Thermal desorption systems are designed to remove organic compounds from solid matrices such as soil, sludge, filter cake, or drill cuttings without thermally destroying them. It is a separation technology, not a destruction technology. Thermal desorption units should not be confused with incinerators.
Thermal Desorption: Capabilities and Limitations
Thermal desorption has successfully been used for just about every organic contaminant found to date. This does not mean that thermal desorption is the best choice for every contaminated soil project. With the exception of mercury, thermal desorption cannot be used to remove heavy metals. However; stabilizing agents can be added to the treated soil prior to discharge to decrease the leachability of most metals.
Thermal desorption units can mechanically treat most any moisture level, but at higher moistures the cost can become prohibitive. Excessive moisture in the feed soil should be avoided when possible. As an example, a small direct fired system that could process 15 tons per hour with 10% moisture in the feed would drop to 10.5 tons per hour if the moisture increased to 18%. This 30% decrease in process rate results in a 40% increase in the treatment cost per ton. For most projects, if the feed material contains more than 25% moisture dewatering or drying options should be investigated.
Since it is a thermal process, there is a common belief that temperature is the only significant parameter to monitor. While it is true that better removal efficiencies are usually achieved at higher temperatures, other factors must be considered. Since the process is governed by mass transfer, heating time and the amount of mixing are also key parameters in optimizing removal efficiency.