Thermal Desorption (Low Temperature Thermal Desorption LTTD)
Type of treatment:
Treatment
Description:
Thermal desorption separates contaminants from soil. Soil is heated in a chamber in which water, organic contaminants and certain metals are vaporized. A gas or vacuum system transports vaporized water and contaminants to an off-gas treatment system (the design of a system aims to volatize contaminants, while attempting not to oxidize them; otherwise, thermal desorption would be another way of saying incinerator). It is important to note that thermal desorption does not destroy organic compounds.
Based on the operating temperature, this process is categorized into two groups.
In Low Temperature Thermal Desorption (LTTD), wastes are heated to between 90° and 320°C. LTTD is most often used for remediating fuels in soil. Unless heated to the higher end of the LTTD temperature range, organic components in the soil are not damaged, which enables treated soil to retain the ability to support future biological activity.
In High Temperature Thermal Desorption (HTTD), wastes are heated to 320° to 560 °C. HTTD is not used for oil/ fuel contaminated soil treatment.
:
Polluted soil, sand and often small pebble (e.g. no larger than 5cm).
:
Equipment can be imported and installed.
:
Very effective in reducing concentrations of petroleum products including gasoline, jet fuels, kerosene, diesel fuel, heating oils, and lubricating oils.
:
• Applicable to constituents that are volatile at operating temperatures.
:
Requires personnel and expertise to operate, site, waste transport and handling equipment.
· Treatment of the off-gas must remove particulates and contaminants.
· Dewatering may be necessary to achieve acceptable soil moisture content levels.
· Technique developed for soil remediation (not accidental pollution treatment), applicability for OSW depends on the characteristics and on the hydrocarbon content of the waste.
· THC concentration should be maximum 3% (except for systems operating in an inert atmosphere e.g. thermal screw). System is not suited for high concentrations of oil in waste (e.g. 20 to 30%).
· Due to the low temperature used, it is probable that weathered oil generally recovered on beach will not be treated (would require higher temperature to evaporate).
:
Minimal, if the vaporized hydrocarbons are correctly treated in a secondary treatment unit: afterburner, catalytic oxidation chamber (which destroys the organic constituents), condenser, or carbon adsorption unit (which trap organic compounds for subsequent treatment or disposal) prior to discharge to the atmosphere.
:
Refer to incineration and atmospheric releases legislation.
Special authorisation may be required for such work.
:
· Rapid treatment time; most commercial systems capable of over 25 tons/ hr throughput. Thermal screw: up to 15 tons/ hr.
· Can consistently reduce THC to below 10 ppm and BTEX below 100 ppb (and sometimes lower).
:
Total cost of treatment for one m3 ranges from 40 to 200 euros / ton (Source: Bocard).
Typical cost for oily waste treatment is approx. 150 euros (Source: Cedre).
