United States
Environmental Protection
Agency
Off ice of
Solid Waste and
Emergency Response
EPA/542/F-92/006
March 1992
&EPA
A Citizen's Guide to
Thermal Desorption
Technology Innovation Office
.Technology Fact Sheet
Page
CONTENTS
What Is Thermal
Desorpfion?
How Doe* Thermal
Desorption Work?
Why Consider Thermal
Desorption? 3
Will It Work At Every
Site? 3
Where Is Thermal
Desorption Being
Selected? 3
For More Information
What Is Thermal
Desorption?
Thermal desorption is an innovative
treatment technology that treats soils
contaminated with hazardous wastes by
healing the soil at relatively low
temperatures (200-1000°F) so that
contaminants with low boiling points
will vaporize (turn into gas) and,
consequently, separate from the soil.
(The other soil contaminants, if any, are
treated by other methods.) The
vaporized contaminants are collected
and treated, typically by an air
emissions treatment system.
Thermal desorption is a different
treatment process than incineration.
Thermal desorption uses heat to
physically separate the contaminants
from the soil, which then require further
treatment Incineration uses heat to
actually destroy the contaminants.
How Does Thermal
Desorption Work?
Thermal desorption makes use of either
in situ or ex situ processes. In situ - in
place -- treats soils without excavating
them. Ex situ treats excavated soils.
There are three steps in thermal
desorption: 1) heating the soil to
vaporize the contaminants; 2) treating
the vaporized contaminants; and 3)
testing the treated soil. There are four
different methods for heating the soil to
vaporize the contaminants:
• In situ steam extraction
Direct heating
Indirect heating
Oxygen free heating
See Figure 1 on page 2 for an
illustration of in situ steam extraction.
Figure 2 on page 2 shows the processes
that require excavation: direct heating,
indirect heating, and oxygen free
heating.
?. Ubroiy (Pl.
„ ......... ..., ..... .._ ...... ____
Thermal Desorption Profile g*** /f
Heats soil at relatively low temperatures to vaporize contaminants and remove them.
f, I2thFlo>r
Is most effective at treating volatile organic compounds, semlvolatile organic compounds and other
organic contaminants, such as porychlorlnated blphenyls (PCBs), and polyaromatlc hydrocarbons
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Figure 1
In Situ Steam Extraction
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A variety of factors determine which heating method will be
used, including soil type and amount, contaminant type and
amount, and cost. Each of the four heating methods are
briefly described below:
In situ (in place) steam extraction (Figure 1, above) - the
soil is kept in place, and hot steam is pumped through the
ground. The volatile contaminants vaporize and are
collected in a vacuum. A disadvantage to this heating
method is that a limited area of soil is treated at one time.
Contaminants are, therefore, removed at a slower rate.
Direct heating (Figure 2, below) - the soil is excavated and
put into a treatment vessel. The treatment vessel is heated
and the heat is transferred to the soil. As the contaminants
become heated they vaporize. The advantage of this heating
method is that it is simple and cost effective to set up.
Indirect heating (Figure 2, below) - the soil is excavated
and put into a treatment vessel. A burner is tnuisported to
the site, which heats an air source. The heated air is
pumped into the treatment vessel by a blower. The air heats
the soil, which causes the contaminants to vaporize. This
heating method requires more fuel because some heat is lost
during transfer.
Figure 2
Three Ex Situ Thermal Desorption Methods
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Oxygen free (Figure 2, page 2) - the soil is placed in a
treatment vessel which has no oxygen and which is sealed
and filled with nitrogen to avoid any contact between the
soil and oxygen. The outside of the vessel is heated, and the
contaminants vaporize.
Once vaporized, the contaminants can be treated in the same
manner regardless of the heating method. The vaporized
contaminants are either: 1) cooled and condensed into a
liquid, which is then placed in drums for treatment or
disposal; or 2) trapped in carbon filters which are then
treated or disposed of; or 3) burned in an afterburner. All
disposals must meet Federal, State, and local standards. The
selection of the vapor treatment system depends on the
concentration of the contaminants, cleanup standards, and
various economic and engineering considerations.
The performance of thermal desorption is typically
measured by comparing the contaminant levels in treated
soils with those of untreated soils. With the ex situ
processes, if the treated soil is nonhazardous, it is
redeposited on-site or taken elsewhere as backfill. If,
however, the soil requires further treatment (for example,
there are additional contaminants that do not respond to this
process), it may be treated with another technology or
transported off-site for disposal.
Why Consider Thermal Oesorption?
Thermal desorption can effectively reduce hazards to both
people and the environment. Thermal desorption is most
successful in treating soils, sediments, and sludges that are
contaminated with volatile organic compounds, semivolatile
organic compounds, polychlorinated biphenyls (PCBs), and
some polyaromatic hydrocarbons (PAHs). The equipment
available is capable of treating up to 10 tons of
contaminated soil per hour. Finally, the low temperatures
require less fuel than other treatment methods.
