Description:

 Thermal desorption is a physical separation process and is not designed to destroy organics. Wastes are heated to volatilize water and organic contaminants. A carrier gas or vacuum system transports volatilized water and organics to the gas treatment system. The bed temperatures and residence times designed into these systems will volatilize selected contaminants but will typically not oxidize them.

Two common thermal desorption designs are the rotary dryer 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 medium through an enclosed trough. Hot oil or steam circulates through the auger to indirectly heat the medium. All thermal desorption systems require treatment of the off-gas to remove particulates and contaminants. Particulates are removed by conventional particulate removal equipment, such as wet scrubbers or fabric filters. Contaminants are removed through condensation followed by carbon adsorption, or they are destroyed in a secondary combustion chamber or a catalytic oxidizer. Most of these units are transportable.

Three types of thermal desorption are available and briefly described as following:

1. Direct Fired: Fire is applied directly upon the surface of contaminated media. The main purpose of the fire is to desorb contaminants from the soil though some contaminants may be thermally oxidized.
2. Indirect Fired: A direct-fired rotary dryer heats an air stream which, by direct contact, desorbs water and organic contaminants from the soil. The Low Temperature Thermal Aeration (LTTA^®) developed by Canonie Environmental Services Corporation is a good example of indirect fired system which has been successfully used to remove DDT family compounds from soil.
3. Indirect Heated: An externally fired rotary dryer volatilizes the water and organics from the contaminated media into an inert carrier gas stream. The carrier gas is later treated to remove or recover the contaminants. XTRAX™ thermal Desorption System is a process using indirect heated desorption followed by a high-energy scrubber gas treatment, which successfully removed >99% of PCB from contaminated soil.

Based on the operating temperature of the desorber, thermal desorption processes can be categorized into two groups: high temperature thermal desorption (HTTD) and low temperature thermal desorption (LTTD).

High Temperature Thermal Desorption (HTTD)

HTTD is a full-scale technology in which 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. The technology has proven it can produce a final contaminant concentration level below 5 mg/kg for the target contaminants identified.

Low Temperature Thermal Desorption (LTTD)

In LTTD, wastes are heated to between 90 and 320 °C (200 to 600 °F). LTTD is a full-scale technology that has been proven successful for remediating petroleum hydrocarbon contamination in all types of soil. Contaminant destruction efficiencies in the afterburners of these units are greater than 95%. The same equipment could probably meet stricter requirements with minor modifications, if necessary. Decontaminated soil retains its physical properties. Unless being 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.

Synonyms:

Applicability:

The target contaminant groups for LTTD systems are nonhalogenated VOCs and fuels. The technology can be used to treat SVOCs at reduced effectiveness.

The target contaminants for HTTD are SVOCs, PAHs, PCBs, and pesticides; however, VOCs and fuels also may be treated, but treatment may be less cost-effective. Volatile metals may be removed by HTTD systems. The presence of chlorine can affect the volatilization of some metals, such as lead. The process is applicable for the separation of organics from refinery wastes, coal tar wastes, wood-treating wastes, creosote-contaminated soils, hydrocarbon-contaminated soils, mixed (radioactive and hazardous) wastes, synthetic rubber processing waste, pesticides and paint wastes.

Limitations:

• There are specific particle size and materials handling requirements that can impact applicability or cost at specific sites.
• Dewatering may be necessary to achieve acceptable soil moisture content levels.
• Highly abrasive feed potentially can damage the processor unit.
• Heavy metals in the feed may produce a treated solid residue that requires stabilization.
• Clay and silty soils and high humic content soils increase reaction time as a result of binding of contaminants.

Data Needs:

Performance Data:

Many vendors offer LTTD units mounted on a single trailer. Soil throughput rates are typically 13 to 18 metric tons (15 to 20 tons) per hour for sandy soils and less than 6 metric tons (7 tons) per hour for clay soils when more than 10% of the material passes a 200-mesh screen. Units with capacities ranging from 23 to 46 metric tons (25 to 50 tons) per hour require four or five trailers for transport and 2 days for setup.

The time to complete cleanup of the "standard" 18,200-metric ton (20,000-ton) site using HTTD is just over 4 months.

Soil storage piles and feed equipment are generally covered as protection from rain to minimize soil moisture content and material handling problems. Soils and sediments with water contents greater than 20 to 25% may require the installation of a dryer in the feed system to increase the throughput of the desorber and to facilitate the conveying of the feed to the desorber. Some volatilization of contaminants occurs in the dryer, and the gases are routed to a thermal treatment chamber.

Cost:

The key cost driver information and cost analysis was developed in 2006 using the Remedial Action Cost Engineering and Requirements (RACER) software.

