Figure 4-55: Typical Low temperature Plasma Reactor
The high energy destruction technology is one of many approaches toward
decontaminating of air emissions off-gases prior to atmospheric release. The objective of
the HEC technology is to provide a standalone, field-portable means of treating off-gases
produced during other remedial operations.
The High Energy Corona (HEC) process uses high-voltage electricity to destroy VOCs at
room temperature. The equipment consists of the following: an HEC reactor in which the
VOCs are destroyed; inlet and outlet piping containing process instrumentation to measure
humidity, temperature, pressure, contaminant concentration, and mass flow rate; a means
for controlling inlet flow rates and inlet humidity; and a secondary scrubber.
The HEC reactor is a glass tube filled with glass beads through which the pretreated
contaminated off-gas is passed. Each reactor is 2 inches in diameter, 4 ft long, and
weighs less than 20 pounds. A high voltage electrode is placed along the centerline of the
reactor, and a grounded metal screen is attached to the outer glass surface of the
reactor. A high-voltage power supply is connected across the electrodes to provide 0 to 50
mA of 60-Hz electricity at 30 kV. The electrode current and power depend upon the type and
concentration of contaminant.
The technology is packaged in a self-contained mobile trailer that includes gas
handling equipment and on-line analytical capabilities. Installation consists of
connecting inlet and outlet hoses to the HEC process trailer. Training in the use of the
equipment can usually be accomplished well within 1 hour. Failure control is provided by a
combination of automated and manually activated means, addressing electrical failure, loss
of flow, and loss of VOC containment caused by breakage of the glass reactor vessel. The
HEC process can be operated with little, if any, maintenance required. Neither
catastrophic failure nor any diminishing in levels of performance have been observed
through months of periodic operation in the laboratory. The on-line gas chromatograph and
process instruments do require periodic recalibration to ensure data quality.
Tunable Hybrid Plasma Reactor
Researchers at the Massachusetts Institute of Technology (MIT) are investigating plasma
chemical processes relevant to the development of a versatile mobile versatile mobile
electron-beam driven plasma reactor for efficient on-site decomposition of carbon
tetrachloride (CCl4) and other VOCs. The reactor uses a moderate energy
electron beam (100-300 keV) that is injected into atmospheric air containing the organic
contaminants. The organics are destroyed or oxidized to non-toxic chemicals through their
interaction with the electrons and plasma generated from the electron beam. Since a plasma
is generated, use of either alternating current (AC) or direct current (DC) electric
fields allows a further increase in the electron and gas temperatures to optimize the
treatment process. The high degree of tunability of the reactor gave rise to the name
tunable hybrid plasma (THP) reactor.
Contaminants that can be treated include most or all VOCs and SVOCs. The
potential also exists for treating inorganic compounds, such as oxides of nitrogen and
oxides of sulfur. This technique is specifically useful for destroying organics and
chlorinated solvents such as trichloroethylene (TCE), tetrachloroethylene (PCE), carbon
tetrachloride, chloroform, diesel fuel, and gasoline. Both gas and liquid phase
contaminants are treatable.
The THP technology is best suited for treatment of gaseous
streams with small concentrations of VOCs especially chlorinated compounds.
Continued research and development (R&D) is planned to accomplish the
following: fully characterize the reactor emissions to complete mass balances; adapt the
HEC process to complete real-time control; better understand the physical and chemical
phenomena that make the HEC process work; develop larger reactors; and optimize the
hardware and packaging associated with the technology for specific, as well as modular or
generic, treatment applications.
A detailed discussion of these data elements is provided in Subsection 2.2.3. (Data Requirements for Air
The HEC technology can destroy more than 99.9% TCE. The technology
destroys PCE to a level of 90 to 95%. In preliminary tests with heptane, destruction
levels appear to be extremely high, but have not been quantified. When chlorinated VOCs
are treated, water containing either sodium hydroxide or baking soda is recirculated in a
scrubber to remove acid gases, hydrochloric acid, and chlorine from the reactor effluent.
It should also be noted that further contaminant destruction appears likely in this wet
scrubber. This is presumably because of strong gaseous oxidants that exit the HEC reactor.
Typical outlet properties would be nondetectable concentrations of TCE, ozone,
hydrochloric acid, phosgene, and chlorine, with up to 1 ppmv NOx
(below regulatory limits). Air exits the HEC process at temperatures of 100° C or lower
or slightly above ambient temperature if a wet scrubber is used. A scrub solution
(containing less than 10-wt% sodium chloride in water) is produced when chlorinated VOCs
One reactor processes up to 5 scfm of soil off-gas. The HEC field-scale
process demonstrated at Savannah River uses 21 HEC reactors in parallel to treat up to 105
scfm of contaminated off-gas. A typical application will involve an inlet stream
containing 1,800 ppm of TCE in humid air at 10 to 20° C. Power input is typically 50 to
150 W/scfm being processed. For dry inlet streams, deionized water is added as steam to
produce an inlet humidity (hr) of 60 to 80%. Less than 20 mL per minute of water is
required to humidify a completely dry stream at a flow of 105 scfm. For water-saturated
inlet streams, the stream is preheated (using electric heaters) to lower the hr from 100%
to 80%. In many cases, the vapor-extraction blower associated with retrieving the VOCs
from soil will sufficiently preheat the soil off-gas to 80% or lower so that no further
preheating is required.
Discussions with manufacturers/licensees have been initiated with the belief that HEC
is now ready for commercial availability. The 105-scfm field prototype is available now
for commercial testing and evaluation. Pacific Northwest Laboratory (PNL) is continuing
R&D to improve and scale the technology. Scaleup to 50 scfm per reactor seems feasible
for extremely large applications.
Initial outlay for a 105 scfm process, the prototype field treatment
system, is $50,000. As with any other technology, large-scale production and customization
would significantly reduce costs, perhaps to as low as $20,000. Labor requirements are
projected as 0.25 fulltime equivalent. Energy requirements are $27 per day, or roughly
$0.35 per pound of contaminant. Total cost is roughly $10 per pound of contaminant,
including a 25% contingency to account for any unknown additional costs. Although
maintenance costs are minimal, the total cost figure assumes 8% downtime and a capital
payback period of 6 months.
DOE-RL, 1993. Technology Name: High-Energy Corona,
Technology Information Profile (Rev. 2) for ProTech, DOE ProTech Database, TTP Reference
DOE, 1994. Technology Catalogue, First Edition. February.
TNA-II OTD/OER Crosswalk Worksheet, 1992, "High-Energy Corona for
Destruction of VOCs in Process Off Gases," The 1993 Technology Needs
Crosswalk Report, Vol. 3, Appendix H, TTP Reference No.: RL-3211-01, Richland, WA,
Virden, J.W., W.O. Heath, S.C. Goheen, M.C. Miller, G.M. Mong, and R.L. Richardson,
1992. "High-Energy Corona for Destruction of Volatile Organic Contaminants in
Process Off-Gases," in Proceedings of Spectrum '92 International Topical
Meeting on Nuclear and Hazardous Waste Management, Vol. 2, pp. 670-673, 23-27 August
1992, Boise, ID.
Points of Contact:
General FRTR Agency Contacts
Technology Specific Web Sites:
Government Web Sites
Non Government Web Sites
A list of vendors offering Air
Emission/Off-Gas Treatment is available from EPA
REACH IT which combines information from three established EPA databases,
the Vendor Information System for Innovative Treatment Technologies (VISITT),
the Vendor Field Analytical and Characterization Technologies System (Vendor
FACTS), and the Innovative Treatment Technologies (ITT), to give users access to
comprehensive information about treatment and characterization technologies and
Health and Safety: