4.1.2.1 Description of Primary Treatment Technology for Alternative 1, High Temperature Thermal Desorption Alternative 1 involves excavation and transportation of 323,000 yd3 of contaminated materials under Scenario 1 or 626,500 yd3 under Scenario 2. Contaminated soil and rock, sediment, sludge, and solid waste would be treated by HTTD at the CTF. Treated wastes would be disposed of in a landfill, and treatment residuals such as condensed oils would be treated off site in a TSCA incinerator. Figures 4-3 and 4-4 present material flow diagrams for Scenario 1 and Scenario 2 respectively. Many thermal desorption systems have been developed to treat wastes at Superfund sites. PRC used available literature and databases such as the Vendor Information System for Innovative Treatment Technologies (VISITT) to identify vendors with HTTD systems that can treat wastes contaminated with PCBs. These vendors indicated that their systems had treated PCB wastes at bench-, pilot-, or full-scale. Table 4-1 presents information concerning operational characteristics of available HTTD systems. Any of these systems may potentially be used to treat PCB-contaminated wastes from the CD sites. For the purpose of this FS, however, PRC has selected the SoilTech ATP Systems, Inc. (SoilTech) and the Rust Remedial Services, Inc. (RUST), X*TRAX systems as representative thermal desorption systems to illustrate how this alternative would be implemented at the site. These systems were selected because they have been used at full scale to remediate Superfund sites contaminated with PCBs. The operation of the SoilTech ATP and RUST X*TRAX systems at the Waukegan Harbor and Resolve Superfund sites, respectively, are discussed below. General HTTD support requirements are also discussed below. SoilTech ATP Systems, Inc., Anaerobic Thermal Processor The ATP technology thermally desorbs (vaporizes) organic compounds such as PCBs from the inert components of solid waste, soil, sediment, and sludge. The SoilTech ATP is a transportable treatment unit used for on-site remediation. It is a commercial plant designed to process 10 tons of waste per hour. SoilTech has also designed a system that can nominally treat 40 tons per hour. Assuming a 70 percent mechanical on-line availability for the 10 ton per hour unit, treatment rates equaling 80 percent of the nominal design treatment rate, and 24 hour-per-day treatment, the ATP would be able to treat the PCB-contaminated soil, sediment, and sludge from the six sites under Scenario 1 in about 6.1 years and 1.5 years, respectively, for the 10- and 40-ton per hour units. Under Scenario 2, treatment would require 8.7 years and 2.2 years, respectively, for the 10- and 40-ton per hour units. Additional time would be required to treat any industrial wastes or MSW that may be amenable to treatment by the ATP. The ATP system consists of the five main process units discussed below. Figure 4-5 shows a process flow diagram of ATP operations. Feed System The ATP feed system consists of two feed hoppers and a conveyor belt. Contaminated solids are introduced from one feed hopper into the preheat zone of the ATP through the conveyor belt. The second feed hopper contains clean sand that is fed to the ATP during startup and shutdown. Sand is also fed to the ATP during normal operations if the waste feed has inadequate inert soil. The sand acts as a heat carrier. Anaerobic Thermal Processor The SoilTech ATP is a proprietary process vessel that uses elevated temperatures to (1) remove volatile and semivolatile contaminants from the contaminated material and (2) isolate and concentrate the contaminants in a liquid phase in the vapor recovery system for proper and permanent disposal. The ATP is a horizontal rotary kiln that contains four separate internal sections: the preheat, retort, combustion, and cooling zones. Figure 4-6 is a simplified sectional diagram showing the four internal zones. The feed enters the ATP through the preheat zone. The preheat zone heats and mixes the feed at temperatures of 400 to 1,000 澹, depending on the contaminant type and concentration, to vaporize materials with relatively low boiling points such as water, volatile organics, and some semivolatile organics. The remaining hot solids pass through a proprietary sand seal that continuously conducts them into the retort zone while almost totally preventing vapor flow. The retort zone operates at temperatures of 1,100 to 1,300 澹, which are high enough to vaporize heavy oils. Thermal cracking of hydrocarbons also takes place in the retort zone, resulting in formation of coke and gases of low molecular weight. The coked and decontaminated solids pass through a second sand seal into the combustion zone. The vapors and gases from the preheat and retort zones are extracted from the ATP under a slight vacuum and enter condensing systems, the two independent condenser trains shown in Figure 4-5. Most of each vapor and gas stream is condensed to liquid water and oils, which are cooled to about 120 澹. The residual vapors, mainly noncondensable gases, are drawn out of the condensing systems and into the combustion zone of the ATP through the stationary end frame. Two