Remediation Technologies Screening Matrix, Version 4.0 4.25 Thermal Desorption
(Ex Situ Soil Remediation Technology)
  Description Synonyms Applicability Limitations Site Information Points of Contact
Data Needs Performance Cost References Vendor Info. Health & Safety
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>>3.6 Ex Situ Thermal Treatment (assuming excavation)

      >>4.25 Thermal Desorption
Introduction>> 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.

Description:

Figure 4-25a: Typical High Temperature Thermal Desorption Process
Figure 4-25b: Typical Low Temperature Thermal Desorption Process

 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.

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Synonyms:

DSERTS Code: N12 (Thermal Desorption).  Low Temperature Thermal Desorption (LTTD).

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Applicability:

Thermal desorption systems have varying degrees of effectiveness against the full spectrum of organic contaminants.

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.

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Limitations:

Factors that may limit the applicability and effectiveness of the process include:
  • 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.

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Data Needs:

A detailed discussion of these data elements is provided in Subsection 2.2.1 (Data Requirements for Soil, Sediment, and Sludge). In addition to identifying soil contaminants and their concentrations, information necessary for engineering thermal systems to specific applications include soil moisture content and classification, determination of boiling points for various compounds to be removed, and treatability tests to determine the efficiency of thermal desorption for removing various contaminants at various temperatures and residence times. A sieve analysis is needed to determine the dust loading in the system to properly design and size the air pollution control equipment.

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Performance Data:

Most of the hardware components for thermal desorption systems are readily available off the shelf. All ex situ soil thermal treatment systems employ similar feed systems consisting of a screening device to separate and remove materials greater than 5 centimeters (2 inches), a belt conveyor to move the screened soil from the screen to the first thermal treatment chamber, and a weight belt to measure soil mass. Occasionally, augers are used rather than belt conveyors, but either type of system requires daily maintenance and is subject to failures that shut the system down. Soil conveyors in large systems seem more prone to failure than those in smaller systems. Size reduction equipment can be incorporated into the feed system, but its installation is usually avoided to minimize shutdown as a result of equipment failure.

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.

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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.

SOIL TECHNOLOGY:

Thermal Desorption

 

 

 

RACER PARAMETERS

Scenario A

Scenario B

Scenario C

Scenario D

Small Site

Large Site

Easy

Difficult

Easy

Difficult

 

 

 

 

 

COST PER CUBIC FOOT

$2

$7

$1

$3

COST PER CUBIC METER

$81

$252

$44

$110

COST PER CUBIC YARD

$75

$232

$40

$101

Detailed Cost Estimate 

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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.

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

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

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.

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Site Information:

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Points of Contact:

General FRTR Agency Contacts

Technology Specific Web Sites:

Government Web Sites

Non Government Web Sites

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Vendor Information:

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.

Government Disclaimer

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Health and Safety:

Hazard Analysis

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