Fact Sheets

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What is Thermal Desorption

Spring 2004                                                      Fact Sheet 2004-02

Thermal Desorption

Thermal Desorption is a process used to remove contaminants from the soil. Temperatures between 500 to 1,100 degrees Fahrenheit (°F) are used to physically separate moisture and contaminants from the soil. The exhaust created by this process is collected by an air pollution control system and heated to temperatures of approximately 2000°F to destroy the contaminants. The exhaust is then filtered to remove any remaining dust particles from the air stream.

Cleaned soil and air are discharged from the treatment system. Tests on the soil treated by Thermal Desorption systems typically show a reduction in contamination to below detectable concentrations. Soil not treated to acceptable levels is returned to the system and retreated to achieve required cleanup parameters.

How it Works

Thermal Desorption

The Thermal Desorption system uses heat to separate contaminants from the soil and then thermally destroys them.

Once rocks and other debris are removed, the soil is fed into the primary treatment unit. Inside this rotating drum, soil is heated to between 500 and 1,100°F (775°F is the optimum temperature for soils at Camp Edwards.) These temperatures dry the soil, burn off any organic material and drive off contaminants from the soil, so that they are caught in the exhaust or off-gas.

The continuous tumbling ensures all of the soil is exposed to the heat for the appropriate time period. While contaminants are captured in the off-gas, treated soil is discharged from the primary treatment unit and rehydrated with clean water to reduce the soil temperature and control dust emissions.

Treatment of the contaminants continues as the off-gas flows through the air pollution control system. As it spins through the cyclone, the soil particles caught in the off-gas are removed before the off-gas moves into the thermal oxidizer. Using temperatures of up to 2,000°F the oxidizer destroys any remaining contaminants, transforming them into nitrogen, water and carbon dioxide.

In the quench or cooling chamber, clean water is used to cool the off-gas to a temperature that can be handled by the filtering system.

The air pollution control system then uses air filters to pull any remaining treated particles of soil out of the air. A sonic pulse is used to periodically disengage the collected particles from the filter and deposit them in the treated soil stream. The filtered offgas is then discharged.

An air permit, issued by the Massachusetts Department of Environmental Protection will ensure all emissions meet state requirements.

Discharged soil is sampled to confirm that treatment is effective. Once sample results confirm that cleanup goals have been met, soil cleaned through this process can be used for fill in site restoration.

Proven Process

The Thermal Desorption system has been proven to successfully treat soil contaminated by explosives chemicals similar to those found at Camp Edwards. In a similar use at the Kansas Army Ammunition Plant, the Thermal Desorption system removed explosives chemicals, including RDX, HMX and TNT to levels below what can be detected by approved U.S. Environmental Protection Agency (EPA) laboratory methods. Similar results were seen at the Iowa Army Ammunition Plant.

Thermal Desorption unit at Demolition Area 1

Treatability Study for Camp Edwards

To address soil contamination at Camp Edwards, a a Treatability Study was conducted to determine the ability of the Thermal Desorption system to remove perchlorate from soil. Perchlorate is a water- soluble salt, used as an oxidizer in munitions and solid fuels for rockets and missiles. It also is used in, fireworks, safety flares, airbags and other items. It has been found in soil and groundwater at Camp Edwards.

The study conclusively verified that Thermal Desorption successfully treated perchlorate to levels below what can be detected using approved EPA laboratory methods.

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