auxiliary burners are mounted in the stationary end frame of the ATP. These burners are fired with natural gas and any combustible vapors in the remaining noncondensable off-gas stream to provide process heat. The elevated temperature in the retort zone is achieved by recycling a portion of the hot, decontaminated solids from the combustion zone to the retort zone through a dedicated recycle channel. Conductive heat transfer through the wall of the inner kiln also contributes a minor portion of the heat in the retort zone. The sand seals at both ends of the retort zone maintain a nearly oxygen-free environment that prevents oxidation of hydrocarbons and coke in this zone. The residence time for the solids in the preheat zone is typically about 30 minutes, and the residence time for the solids in the retort zone is 4 to 7 minutes, which is usually long enough to ensure complete volatilization of the hydrocarbons. Samples of treated solids can be collected and analyzed to determine whether the residence time is adequate to remove PCBs. The residence time can be increased by decreasing the waste feed rate. The combustion zone contains a large number of "lifters" in rows around the inner lining of the outer shell. These lifters lift the coked solids and discharge them in sheets that drop vertically through the horizontally moving air and flue gas stream. These falling solids are turbulently exposed to any oxygen present in the air stream, thus allowing combustion of the coke at the same time as the burning of makeup fuels. The combustion zone temperature is maintained at 1,300 to 1,500 澹, depending on the amount of heat required to completely volatilize the contaminants in the retort zone. The solids in the combustion zone that are not diverted for recycling enter the cooling zone. Here they are lifted and distributed to the exterior of the kiln's inner shell to provide conductive heat transfer to the feed in the preheat zone. The treated solids are cooled to an exit temperature of 500 to 600 澹. Finally, the treated solids drop from the ATP annulus into a screw conveyor beneath the sealed, stationary, feed-end plenum. The flue gases exit the top of the plenum and enter the flue gas treatment system. Vapor Recovery System The vapor recovery system cools and condenses water and contaminant vapors removed from the preheat and retort zones of the ATP. The vapors from the preheat zone are withdrawn under a vacuum to a preheat vapor cooling system consisting of a cyclone, condenser, and three-phase separator. The fines collected in the preheat vapor cyclone are returned to the contaminated feed stream just before it enters the ATP. The vapor stream from the retort zone first passes through a pair of cyclones to remove entrained particles. These particles, consisting of dusts and fines, are sent to the combustion zone by a screw conveyor. The vapor is then cooled by oil circulating in two packed columns, the vapor scrubber and the fractionator. These columns act as a two-stage, direct-contact condenser for compounds with relatively high boiling points. For feed that contains little or no heavy oil fraction, a charge of diesel or fuel oil may be added to provide a direct-contact condensing medium. At startup, oils are added to the vapor recovery system to provide circulation and reflux oils. SoilTech has also used circulating water as the cooling medium in the condensing system. The vapor stream from the preheat zone and the uncondensed retort vapors are cooled to near-ambient temperatures in separate, water-cooled condensers. The three immiscible phases exiting each condenser are segregated in a gas-oil-water separator. The final noncondensable gas phase, consisting of light hydrocarbons (mostly butane and lighter compounds) and some inert gases (including carbon dioxide and nitrogen), is recycled to the combustion zone, where the hydrocarbons are oxidized. The liquid hydrocarbon phase in each separator is combined with the condensate from the packed columns. Bottom oil is periodically discharged to a waste oil storage tank. Condensed water is pumped directly to an on-site wastewater treatment system. Flue Gas Treatment System The flue gas treatment system removes particulates and trace hydrocarbons from the flue gas exiting the combustion zone of the ATP. All natural gas fuel and flammable off-gas noncondensable fractions are burned in the combustion zone within the stationary end frame of the ATP. The flue gas is treated in the flue gas treatment system before its release to the atmosphere. The flue gas first passes through a cyclone, which removes coarse dust, and then enters the baghouse, which removes fine dust; the dust collected by the cyclone and baghouse is removed by a screw conveyor and mixed with the treated solids. From the baghouse, the flue gas first passes through an acid gas scrubber to neutralize acid gases and then through an activated carbon unit to remove trace hydrocarbons. The acid gas scrubber may be taken off line and filled with activated carbon to provide additional adsorption capacity in order to improve the treatment system's hydrocarbon removal efficiency. Tailings Handling System The tailings handling system quenches treated solids from the ATP and transports them to a storage pile. The treated solids (tailings) exiting the cooling zone of the ATP are quenched with treated process water and scrubber water, which also serves to control dust. The tailings are then transported to an outside storage pile by screw and belt conveyors. RUST Remedial Services, Inc., X*TRAX System X*TRAX is a patented thermal separation process designed by Chemical Waste Management, Inc. (CWM), to remove organic contaminants from soils, sludges, and other solid media. The X*TRAX process is currently operated by RUST, a subsidiary of CWM. X*TRAX operates at temperatures ranging from 500 to 1,100 澹 to vaporize organic contaminants from solid media. The vaporized contaminants are then condensed and collected as liquids. Although X*TRAX was designed primarily for treating solids contaminated with PCBs, the process can also remove other organic compounds. The X*TRAX Model 200 full-scale system is fully transportable. The system consists of three semitrailers, one control room trailer, eight equipment skids, and various pieces of movable equipment. All skids and trailers that contain liquids have containment curbs for spill control. The X*TRAX Model 200 system has a nominal feed capacity of 5.2 tons per hour at 25 percent moisture. The residence time for solids in the system is approximately 2 hours. Actual feed rates depend on a number of factors such as moisture content, particle size, and other feed characteristics. RUST estimates that the X*TRAX system can achieve feed rates as high as 7.5 tons per hour for some soils that contain 10 percent moisture. Assuming a 70 percent mechanical on-line availability, treatment rates equaling 80 percent of the nominal design treatment rate, and 24 hour-per-day treatment, the X*TRAX system would be able to treat the PCB-contaminated soil, sediment, and sludge from the six CD sites in about 7.5 years under Scenario 1 and 11 years under Scenario 2. The X*TRAX Model 200 system has three main component groups: (1) the thermal separation system, (2) the gas treatment system, and (3) the liquid storage and processing system. In the thermal separation system, contaminated solids are fed into a propane- fired rotary dryer and indirectly heated to a temperature sufficient to volatilize moisture and organic contaminants. The moisture, contaminants, and a small amount of dust are continuously swept from the dryer by nitrogen carrier gas. The carrier gas flows to the gas treatment system, where the moisture, organic contaminants, and dust are removed from the gas stream by scrubbing and condensing processes. These materials are collected in the liquid storage and processing system and separated into excess water, organic liquids, and a solid filter cake. Figure 4-7 shows a simplified material flow diagram for the X*TRAX process. Figure 4-8 shows the equipment layout for the X*TRAX Model 200 and identifies the specific equipment associated with the thermal separation, gas treatment, and liquid storage and processing systems. Each system is discussed below. Thermal Separation System The main function of the X*TRAX thermal separation system is solid materials handling and thermal processing. The thermal separation system consists of a feeder, a rotary dryer, product conveyors, and a product cooler. The feeder includes a hopper and two enclosed conveyors an inclined conveyor and a horizontal conveyor. As shown in Figure 4-8, the feeder is located at one end of the rotary dryer. The feeder is limited to 2.25-inch diameter materials, and contaminated solids are screened to remove larger materials. Feed material is typically delivered to the hopper by a front end loader or similar equipment. The inclined and horizontal conveyors then move the feed material from the hopper to the rotary dryer at a regulated rate. X*TRAX is equipped with an automatic waste feed cutoff feature. When certain monitoring parameters exceed specified control limits, the inclined conveyor automatically shuts down, effectively stopping the flow of contaminated solids to the dryer. The most important component of the X*TRAX system is the rotary dryer. The dryer is a 90- inch diameter, 42-foot long steel cylinder that rotates inside a propane-heated furnace. The dryer is divided into five separate heating zones to enhance temperature control. The dryer is positioned at an incline slightly higher at the inlet. As the dryer rotates, the feed material tumbles slowly to the lower end of the dryer. The propane-heated furnace supplies heat through the dryer wall to vaporize water and organic contaminants from the feed material as it moves through the dryer. Because the heating is indirect, contaminated solids within the dryer are completely isolated from combustion gases in the propane-heated furnace. The dryer operates under a slightly negative pressure, preventing leakage of any waste or waste byproducts. Moisture and organic vapors released from the contaminated solids are continuously swept out of the dryer by nitrogen carrier gas. This gas is maintained at a low oxygen concentration of less than 4 percent to prevent combustion from