Thermal desorption is an environmental remediation technology that utilizes heat to increase the volatility of contaminants such that they can be removed (separated) from the solid matrix (typically soil, sludge or filter cake).
Thermal desorption first appeared as an environmental treatment technology in 1985 when it was specified in the Record of Decision for the McKin Company Superfund site within the Royal River watershed in Maine.
An early direct fired thermal desorption project was the treatment of 8000 tons of toxaphene (a chlorinated pesticide) contaminated sandy soil at the S&S Flying Services site in Marianna Florida in 1990, with later projects exceeding 170,000 tons at the Cape Fear coal tar site in 1999.
A status report from the United States Environmental Protection Agency shows that thermal desorption has been used at 69 Superfund sites through FY2000.
Thermal desorption is a widely accepted technology that provides a permanent solution at an economically competitive cost.
The world’s first large-scale thermal desorption for treatment of mercury-containing wastes was erected in Wölsau, for the remediation of the Chemical Factory Marktredwitz (founded in 1788) was considered to be the oldest in Germany.
Most indirect fired rotary systems use an inclined rotating metallic cylinder to heat the feed material.
The majority of these systems utilize a secondary combustion chamber (afterburner) or catalytic oxidizer to thermally destroy the volatilized organics.
Some systems use electric resistance heaters instead of a heat transfer media and may employ a single auger in each housing.
One can only guess that capital and/or energy costs have prevented the development of a microwave thermal desorber at the commercial scale.
In addition to managing the volatilized components, the particulate solids (dust) that exit the desorber must also be removed from the offgas.
In essence 20,000 tons of contaminated soil could be reduced to less than one tank truck of extracted liquid residue for off-site disposal.
Desorbers using offgas destruction systems use combustion to thermally destroy the volatilized organics components forming CO, CO2, NOx, SOx and HCl.
Regardless of the name, the destruction unit is used to thermally destroy the hazardous organic constituents that were removed (volatilized) from the soil or waste.