4.1.2.5 Description of Primary Treatment Technology for Alternative 5, Plasma Torch Alternative 5 consists of excavation and transportation of contaminated soil, sediment, sludge, and solid waste to the CTF for treatment using the plasma torch vitrification technology. Treated wastes could be disposed of in a landfill. The plasma torch vitrification technology is described in this section, along with general support requirements for plasma torch systems. Figures 4-17 and 4-18 present material flow diagrams for Scenario 1 and Scenario 2 respectively. Plasma Torch Plasma torch is a type of electric heating vitrification process. A plasma is an ionized gas used to create extreme heat to melt wastes into a vitrified solid. Retech, Inc., has developed and demonstrated the plasma torch process to the EPA under the SITE program. In addition, Kennedy Van Saun markets, engineers, and constructs a related plasma arc system developed by Electro- Pyrolysis Inc. (HazTECH News 1995). In this related system, unlike the plasma torch system in which the electric arc provides the primary energy for the heating and melting of the target material in a nonoxidizing atmosphere, the plasma functions only as a scrubber for off-gases generated by the electric arc (EPA 1992c). It is believed that the plasma torch technology can be used to destroy organic contaminants and immobilize inorganic contaminants (Environmental Engineering World 1995). Most of these applications have been developed only to bench scale. Retech, Inc., demonstrated a pilot-scale unit under the EPA SITE program and has developed a full-scale unit for treating contaminants in waste. The EPA SITE demonstration evaluated a pilot-scale unit for treating metal-contaminated soil blended with 10 percent diesel oil, zinc oxide, and hexachlorobenzene. The only reported plasma torch operational unit is in Muttenz, Switzerland, and treats hazardous waste. As a result, performance data for the plasma torch technology are limited, and it is still considered an emerging technology. Plasma torch ex situ vitrification thermally converts materials into a glass or glasslike structure and can treat a wide variety of waste streams and contaminants. The most readily available plasma torch vitrification treatment system used is the centrifugal furnace; therefore, this study will assume that wastes will be processed in a centrifugal furnace. Feed material is fed into the furnace. The furnace temperature ranges from 2,200 to 2,900 oF. This extreme temperature is produced by into ionized plasma by passing the gas through an electric arc of direct or alternating current. The gas is accelerated by the electric field colliding with neutral particles at extreme temperatures, causing electrons to be stripped from the gas stream, thus producing plasma. The plasma contacts the feed material and melts it. As the material is continually heated, inorganics remain in the melted material, and organics and metals vaporize and decompose. The molten material cools and begins to harden, thus vitrifying inorganics and other contaminants to a monolithic, nonleachable, vitrified solid. The organic gas is sent to a gas treatment system to remove hazardous constituents. Two plasma torch units at 5.0 tons per hour each can be used to treat the CD wastes. Assuming 24-hour per day operation and a mechanical availability of 70 percent, the plasma torch technology can treat the wastes under Scenario 1 and Scenario 2 in 5.4 years and 8.5 years respectively. Typically, full-scale plasma torch and traditional rotary kiln units measure approximately 8 feet in diameter by 40 feet high. However, a plasma torch unit measuring 10 feet in diameter and 40 feet high is recommended to meet time restraints. The proposed layout in Figure 4-19 is based on demonstration test results; site-specific information; technology capabilities; the Muttenz, Switzerland, treatment unit; and performance results from the EPA SITE program demonstration testing. An overall plasma torch furnace system process flow diagram is shown in Figure 4-20. The three major plasma torch process components include the primary plasma torch chamber, the secondary combustion chamber, and the vapor handling system. A scrubber water treatment system would also be designed and constructed to purify and recycle the water used in the quench and ionizing wet scrubbers. Primary Plasma Torch Chamber The purpose of the plasma heating equipment in the primary plasma torch chamber is to create plasma and heat feed materials. Two plasma torches have been used in full-scale treatment units to provide sufficient heat input. The proposed plasma torch unit also requires two plasma torches to ensure sufficient heating. An operating temperature of 2,200 oF and a residence time at full-flow conditions of 2.5 seconds has been successful in melting soil and destroying organic contaminants. The plasma torch primary chamber may measure approximately 10 feet in diameter and have a total throughput rate of about 5.0 tons per hour. The plasma torch transfers energy to the plasma torch gases, that come in contact with the feed material to increase the gas temperature beyond temperatures normally attainable by chemical reaction. An electric arc is then applied to the materials to increase the gas temperature and vitrify solid constituents of the feed while organic components are volatilized by heat and oxidized by the plasma gas. If sufficient combustion does not occur, additional oxygen can be added to the primary chamber to facilitate organic combustion. A smaller torch can also be directed at the edge of the throat of the primary chamber to ensure that no glass is left on the surface of the rim of the throat after material is discharged. The smaller torch also adds plasma heat to the gases entering the secondary combustion chamber. Secondary Combustion Chamber The combustible materials are transferred to a secondary combustion chamber to continue heating of the feed materials. Additional heat is supplied by natural gas to further incinerate products of incomplete combustion. The off-gases are sent to a comprehensive gas treatment system. Vitrified materials are more manageable than the feed and decrease the probability of contaminant escape into the environment. The vitrified material would be tested to determine whether it can be landfilled. Further treatment would be required if the wastes exceed RCRA standards. Vapor Handling System The vapor handling system consists of quenching, scrubbing, and venting equipment. The vapor handling design is critical for efficiently capturing any potentially hazardous vapors and emissions not combusted in the secondary combustion chamber. A quenching tower cools and condenses the vapors. Scrubbers, filters, or other vapor-liquid separation techniques can be used to remove acid gas, other hazardous gases, and particulates from the gas stream. A slightly caustic scrubber solution has been used to remove or absorb the vapor. The treated liquid should be recycled and can be reused. Scrubber water may contain metal contaminants or particulates volatilized during the treatment process. As a result, appropriate testing and disposal is required for the scrubber water. The venting system consists of an exhaust stack that emits clean gases to the atmosphere. Acid gases, carbon monoxide, carbon dioxide, oxygen, and nitrogen compounds form during the plasma torch treatment of PCBs and are not bound to the vitrified slag. If hazardous compounds are not properly treated by the vapor handling system, further treatment, including nitrogen compound reduction, may be required. Plasma Torch Support Requirements Plasma torch support requirements include site mobilization and access requirements, utilities, contaminated material pretreatment, and residuals post-treatment. A well ventilated, temperature-controlled, enclosed facility would be located at the CTF to implement the plasma torch alternative. The CTF has adequate space for the plasma torch treatment system. A potential general arrangement of the plasma torch technology is presented in Figure 4-19. Preliminary locations of major equipment, feed areas, supplies, and residuals are also shown. Utility requirements include scrubber water, electricity, plasma gas, and air, along with storage facilities for each. These storage facilities include storage tanks for scrubber water and a control center to house electrical equipment. Feed materials with a high moisture content should be dried or dewatered to reduce the amount of moisture before materials are fed to the furnace, thus reducing costs from increased electrical usage. Bulk wastes or 55-gallon drums of contaminated material would be transported to the CTF. Bulk wastes should be pretreated by sorting, size reduction, and screening so that the waste may be fed into the primary plasma torch chamber. The waste material would be melted into vitrified slag in the centrifugal furnace. Construction requirements include foundations for the primary and secondary combustion chambers and scrubbers, buildings to enclose the equipment, and roads. Post-treatment requirements include collection, testing, and transport of the vitrified slag. Scrubber water must also be collected and transported off site to an approved treatment facility.