Public Services and Procurement Canada
High temperature thermal desorption (HTTD) is a process where excavated contaminated materials are heated from 315 0C to 540 0C (600 to 1,000 0F) in a chamber to volatilize water, organic contaminants and certain metals. The higher temperatures used in this process facilitate removal of semi-volatile organic compounds (SVOCs) (<0.01 mm Hg vapor pressure). A gas or vacuum system transports the vaporized water and contaminants to an air emission treatment system, where particulates and contaminants are removed. In contrast to incinerating, the operating temperatures and residence times in a thermal desorption system are designed to volatilize selected contaminants, without oxidizing them. Thermal desorption treatment is not designed to destroy organics.
Treatment of a contaminated soil using a thermal desorption system requires excavation and transportation of the soil to the reactor, were it is heated to a pre-determined temperature. Two common thermal desorption reactor designs are the rotary dryer and the thermal screw. Rotary dryers are horizontal or inclined cylinders that can be indirectly or directly fired.. In thermal screw units, screw conveyors or hollow augers are used to transport the soil through an enclosed trough. Hot oil or steam circulates through the auger to indirectly heat the soil. These units may be transported to the contaminated site.
Treatability tests are recommended to determine the efficiency of thermal desorption for removing various contaminants at various temperatures and residence times.
Control and treatment of air emissions from thermal desorption operations is an extremely important consideration. There should be no emission of metals, polycyclic aromatic hydrocarbons (PAHs) or dioxins/furans from the system.
Application examples are available at these addresses:
This technology is capable of reducing final contaminant concentrations to below 5 mg/kg for target compounds (CPEO , 2002). HTTD costs in Canada are competitive with landfills or biological treatment (CSMWG, 2005).
Composed by:Josée Thibodeau, M.Sc National Research Council
Latest update provided by:Martin Désilets, B.Sc. National Research Council
Updated Date: March-07-19