cubic yards of petroleum and paint sludges, 800 tons of shredded concrete, 4,000 tons of contaminated soils and gravels, and 700 tons of dioxin-laden building debris and soils. </p><p>The unit is transported from site to site on tractor trailers, and takes approximately eight weeks to construct. It operates at a nominal through- put rate of 7 tph and incorporates State-of-the-art emissions controls. Its computerized control system with remote data access by telephone modem enables twenty-four-hour, real-time performance and stack emis- sions tracking by operating personnel, regulatory agencies, and concerned community interests. </p><p>The TIS-5 is now operating at an eight-acre site in the Coal Creek Valley, near Chehalis, Washington, which has been designated a Superfund site by EPA. The site is a former electrical equipment scrap, salvage, and repair facility. The TIS-5 is being used for on-site remediation of 10,000 tons of soils contaminated with PCBs and lead. As necessary, treated soils will be stabilized to meet regulatory criteria for TCLP metals. </p><p>THE TIS-20 The larger capacity unit, the TIS-20, is the second-generation system, </p><p>designed and built to remediate sites with over 20,000 tons of hazardous waste. The unit can process more than 20 tons of contaminated soils per hour. (See Figure 1.) </p><p>Design Improvements Design improvements that enhance on-line availability have been </p><p>incorporated into the second-generation system. These design improve- ments include the following: </p><p>A feed system to prevent buildup of volatile contaminants and to mitigate fugitive emissions. Unique kiln seals designed with graphite seal blocks to prevent any potential fugitive emissions from the kiln. Replacement of kiln fire brick with a combination of insulating fire brick and a phosphate-bonded plastic. This modification reduces unscheduled shutdowns caused by refractory failures (e.g., falling bricks). Use of a cyclone for the kiln exhaust gas to minimize dust entrainment in the gases to the secondary combustion chamber (SCC), resulting in reduced slagging in the downstream equipment. Relocation of the SCC to eliminate hot slag from falling into the wet ash system, thereby preventing steam releases. Two complete and separate fabric filter systems (baghouses) to allow for on-line maintenance. A state-of-the-art continuous emission monitoring (CEM) system, and a user-friendly computerized control and data acquisition system. This system is equipped with real-time modem access for remote monitoring. System is designed for use of oxygen-enriched combustion, </p><p>226 REMEDIATION/SPRING 1994 </p></li><li><p>O N - S ~ REMEDIATION OF PCB CONTAMINATION USING TRANSPORTABLE INCINERATION SYSTEMS </p><p>Area Fuel </p><p>Air Feed Staging </p><p>Area </p><p>. Combuslion </p><p>- I I </p><p>Figure 1. TIS-20 Transportable Thermal Treatment System Process Flow Schematic. </p><p>I I*[ Preparatbn </p><p>Feed System Components The TIS-20 rotary kiln and secondary combustion chamber are </p><p>designed to accommodate a maximum heat release of 100 million British thermal units an hour (Btu/hr). The TIS feed system is composed of three major components: a live-bottom feed hopper, a transfer belt conveyor, and a slinger belt conveyor. (See Figures 2 and 3.) </p><p>The live-bottom hopper is designed with conical metering screws used to control the feed rate into the system. The live-bottom hopper discharges to the transfer belt conveyor. </p><p>The transfer belt conveyor is totally enclosed to prevent fugitive emissions and to contain any material spilling from the belt. Emissions from the enclosure are vented into the kiln for incineration at the burner. The conveyor is equipped with a weigh scale and totalizer to provide feedback to the operator regarding the instantaneous and totalized feed rate to the incinerator. Material on the transfer belt is discharged onto a variable-speed slinget belt conveyor. </p><p>continued on page 2.30 </p><p>REMEDIATION/~PRING 1994 227 </p></li><li><p>NANCY JOHNSON </p><p>228 REMEDIATION/SPIUNG 1994 </p></li><li><p>Fig</p><p>ure </p><p>3. T</p><p>IS-2</p><p>0 T</p><p>rans</p><p>port</p><p>able</p><p> The</p><p>rmal</p><p> Tre</p><p>atm</p><p>ent S</p><p>yste</p><p>m E</p><p>quip</p><p>men</p><p>t Sch</p><p>emat</p><p>ic. </p></li><li><p>NANCY JOHNSON </p><p>The kiln was deaigned with a combination of insulating fire brick and phosphate- bonded plastic refract0 ry... to reduce unscheduled shutdowns caused by catastrophic failures ... </p><p>continued from page 22 7 The variable-speed slinger belt is a high-temperature, high-speed belt </p><p>conveyor designed to throw the material into the rotary kiln. The speed is varied depending on the consistency of the material and the desired discharge distance into the kiln. Below the slinger belt is a spillage screw conveyor to capture material that may stick to the slinger belt or fall off the belt. The collected material is back-conveyed to a container so that it may be re-fed into the rotary kiln. </p><p>Rotary Kiln Design The concurrently fired rotary kiln is designed to process between 4 and </p><p>30 tph of material. The rotary kiln is lined with phosphate-bonded plastic castable with an insulating refractory brick backing. The kiln was designed with a combination of insulating fire brick and phosphate-bonded plastic refractory (instead of only fire brick) to reduce unscheduled shutdowns caused by catastrophic failures (e.g., falling bricks). </p><p>Material Residence Time The material residence time in the rotary kiln (for a given mass feed </p><p>rate) is established by adjusting the rotational speed of the kiln. The nominal speed is 0.5 revolutions per minute (rprn). The maximum rotational speed is 1 .O rpm. The material residence time may be varied from approximately fifteen to sixty minutes. The ash discharging from the rotary kiln is cooled using an immersed wet drag conveyor. </p><p>Discharge Drag Conveyor The discharge drag conveyor consists of a wet bottom drag chain </p><p>conveyor with an integral treated ash quench sump mounted below the treated soil discharge chute of the incinerator. The water in the bottom of the conveyor is used to cool the ash and act as a seal to prevent air from entering the incinerator system. The quenched ash discharges from the treated soil cooling system at approximately 1250 F with a moisture content of approximately 25 percent (by weight). The wet ash can be discharged directly into a collection bin or a series of conveyor belts can be used to transmit the ash into the appropriate treated soil storage bay. Water for cooling is provided from treated scrubber blowdown and makeup water. </p><p>Discharge Gases Discharge gases from the rotary kiln are directed to a cyclone. The </p><p>cyclone removes larger particles from the flue ga...</p></li></ul>