LTTD Treatment Technology and Information

LTTD, or Low Temperature 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 (i.e., air emission) treatment system. The design of an LTTD system aims to volatize contaminants, while attempting not to thermally oxidize them.

Two common LTTD designs are the rotary dryer (fig1) and thermal screw. Rotary dryers are horizontal cylinders that can be indirect or direct-fired. The dryer is normally inclined and rotated. For the 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.

Figure 1 - Rotary Dryer

Low Temperature Thermal Desorption

Based on the operating temperature of the desorber, thermal desorption processes can be categorized into two groups:

Low temperature thermal desorption or LTTD, and high temperature thermal desorption or HTTD. It is important to note that thermal desorption completed at lower temperatures does not to destroy organics.

In low temperature thermal desorption, wastes are heated to between 90 and 320 °C (200 to 600 °F). it is most often used for remediating fuels in soil. Unless heated to the higher end of the 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 or HTTD, wastes are heated to 320 to 560 °C (600 to 1,000 °F). HTTD is frequently used in combination with incineration, solidification/stabilization, or dechlorination, depending upon site-specific conditions.