Thermal
Enhanced Vapor Extraction
System (TEVES)
Description
The
Thermal Enhanced Vapor Extraction System
(TEVES) uses a
combination of soil heating processes (i.e., electrical resistance,
electromagnetic heating, fiber optic/radio frequency heating, or
hot-air/steam
injection) to enhance soil vapor extraction (SVE). It enhances vapor
extraction
by increasing the vapor pressure of semi-volatile organic compounds
and volatile organic
compounds (SVOCs and VOCs,
respectively). It is similar to other methods that heat soil to enhance
soil vapor extraction,
except it uses electromagnetic and radio-frequency heating (RFH) in
combination
with electrical resistance heating.
The
first step of the system is placing three rows of electrodes to a depth
of
approximately 25 feet. As the electrodes begin to heat the soil and
drive off
the soil moisture, electrical conductivity can be maintained by adding
water to
the electrodes. However, electrical heating is self limiting: As the
soil heats
and dries, the current between electrodes stops flowing. At this point,
RFH is
used. RFH uses electromagnetic energy to heat soil to over 300
¡C. RFH enhances
vapor extraction by raising contaminant vapor
pressure and
increasing soil permeability (i.e., drier
soils have
more pore space between particles). Extracted vapor can be treated by a
variety
of technologies, such as granular
activated carbon (GAC).
Limitations
and Concerns
Engineered
barriers to prevent worker exposure to high voltages are recommended.
An
off-gas treatment
system for
contaminated vapors removed from the subsurface needs to be installed.
The
system should be sized to handle peak extraction rates and the mix of
VOCs in
extracted vapor and liquid streams.
The
extraction well should be screened both above and below the target zone
to
ensure sufficient vacuum pressure in the subsurface. This extraction
well
design should also ensure total capture of contaminants released as a result
of the
heating.
The
presence of buried metal objects presents a safety hazard. The
subsurface
should be mapped before the heating system is installed.
Soil
that is tight or has high moisture content has a reduced permeability
to air
and requires more energy to increase vacuum and temperature.
Soil
with highly variable permeability may result in uneven delivery of
airflow to
the contaminated regions.
Soil
that has a high organic content results in reduced removal rates
because of sorbed VOCs.
As
with SVE, remediation projects using TEVES are highly dependent upon
the
specific soil and chemical properties of the contaminated media.
A
potential explosion hazard exists from concentrated fumes released from
the
vacuum unit.
Applicability
The
system is designed to treat and remove SVOCs and VOCs from soil.
Technology
Development Status
This
technology is commercially available.
Web
Links
http://www.sandia.gov/Subsurface/factshts/ert/teves.pdf
http://www.frtr.gov/matrix2/section4/4-9.html
Other
resources
See
related descriptions of Soil
Vapor
Extraction,
Six-Phase
Soil Heating,
and Dynamic
Underground Stripping.
Also
see http://www.clu-in.org/download/citizens/insitutherm.pdf.