The plasma arc technology (PAT) uses heat generated by a plasma arc to melt the inorganic portion of waste material while destroying the organic portion. Types of waste materials tested include medical incinerator ash, Longhorn sludge, open burning ground soil, agricultural and plastic/glass blast media, surrogate absorbent materials, Mendocino soil spiked with dichlorobenzene, and waste paint.

Several demonstration tests were performed in a Plasma Arc Centrifugal Treatment (PACT) system designed and built by Retech, Inc., Ukiah, California, specifically for pilot-scale testing. The heart of the PACT-2 system is its primary combustion chamber, which consists of a 2-foot diameter centrifuge (i.e., a tub) heated by a RP-75 T plasma torch fitted with a 200 kW power supply. Typically the chamber gas temperature ranges between 927-1200°C (1700-2200°F), and the temperature of the molten material is approximately 1650°C (3000°F). The primary chamber operates under a slight vacuum.

The waste is fed into the primary chamber from an Archimedes screw-type feeder. The feeder is approximately 152-cm (5-ft) long, 51 cm (20 in) in diameter with 7.6-cm (3-in) high flights. The feeder drops the waste onto an auger screw-type feeder, which introduces the waste to the tub through a port in the chamber wall. For proper feeding to the auger feeder, material size is limited to approximately a 1-in cube of solid, dense material.

Once the tub reaches its capacity, feeding is stopped and a dwell time of approximately 30 minutes is maintained. The molten material is drained by slowing the tub rotation speed, allowing the material to flow through a hole in the bottom center of the tub. The material is cast into a steel slag mold, which rotates with the tub. To remove the mold, tub rotation is stopped. The PACT-2 system is equipped with an automatic mold alignment mechanism that allows a slag mold manipulator to lift the mold, move it to the slag mold chamber, and then pull it out of the chamber into the work area. The mold manipulator is enclosed in the slag mold chamber, which has an isolation valve that keeps solid material or gases from entering during processing. The valve also allows the primary chamber to remain hot while the slag mold is changed. Once an empty mold is put in place, the system can be restarted and processing of waste can resume.

Process gases exit the primary chamber through a port in the chamber wall. These gases enter the secondary combustion chamber, which is heated by an RP-250N plasma torch. The temperature range is the same as the primary combustion chamber. A 2-second residence time is maintained to ensure complete destruction of the hazardous organic compounds. Off gases are pulled through the system by a venturi educator located in the pollution abatement portion of the system.

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