TerraTherm offers low, moderate,
and higher temperature applications of Thermal
Conduction Heating (TCH). As incorporated within TerraTherm’s
proprietary In Situ Thermal Desorption (ISTD)
technology, TCH has been applied to sites worldwide since 1989.
What is Thermal Conduction?
Thermal conduction is the process of heat flowing from the hot end of a solid object (like an iron rod) to the cold end. In soil or rock, heat flows from TerraTherm’s heater wells out into the formation by grain-to-grain contact (in soil) and across solid objects (rocks). The fluids (water, air, NAPL) in contact with the solids also heat up at the same time. The heat moves out radially from each thermal well until the heat fronts overlap.
TerraTherm installs a series of patented electrically-powered heaters and vapor extraction points in situ, to heat contaminated soil to target treatment temperatures. Target treatment temperatures are typically 100°C for volatile contaminants and between 150°C and 325°C for semi-volatile contaminants.
Benefits of TCH
Thermal conductivity values for the entire range of known soils vary by a factor of less than plus or minus three, while fluid conductivity of soils may vary by a factor of a million or more. Compared to fluid injection processes, the conductive heating process is uniform in its vertical and horizontal sweep. Transport of the vaporized contaminants is further improved by the creation of permeability, which results from drying (and, if clay is present, shrinking) of the soil close to the heaters. Preferential flow paths are created even in tight silt and clay layers, allowing flow and capture of the vaporized contaminants. TCH produces uniform heat transfer through thermal conduction and convection in the bulk of the soil volume. This allows the achievement of very high contaminant removal efficiency with a nearly 100% sweep efficiency, leaving no area untreated.
TCH can be applied at low
(~100°C), and higher
(>100°C) temperature levels to accomplish the remediation
of a wide variety of contaminants, both above and below the water
TCH is the only major in situ thermal remediation technology capable of achieving target treatment temperatures above the boiling point of water.
TCH is effective at virtually any depth in almost any media.
TCH works in tight soils, clay layers, and soils with wide heterogeneity in permeability or moisture content that are impacted by a broad range of volatile and semi-volatile contaminants, such as:
- Explosives Residue
- Chlorinated Solvents
- Heavy Hydrocarbons
Applicable to Both In Situ and Stockpiled Soils and Sediments
The TCH technology can be utilized to heat in situ soils and stockpiled soils and sediments. The design of the treatment system for in situ soils (ISTD) typically includes vertically installed heaters whereas the design of the treatment system for the stockpiled soils (In-Pile Thermal Desorption, or IPTD) typically incorporates horizontally installed heaters. Examples of the elements of each system are shown below:
TCH Application Using Vertical Heater Wells
(Click to enlarge)
TCH Application Using Horizontal Heater Wells
(Click to enlarge)
The TCH technology can operate inside, beneath, and near buildings and infrastructure. This capability has been field proven at numerous projects.
The TCH technology can be applied to contaminants in soils both above and below the water table (see also Permeability and Geology) where the soils can be heated up to target treatment temperatures. Contaminants such as TCE, PCE, and other VOCs that have boiling points similar to water can be treated simply by steam distillation. Contaminants such as PAHs, dioxins, PCBs, and other SVOCs that have higher boiling points than water are treated by boiling off the water within the treatment zone, and then by heating the soil to the designated treatment temperatures. Where significant groundwater flow is present, additional measures such as groundwater management or a hydraulic barrier may be required. TerraTherm has successfully used steam injection into the high-K zones to augment the ISTD process, thereby ensuring complete heat-up and treatment of both tight zones and permeable zones