• Eliminates moisture from the unsaturated zone, increasing soil permeability.
• Desorbs volatile and semi-volatile compounds.
• Creates substantial permeabilities in silt and clay, which boosts desorption up to a
certain point, in zones with the lowest permeability.
• Destroys in situ pollutants by oxidation or pyrolysis at temperatures of around
400
C (Baker and Kuhlman 2002; Hiester et al. 2013).
• TCH process is flexible.
Treating groundwater with TCH can involve heat loss related to water flow.
These losses can be partially limited by specifically considering the role of the
extraction and water reinjection wells (downstream wells and reinjection upstream,
or the converse, depending on the hydrogeological context). Additionally, the
energy required with TCH is very high (90–220 kWhÁm
À3 ) (Lemming et al. 2010).
3.4.2 Steam-Enhanced Extraction
Steam-enhanced extraction (SEE) occurs by injecting vapor to extract organic
compounds. This technique has been used for oil recovery. The main techniques
used consist in: (1) letting the heat from the injected steam soak the oil by
maintaining the pressure of the steam in the well and, (2) driving the oil to the
wells (steam drive or steam flooding) using vapor circulation as a heat transferring
agent (White and Moss 1983). The environmental applications for vapor injection
are mainly based on the second approach (U.S. Army Corps of Engineers 2014).
SEE consists in injecting steam (generated on-site by fuel oil or gas combustion in
a boiler) into the pollution source through injection wells to heat the soils, and
mobilize and evaporate the pollutants. These pollutants are then extracted by the
negative pressure exerted in the extraction wells before being treated on-site. Steam
injections into the unsaturated zones are meant to create a pressure gradient (like soil
vapor extraction) to increase vapor pressure, reduce product viscosity and consequently, increase the recovery level of pollutants in gaseous form (Davis 1998;
Kingston et al. 2010).
Steam can be injected into unsaturated and saturated zones (Aines et al. 1995;
Davis 1998; Heron et al. 2002). Figure 3.13 illustrates SEE in the vadose zone.
The phenomena caused by vapor injection are chronologically as follows (Davis
1998; Kingston et al. 2014; Stewart and Udell 1988; Udell 1996; Wu 1977):
• Steam injection will push the cold water underground.
• The vapor will condense and transfer heat to the medium and move the resulting
hot water.
• The steam will displace once the soil temperature is in equilibrium with the steam
temperature, which will again push the cold water and the bank of condensed
steam (hot water).
Therefore, polluted zones will be subject to three phenomena:
3 In Situ Thermal Treatments and Enhancements: Theory and Case Study
179
• Desorbs volatile and semi-volatile compounds.
• Creates substantial permeabilities in silt and clay, which boosts desorption up to a
certain point, in zones with the lowest permeability.
• Destroys in situ pollutants by oxidation or pyrolysis at temperatures of around
400
C (Baker and Kuhlman 2002; Hiester et al. 2013).
• TCH process is flexible.
Treating groundwater with TCH can involve heat loss related to water flow.
These losses can be partially limited by specifically considering the role of the
extraction and water reinjection wells (downstream wells and reinjection upstream,
or the converse, depending on the hydrogeological context). Additionally, the
energy required with TCH is very high (90–220 kWhÁm
À3 ) (Lemming et al. 2010).
3.4.2 Steam-Enhanced Extraction
Steam-enhanced extraction (SEE) occurs by injecting vapor to extract organic
compounds. This technique has been used for oil recovery. The main techniques
used consist in: (1) letting the heat from the injected steam soak the oil by
maintaining the pressure of the steam in the well and, (2) driving the oil to the
wells (steam drive or steam flooding) using vapor circulation as a heat transferring
agent (White and Moss 1983). The environmental applications for vapor injection
are mainly based on the second approach (U.S. Army Corps of Engineers 2014).
SEE consists in injecting steam (generated on-site by fuel oil or gas combustion in
a boiler) into the pollution source through injection wells to heat the soils, and
mobilize and evaporate the pollutants. These pollutants are then extracted by the
negative pressure exerted in the extraction wells before being treated on-site. Steam
injections into the unsaturated zones are meant to create a pressure gradient (like soil
vapor extraction) to increase vapor pressure, reduce product viscosity and consequently, increase the recovery level of pollutants in gaseous form (Davis 1998;
Kingston et al. 2010).
Steam can be injected into unsaturated and saturated zones (Aines et al. 1995;
Davis 1998; Heron et al. 2002). Figure 3.13 illustrates SEE in the vadose zone.
The phenomena caused by vapor injection are chronologically as follows (Davis
1998; Kingston et al. 2014; Stewart and Udell 1988; Udell 1996; Wu 1977):
• Steam injection will push the cold water underground.
• The vapor will condense and transfer heat to the medium and move the resulting
hot water.
• The steam will displace once the soil temperature is in equilibrium with the steam
temperature, which will again push the cold water and the bank of condensed
steam (hot water).
Therefore, polluted zones will be subject to three phenomena:
3 In Situ Thermal Treatments and Enhancements: Theory and Case Study
179