Key Cost Drivers 

·        Economy of Scale

o       Quantity of material treated has a large impact

·        Moisture content

o       Increases required heat input (increasing fuel costs)

Cost Analysis

The following table represents estimated costs (by common unit of measure) to apply thermal desorption technology at sites of varying size and complexity.   A more detailed cost estimate table which includes specific site characteristics and significant cost elements that contributed to the final costs can be viewed by clicking on the link below.

Detailed Cost Estimate 

References:

A Citizen's Guide to Thermal Desorption (English Version) 2001.

A Process Description of Terra Therm's Thermal Desorption Process.

Treatment Technologies for Site Cleanup: Annual Status Report (ASR), Tenth Edition, EPA 542-R-01-004

Innovative Remediation Technologies:  Field Scale Demonstration Project in North America, 2nd Edition

Remediation Technology Cost Compendium - Year 2000

Treatment Experiences at RCRA Corrective Actions, December 2000, EPA 542-F-00-020

Abstracts of Remediation Case Studies, Volume 4,  June, 2000, EPA 542-R-00-006

Guide to Documenting and Managing Cost and Performance Information for Remediation Projects - Revised Version, October, 1998, EPA 542-B-98-007

Anderson, W.C., 1993. Innovative Site Remediation Technology Thermal Desorption, American Academy of Environmental Engineers.

California Base Closure Environmental Committee (CBCEC), 1994. Treatment Technologies Applications Matrix for Base Closure Activities, Revision 1, Technology Matching Process Action Team, November, 1994.

EPA, 1988. Shirco Infrared Incineration, EPA RREL, series includes Technology Evaluation Peake Oil, EPA/540/5-88/002a; Technology Evaluation Rose Township, EPA/540/5-89/007a; Technology Evaluation Rose Township Vol. II, EPA/540/5-89/007b, PB89-167910; Applications Analysis, EPA/540/S5-89/010; Technology Demonstration Summary, EPA/540/S5-89/007; Demonstration Bulletin, EPA/540/M5-88/002; and Technology Evaluation Report Peake Oil Vol. II, EPA/540/5-88/002B, PB89-116024.

EPA, 1989. American Combustion Oxygen Enhanced Incineration, EPA RREL, series includes Technology Evaluation, EPA/540/5-89/008; Applications Analysis, EPA/540/A5-89/008; Technology Demonstration Summary, EPA/540/S5-89/008; and Demonstration Bulletin, EPA/540/M5-89/008.

EPA, 1992. A Citizen's Guide to Thermal Desorption, EPA, OSWER, Washington, DC, EPA/542/F-92/006.

EPA, 1992. Low Temperature Thermal Treatment (LT3 ) System, Demonstration Bulletin, Washington, DC, EPA/540/MR-92/019.

EPA, 1992. Ogden Circulating Bed Combustor McCall Superfund Site, EPA RREL, Technology Evaluation, EPA/540/R-92/001; and Demonstration Bulletin, EPA/540/MR-92/001.

EPA, 1992. Roy F. Weston, Inc. Low Temperature Thermal Treatment (LT3) System, EPA RREL, Demonstration Bulletin, EPA/540/MR-92/019; and Applications Analysis, EPA/540/AR-92/019.

EPA, 1993. Low Temperature Thermal Aeration (LTTA) System, Canonie Environmental Services, Inc., EPA RREL, Demonstration Bulletin, EPA/540/MR-93/504.

EPA, 1993. X-TRAX Model 100 Thermal Desorption System Chemical Waste Management, EPA RREL, Demonstration Bulletin, EPA/540/MR-93/502.

EPA, 1994. Thermal Desorption System, Clean Berkshires, Inc., EPA RREL, Demonstration Bulletin, EPA/540/MR-94/507; and Capsule, EPA/540/R-94/507a.

EPA, 1994. Thermal Desorption Treatment, Engineering Bulletin, EPA/540/5-94/501.

EPA, 1994. Thermal Desorption Unit, Eco Logic International, Inc., EPA RREL, Demonstration Bulletin, EPA/540/MR-94/504.

EPA, 1997. Best Management Practices (BMPs) for Soil Treatment Technologies: Suggested Operational Guidelines to Prevent Cross-media Transfer of Contaminants During Clean-UP Activities, EPA OSWER, EPA/530/R-97/007.

Federal Remediation Technologies Roundtable, 1995. Remediation Case Studies: Thermal Desorption, Soil Washing, and In Situ Vitrification, EPA/542/R-95/005.

