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 educator located in the pollution abatement
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| Compliance Benefit: | PACT 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 general guidelines 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. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 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, your local health and safety personnel, and the appropriate MSDS 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.
Consult your local industrial health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing this technology. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 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, was tasked by the
Department of Defense 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 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. Assumptions:
Table 1. Operating Costs Per Ton for Wastes Studied
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| NSN/MSDS: | None
Identified.
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| Approving Authority: | Appropriate authority for making process changes should always be sought and obtained prior to procuring or implementing any of the technology identified herein.
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| Points of Contact: | For more information | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Vendors: | This is not meant to be a complete list, as there may be
other suppliers of this type of equipment.
Retech,
Inc. Plasma Energy Applied
Technology Corporation Georgia Institute of
Technology Plasma Technology
Corporation Plasma Technology,
Inc. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Sources: | Concurrent Technologies Corporation. Plasma Arc Technology
Evaluation. Science and Technical Report. Draft. April 28, 1997.
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| Supplemental: |
Schematic of the plasma arc technology.
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