Thermal Enhanced Vapor Extraction System (TEVES)
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.
The system is designed to treat and remove SVOCs and VOCs from soil.
Technology Development Status
This technology is commercially available.