• Thermal Desorption at the Anderson Development Company Superfund Site, Adrian, Michigan
• Thermal Desorption at the McKin Company Superfund Site, Gray, Maine
• Thermal Desorption at the Pristine, Inc. Superfund Site, Reading, Ohio (Complete Cost and Performance Report,PDF Version)
• Thermal Desorption at the T H Agriculture & Nutrition Company Superfund Site, Albany, Georgia
• Thermal Desorption/Dehalogenation at the Wide Beach Development Superfund Site, Brant, New York

Federal Remediation Technologies Roundtable, 1998. Remediation Case Studies: Ex Situ Soil Treatment Technologies (Bioremediation, Solvent Extraction, Thermal Desorption), EPA/542/R-98/011

• Vacuum-enhanced, Low Temperature Thermal Desorption at the FCX Washington Superfund Site, Washington, North Carolina
• Thermal Desorption at the Solvent Refined Coal Pilot Plant, Fort Lewis, Washington
• Thermal Desorption at Naval Air Station Cecil Field, Site 17, OU 2, Jacksonville, Florida
• Thermal Desorption at the Outboard Marine Corporation Superfund Site, Waukegan, Illinois
• Thermal Desorption at the Port Moller Radio Relay Station, Port Moller, Alaska
• Thermal Desorption at the Re-Solve, Inc. Superfund Site, North Dartmouth, Massachusetts
• Thermal Desorption at the Waldick Aerospace Devices Superfund Site, Wall Township, New Jersey

Federal Remediation Technologies Roundtable, 1998. Remediation Case Studies: In Situ Soil Treatment Technologies (Soil Vapor Extraction, Thermal Processes), EPA/542/R-98/012

• In Situ Thermal Desorption at the Missouri Electric Works Superfund Site, Cape Girardeau, Missouri

Johnson, N.P., J.W. Noland, and P.J. Marks, 1987. Bench-Scale Investigation of Low Temperature Thermal Stripping of Volatile Organic Compounds From Various Soil Types: Technical Report, AMXTH-TE-CR-87124, USATHAMA.

Lighty, J., et al., 1987. The Cleanup of Contaminated Soil by Thermal Desorption, Presented at Second International Conference on New Frontiers for Hazardous Waste Management, EPA Report EPA/600/9-87/018.

Marks, P.J. and J.W. Noland, 1986. Economic Evaluation of Low Temperature Thermal Stripping of Volatile Organic Compounds from Soil, Technical Report, AMXTH-TE-CR-86085, USATHAMA.

McDevitt, N.P., J.W. Noland, and P.J. Marks, 1986. Bench-Scale Investigation of Air Stripping of Volatile Organic Compounds from Soil: Technical Report, AMXTH-TE-CR-86092, USATHAMA.

U.S. Army, August 1990. The Low Temperature Thermal Stripping Process, USATHAMA, APG, MD, USATHAMA Cir. 200-1-5.

• EPA Remedial Action: McKin, ME
• EPA Remedial Action: Otteti & Goss, NH
• EPA Remedial Action: Outboard Marina, Waukegan Harbor (OU 3), IL
• EPA Remedial Action: Cannon Engineering/ MA
• EPA Removal Action: Drexler RAMCOR, WA
• EPA Demo: ReSolve, Inc., Superfund Site, MA
• EPA Demo: Wide Beach Development Superfund Site, NY & Outboard Marine Corp., IL
• EPA Demo: Niagara-Mohawk Power Co., NY
• EPA Demo: Pesticide Site, AZ
• Army Demo: Letterkenny Army Depot, PA
• EPA & Army Demo: Tinker AFB, OK & Anderson Development Co. Superfund Site, MI
• EPA SITE Demo: EPA Combustion Research Facility, Jefferson, AK
• Alaskan Battery Enterprises Superfund Site, Fairbanks, AK
• Escambia Wood Treating Company, Superfund Site, Pensacola, FL
• Pristine, Inc., Reading, OH
• T H Agriculture & Nutrition Company Superfund Site, Albany, GA
• Anderson Development Company Superfund Site, Adrian, MI
• McKin Company Superfund Site, Gray, ME
• Port Moller Radio Relay Station, Port Moller, AK
• FCX Washington Superfund Site, Washington, NC
• The Solvent Refined Coal Pilot Plant, Fort Lewis, WA
• Naval Air Station Cecil Field, Site 17, OU 2, Jacksonville, FL
• Outboard Marine Corporation Superfund Site, Waukegan, IL
• The Re-Solve, Inc. Superfund Site, North Dartmouth, MA
• Waldick Aerospace Devices Superfund Site, Wall Township, NJ
• Missouri Electric Works Superfund Site, Cape Girardeau, MO
• 

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A list of vendors offering Ex Situ Thermal Soil Treatment is available from  EPA REACH IT which combines information from three established EPA databases, the Vendor Information System for Innovative Treatment Technologies (VISITT), the Vendor Field Analytical and Characterization Technologies System (Vendor FACTS), and the Innovative Treatment Technologies (ITT), to give users access to comprehensive information about treatment and characterization technologies and their applications.

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