Contaminants using Smart Burners
With thermal desorption all organic contaminants can be treated, as all these chemicals will vaporise at a given temperature and can be extracted from the surface for further treatment. Here is a ist of he most common pollutants found in soils and treated by thermal desorption (incl. Smart Burners )
PCB (polychlorinated biphenyls)
& PIP (persistent inorganic pollutant)
Trichloro-1 1 1-ethane
The pure organic contaminants (only hydrogen and carbon) will not only be desorbed, but also be completely oxidized in the combustion chamber. There will be no other release into the atmosphere than CO2 and H2O.
Halogenated Hydrocarbons: PCB, Dioxins, Furans, Pesticides
The principle of desorption remains the same for halogenated hydrocarbons (chlorinated solvents, PCB, dioxins, furans, pesticides, etc.), i.e. that they will evaporate and be collected in the gas phase (their boiling points are all well below 550°C). Once oxidized, the halogens will remain in the gas phase and therefore a secondary gas treatment is required before release into the atmosphere.
The boiling point of chlorinated solvents is below 100°C, so the target temperature of the soil can even be below. This implies that these chemicals can also be treated in (ground)water.
Regarding the treatable inorganics, such as cyanides and mercury, their behaviour is very specific. Cyanides are desorbing easily (depending on the complexes, the boiling temperatures varies from 300°C to 420°C) and are oxidized to CO2 and NOx in the burner’s flame. In order to not exceed the limit values the exhaust gas composition needs to be followed carefully; otherwise a secondary treatment is required.
Although obviously heavy metals cannot be treated thermally, mercury is a particular case. It can be desorbed as nearly all forms of mercury have boiling points well below 550°C. However, the off-gas cannot be oxidized. Therefore mercury impacted materials require special attention and a dedicated unit.
Off gas treatment
Combustion of off-gas
In all cases, hydrocarbons are volatilized during a thermal desorption process (the Smart Burners Technology process) and, as gases, they are conveyed to a combustion chamber where they are oxidized to CO2 and H2O, with a generation of energy.
In some cases hydrocarbons may contain other elements, like sulphur or chlorine, which are not oxidized to CO2 and H2O and need additional gas treatment in order not to exceed the emission standards set for the release of clean gasses into the atmosphere. Standard methods like condensation and the use of activated carbon are applied here.