PLASMA ARC TECHNOLOGY
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| Overview: | 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 eductor located in the pollution abatement portion of the
system. |
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| Compliance Benefit: | PAT
is used to destroy hazardous wastes. The destruction process renders the
waste non-hazardous while reducing its volume. The destruction of hazardous
waste helps facilities meet the requirements of waste reduction under RCRA,
40 CFR 262, and may also help facilities reduce their generator status
and lessen the regulatory burden (e.g., recordkeeping, reporting, inspections,
transportation, accumulation time, emergency prevention and preparedness,
and emergency response) under RCRA, 40 CFR 262.
The Compliance Benefits
listed here are only meant to be used as a general guideline and are not
meant to be strictly interpreted. Actual Compliance Benefits will vary
depending on the factors involved, e.g., the amount of workload involved. |
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| Materials Compatibility: | No materials compatibility issues were identified. |
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| Safety and Health: | Caution
must be exercised with the equipment, as high voltages are a potential danger.
The process employs two plasma torches, each of which are capable of a sustained
output of 160 kW. The torches must be shielded and protected.
Since the process is use to treat hazardous and combustible materials, proper personal protective equipment must be worn and other safety practices must be employed. Consult your local industrial health specialist and your local health and safety personnel prior to implementing this technology. The PAT waste treatment
process has several safety advantages when compared to conventional incineration
systems. The primary advantage is the use of less air for combustion.
Water-cooled chambers allow better sealing, which reduces the risk of
uncontrolled releases of noxious fumes. Water cooling reduces the exterior
surface temperature, which reduces burn and fire hazards. It also allows
for faster shutdown, and a significant thermal capacitance for responding
to unusual events. Rapid cooling and capture of the reaction products
in the slag or in the off-gas treatment systems reduces the opportunities
for operator contact with the hazardous materials. |
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| Benefits: |
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| Disadvantages: |
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| Economic Analysis: | The
National Defense Center for Environmental Excellence (NDCEE), which is operated
by Concurrent Technologies Corporation (CTC), was tasked by the Department
of Defense (DOD) to evaluate the applicability of PAT to treat complex military
wastes. This evaluation included a life-cycle cost analysis, using CTC's
ECAMSM program, conducted in 1997.
Since the PACT-2
was designed as a research unit, its operating costs are higher than if
it was a full-time processing system. For this reason, a transportable
PACT-5 system, a PACT-8 single torch system, and a PACT-8 also were evaluated
to provide an end user configuration for processing waste materials. |
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| Assumptions: |
Table 1. Operating Costs Per Ton for Wastes Studied
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| NSNs: | None
Identified. |
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| Approving Authority: | Approval
is controlled locally, and the technology should be implemented only after
engineering approval has been granted. |
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| Points of Contact: | Dr.
Mahmood A. Qazi Concurrent Technologies Corporation 100 CTC Drive, Johnstown, PA 15904 Phone: (814) 269-2726 |
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| Vendor: | Retech,
Inc. A Division of M-4 Environmental 100 Henry Station Road Ukiah, CA 95482 Plasma Energy Applied
Technology Corporation Georgia Institute
of Technology Plasma Technology
Corporation Plasma Technology,
Inc. These vendors may not represent a complete list, as there may be other suppliers of this type of equipment. |
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| Source(s): | Concurrent
Technologies Corporation. Plasma Arc Technology Evaluation. Science and
Technical Report. Draft. April 28, 1997. |
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| Supplement(s) to the Data Sheet: |
Schematic of the plasma arc technology.
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