occurring within the dryer. The primary process control parameter that RUST uses to determine the degree of contaminant removal within the dryer is the treated soil temperature. This parameter is controlled by adjusting the feed rate, furnace temperature, and residence time of materials in the dryer, which is a function of cylinder rotation speed and angle of inclination. Two enclosed screw conveyors move the treated solids from the discharge end of the dryer to the product cooler. The product cooler is a horizontal continuous mixer with a vertical spray tower mounted above the solids inlet. As dry treated solids enter the product cooler, they are sprayed with water to lower their temperature and reduce dust emissions. The solids are also mixed as they pass through the product cooler. The wetted and cooled solids exiting the product cooler drop onto an inclined belt conveyor that carries the material to a soil discharge bin. Gas Treatment System Organic contaminants and water vapors driven from the feed material are transported from the dryer to the gas treatment system by inert nitrogen carrier gas. The gas treatment system removes the moisture and contaminants in the carrier gas and reconditions the gas prior to recycling it back to the dryer. The carrier gas flow rate for the X*TRAX Model 200 is approximately 700 to 900 standard cubic feet per minute (scfm). The primary components of the gas treatment system are an eductor scrubber, primary and secondary condensers, low- and high- temperature reheaters, and a process vent system. The eductor scrubber, the first component of the gas treatment system, is a co-current gas scrubber. The gas enters the top of the scrubber and flows downward through the unit. At the same time, water is sprayed downward at a rate of approximately 120 gallons per minute (gpm) to remove dust particles carried out of the dryer and to cool the gas to 150 to 180 澹. This cooling condenses organic compounds with high boiling points such as PCBs and oils. Water, dust, and organic liquids exiting the scrubber enter a three-phase separator. The scrubbed gas then passes through two condensers in series. The primary condenser is an air-cooled, finned tube heat exchanger that typically cools the carrier gas to near ambient temperature. Most of the water vapor in the carrier gas and organic compounds of low and intermediate volatility are condensed. The resulting liquid flows by gravity to the condensate transfer tank. The carrier gas then passes through a secondary condenser, a shell and tube heat exchanger cooled by a refrigerated mixture of water and ethylene glycol. The carrier gas temperature is reduced to approximately 40 澹 in the secondary condenser, condensing virtually all of the remaining water vapor and organic constituents. A mist eliminator located immediately downstream of the secondary condenser removes any remaining moisture that may be entrained in the gas stream. Liquids from both the secondary condenser and mist eliminator also flow by gravity to the condensate transfer tank. After the removal of organic contaminants and water vapor, the nitrogen carrier gas passes through a low-temperature reheater and a recirculation blower, and then to a propane-fired high- temperature reheater, where the gas temperature is raised to about 600 澹 and is recycled back to the rotary dryer. However, 5 to 10 percent of the carrier gas is continuously discharged to the atmosphere as process vent gas. This venting serves two purposes. First, venting helps maintain a small negative pressure within the X*TRAX system and prevents potentially contaminated gases from leaking out. Second, venting helps maintain a low oxygen concentration within the X*TRAX system of less than 4 percent and eliminates the potential for fire. The vented gas is replaced with nitrogen. The small amount of process vent gas (approximately 30 to 50 scfm) is cleaned as it passes through an air pollution control (APC) system consisting of a 10-micron filter, a high-efficiency particulate air (HEPA) filter, two carbon adsorption beds, and a power vent blower. The filters and carbon adsorption beds have parallel backup units that can be put into service when any APC component becomes spent. Total hydrocarbon concentrations in the process vent gas before and after the first carbon adsorption bed are continuously monitored in the X*TRAX control trailer. This bed is replaced when its removal efficiency falls below 80 percent. The power vent blower forces the treated gas through an approximately 10-foot high stack for discharge to the atmosphere. Liquid Storage and Processing System The liquid storage and processing system for X*TRAX handles materials that the gas treatment system has removed from the carrier gas. Figure 4-7 shows the flow of materials through this system. Materials accumulated in the system are considered treatment residuals and include water, organic liquids, and dust collected by the eductor scrubber, and water and organic liquids collected by the primary and secondary condensers. The components of the liquid storage and processing system include two phase separators; a filter press and three associated tanks; a 600-gallon