IN-SITU THERMAL DESORPTION
In-situ Thermal Desorption (ISTD) is an in-situ conductive thermal process used to heat the target zone to around the boiling point of water. During this process, water and vapour are extracted through a SVE system to maintain hydraulic and pneumatic control, and to remove the contaminants of concern (CoCs) mobilised by the heating through vaporisation and extraction in the vapour phase. Provectus is the sole UK licensee of Terratherm Technology developed and proven on numerous sites in the USA.
The process utilises conductive heating and vacuum to remediate the impacted strata by applying heat and vacuum simultaneously to the materials in the impacted zone using an array of vertical heaters nested around SVE abstraction wells. Each heater well contains an electrically powered heating element inserted into a protective casing within each well, which has an operating temperature of approximately 600-800°c. Heat flows through the matrix from each nest of heating elements primarily by thermal conduction, resulting in uniform heat propagation – thermal conductivity is nearly invariant over a wide range of rock types.
As the temperature of the strata rises both CoCs and pore waters containing CoC are effectively boiled off into the vapour phase. Vapours are collected continuously using centrally located SVE abstraction wells and associated heat exchangers/ off-gas GAC treatment prior to discharge to atmosphere.
ISTD soil remediation technology can successfully treat soils impacted with a wide range of volatile and semi-volatile contaminants including DNAPLs, LNAPLs, PCBs, dioxins, pesticides, chlorinated solvents, tars, PAHs, explosives residues and mercury.
An important feature of the ISTD thermal conduction heating process is the small range of variance in thermal conductivity for the entire range of soil values. Heat flow through the soil formation is not generally limited by soil type, heterogeneity, or other factors that typically limit the effectiveness of remedial technologies that rely solely on flow of fluids through the soil matrix.
ISTD treats contaminated soils in place and as no soil is excavated, on-site workers and neighbours are not exposed to the odours, noise, dust and vehicle movements often associated with traditional “dig and dump” projects.
ISTD treatment can be successfully utilised where traditional SVE treatments would fail and a typical ISTD project reduces timescales by up to 70% when compared with traditional SVE treatments, at which time the soil contaminants have been reduced to negligible levels.