Will It Work At Every Site?
Thermal desorption does not work well on all types of soil.
If the soil is wet, water will vaporize along with the
contaminants. Because of the additional substance (water)
being vaporized, more fuel is required to vaporize all the
contaminants in the wet soil. Soils with high silt and clay
content are also more difficult to treat with thermal
desorption. When heated, silt and clay emit dust, which can
disrupt the air emission equipment used to treat the
vaporized contaminants. In addition, tightly packed soil
often does not permit the heat to make contact with all of
the contaminants. It is, therefore, difficult for them to
vaporize. Finally, thermal desorption has limited
effectiveness in treating contaminants such as heavy metals,
since they do not separate easily from the soil, and strong
acids, since they can corrode the treatment equipment.
Where Is Thermal Desorption Being
Selected?
Thermal desorption has been selected as a treatment method
at numerous Superfund sites. For example, thermal
desorption was used at the Cannon Engineering Corporation
site in Plymouth, Massachusetts to treat soil contaminated
with volatile organic compounds and semivolatile organic
compounds. Thermal desorption effectively treated 11,330
tons of contaminated soil at the site. The process began in
May 1990 and was completed five months later in October
1990. With this technology, cleanup goals for the site were
met and exceeded. In addition, the property was restored so
that, once again, it can be put to commercial or industrial
use. Table 1 on the following page lists some additional
Superfund sites where thermal desorption has been selected
or used, their locations, and the types of facilities requiring
treatment
What is An innovative
Treatment Technology?
Treatment technologies are processes
applied to the treatment of hazardous
waste or contaminated materials to
permanently alter their condition
through chemical, biological, or
physical means. Technologies that
have been tested, selected or used for
treatment of hazardous waste or
contaminated materials but lack well-
documented cost and performance
data under a variety of operating
conditions are called innovative
treatment technologies.
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Table 1
Super-fund Sites Where Thermal Desorptlon Has Been Used or Selected
Site
Cannon Engineering
McKin
Ottati and Goss
RE-Solve
American Thermostat
University of Minnesota
Martin Marietta
Caldwell Trucking
Claremont Polychemical
Fulton Terminals
Marathon Battery
Metaltec/Aerosystems
Reich Farms
Sarney Farm
Waldick Aerospace Devices
Wamchem
Outboard Marine/
Waukegan Harbor
Location
Massachusetts
Maine
New Hampshire
Massachusetts
New York
Minnesota
Colorado
New Jersey
New York
New York
New York
New Jersey
New Jersey
New York
New Jersey
South Carolina
Illinois
Types of Facilities*
Chemical waste handling, storage, and incineration
Waste storage, transfer, disposal
Drum reconditioning
Chemical reclamation
Industrial manufacturing of thermostats
University wastes (PCBs)
Aerospace equipment manufacturer
Unpermitted septic waste
Chemical
Former waste tank farm
Former battery manufacturer
Metal manufacturing
Uncontrolled waste disposal
Industrial and municipal landfill
Manufacturing and electroplating of plane parts
Former dye manufacturing plant
Marine products manufacturing
'All waste types and site conditions are not similar. Each site must be individually investigated and tested. Engineer-
ing and scientific judgment must be used to determine if a technology is appropriate for a site.
For More Information
EPA prepared this fact sheet to provide basic information on thermal desorptlon. Additional technical
reports listed below may be obtained by calling (513) 569-7562 or writing to:
Center for Environmental Research Information
26 West Martin Luther King Drive
Cincinnati, OH 45268
There may be a charge for these documents.
• U.S. Environmental Protection Agency, 1990. In Situ Steam/Hot Air Stripping, Toxic Treatment, Inc.,
EPA/540/M5-90/003.
U.S. Environmental Protection Agency, 1990. Inventory of Treatabillty Study Vendors, Volume 1,
EPA/540/2-90/0038.
U.S. Environmental Protection Agency, 1990. Second Forum on Innovative Treatment Technologies,
Domestic and international, Philadelphia, PA, May 15-17,1990, EPA/540/2-90/006 (Abstracts) or EPA/
540/2-90/010 (Technical Papers).
U.S. Environmental Protection Agency, 1991. Engineering Bulletin: Thermal Desorptlon Treatment,
EPA/540/2-91/008.
NOTICE: This fact sheet is intended solely as general guidance and information. It is not intended, nor can it be relied upon, to create any rights enforceable by any
party in litigation with the United States. The Agency also reserves the right to change this guidance at any time without public notice.
•U.S. Government Printing Office: 1992—648-080/60006
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