condensate transfer tank; a 150-gallon organics tank; four 3,000-gallon tanks that handle most of the collected water and organic liquids; and a 1,400-gallon tank that supplies water to the product cooler. The treatment residuals from the liquid storage and processing system include organic liquids, filter cake, and water. Organic liquids, which contain high concentrations of PCBs, are treated and disposed of off site. Because the filter cake may contain high concentrations of organic contaminants such as PCBs, this material is typically blended with feed soil and reprocessed through the rotary dryer. Most of the water in the condensed water tanks is used to wet treated solids in the product cooler. Although this water typically contains low concentrations of organic contaminants, it is pumped through a particle filter and a carbon adsorption bed before transfer to the product cooler supply tank. High Temperature Thermal Desorption Support Requirements HTTD support requirements include site mobilization and access requirements, utilities, contaminated material pretreatment, and residuals post-treatment. HTTD systems typically require a relatively level area ranging from about 5,000 square feet for the Weston LT3 system to 23,000 square feet for the SoilTech ATP system. Additional area is also required for office space, on- site laboratory work, and pretreatment and post-treatment of soil. HTTD systems also require a gravel or concrete pad area and supports such as steel plates, wood, or concrete blocks to support trailers and to prevent equipment from leaning or sliding in soft soil. Site access requirements for HTTD systems are minimal. Most HTTD systems are mobile or transportable. The site must be accessible by tractor trailer trucks of standard size and weight. The roadbed must be able to support vehicles that may deliver the primary desorption chamber, tanks, APC equipment, and other equipment required for system operation. HTTD systems typically require electricity, fuel, and water for cooling, quenching treated soil, and fire protection. HTTD systems may also require compressed nitrogen for purging the primary desorption chamber (for example, the RUST X*TRAXTM system) or for manometers monitoring the oil levels in the condensing units of the vapor recovery system (for example, the SoilTech ATP system). Technology vendors should be contacted for specific utility requirements. Pretreatment requirements typically include size separation and may also include moisture content reduction. Size separation typically includes removing large debris from excavated wastes and screening to remove oversized (greater than 0.5- to 2.5-inch diameter) material. Oversized material may be crushed and treated in the HTTD system or disposed of off site. Extreme care must be taken when screening contaminated materials to ensure that VOCs, asbestos, and metals are not emitted during screening operations. Several methods can be used to reduce soil moisture content. Blending is one option; however, soil blending may be difficult if large amounts of clay or very wet materials are blended. Air drying, preferably in an enclosed tent or building, can be used to dry soil at the CTF. Adequate space must be available on site to allow air drying. Pretreatment for soil moisture content reduction should only be considered if air emissions can be adequately controlled; otherwise, moisture should be removed in the HTTD system at the expense of additional fuel. Post-treatment requirements include treated soil quenching, treatment of inorganics, disposal of treated soil, and treatment residuals disposal. The treated soil is very dry; therefore, soil quenching is needed to reduce emissions of dust contaminated with inorganics. Moisture removed from feed materials can be treated and used as quench water, or else an off-site source of quench water may be provided. Soil quenching should be conducted in an enclosed conveyor at the CTF to reduce dust emissions. Treated soil from the sites may contain high levels of metals and asbestos. Wastes containing inorganics must be treated to immobilize the inorganics before final disposal. Treatment typically involves solidification/stabilization of the treated solids because contaminants in these solids will not be affected by HTTD. The treated soil may be backfilled on site or disposed of off site in a solid or hazardous waste landfill in accordance with ARARs. HTTD systems generate treatment residuals that require off-site treatment. The majority of these residuals are oils or condensed organics generated by the cooling and condensing units of the HTTD system. The condensed organics may be stored in an on-site tank located in the materials handling building in accordance with applicable TSCA and RCRA regulations. The oils and condensed organics can be transported by tanker truck for treatment off site, usually in an approved incinerator. Other solid waste streams such as cyclone and baghouse fines are typically blended with the material to reduce the moisture content of the feed material and to retreat the fines. If the fines meet cleanup goals, they are typically disposed of along with the treated soil.