A thermal blanket is a device used in thermal desorption to clean
soil contamination
Soil contamination, soil pollution, or land pollution as a part of land degradation is caused by the presence of xenobiotic (human-made) chemicals or other alteration in the natural soil environment. It is typically caused by industrial activity ...
. The primary function of a thermal blanket is to heat the soil to the boiling point of the contaminants (usually 100 to 325 °C and as high as 900 °C
) so that they break down. A vacuum pulls the resulting gas (along with volatilized contaminants) into a separate air cleaner that may use various methods, such as
carbon filters and high-heat ovens, to completely destroy the contaminants. Aside from evaporation and volatilization, the contaminants may also be removed from the soil through other mechanisms such as
steam distillation
Steam distillation is a separation process that consists in distilling water together with other volatile and non-volatile components. The steam from the boiling water carries the vapor of the volatiles to a condenser; both are cooled and ret ...
,
pyrolysis
The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...
,
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
, and other
chemical reaction
A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...
s.
Due to their placement, the thermal blanket can only be used in shallow areas, which is around 1 meter. The process can take more than 24 hours to treat 6 inches of soil and up to 4 days for contaminated areas with depths of 12 to 18 inches.
Deep contamination (contamination at depths greater than 1 meter) is handled using a similar method but with a deep penetrating heat source. This is commonly referred to as an
in situ thermal desorption (ISTD) thermal well and it uses heater elements that consist of
nichrome
Nichrome (also known as NiCr, nickel-chromium or chromium-nickel) is a family of alloys of nickel, chromium, and often iron (and possibly other elements) commonly used as resistance wire, heating elements in devices like toasters, electrical kettl ...
wires in a ceramic insulator. Like the thermal blankets, the heating temperature could reach as high as 900 °C, heating adjacent regions through heat conduction.
Vacuum is also applied to withdraw broken contaminants.
Concerns
It is reported that the application of the thermal blanket is limited
and this could be attributed to a number of concerns. For example, as a contaminant becomes heated, it may leak outside of the area of the thermal blanket. Therefore, the blanket must completely cover the contaminated area and have a strong enough vacuum to prohibit the spread of contamination. Incomplete destruction of contaminants may also lead to the introduction of
dioxins
Dioxin may refer to:
* 1,2-Dioxin or 1,4-Dioxin, two unsaturated heterocyclic 6-membered rings where two carbon atoms have been replaced by oxygen atoms, giving the molecular formula C4H4O2
*Dibenzo-1,4-dioxin, the parent compound also known as ...
and
furans
Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as furans.
Furan is a colorless, flammable, highly ...
into the air.
The thermal blanket method has not been effectively tested on organic contaminants. The technology is presently commercially available.
Shell
Shell may refer to:
Architecture and design
* Shell (structure), a thin structure
** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses
** Thin-shell structure
Science Biology
* Seashell, a hard ou ...
Technology Ventures, Inc., for instance, has developed its own ISTD thermal blanket solution that can treat or remove contaminants on near-surface soil or pavements without excavation.
See also
*
Soil contamination
Soil contamination, soil pollution, or land pollution as a part of land degradation is caused by the presence of xenobiotic (human-made) chemicals or other alteration in the natural soil environment. It is typically caused by industrial activity ...
References
*
External links
A description of thermal blankets
{{DEFAULTSORT:Thermal Blanket
Environmental soil science