Figure 4-24: Typical Pyrolysis Process
Pyrolysis is formally defined as chemical decomposition induced in organic
materials by heat in the absence of oxygen. In practice, it is not possible to achieve a
completely oxygen-free atmosphere; actual pyrolytic systems are operated with less than
stoichiometric quantities of oxygen. Because some oxygen will be present in any pyrolytic
system, nominal oxidation will occur. If volatile or semivolatile materials are present in
the waste, thermal desorption will also occur.
Pyrolysis transforms hazardous organic
materials into gaseous components, small quantities of liquid, and a solid residue (coke)
containing fixed carbon and ash. Pyrolysis of organic materials produces combustible
gases, including carbon monoxide, hydrogen and methane, and other hydrocarbons. If the
off-gases are cooled, liquids condense producing an oil/tar residue and contaminated
water. Pyrolysis typically occurs under pressure and at operating temperatures above 430
°C (800 °F). The pyrolysis gases require further treatment. The off-gases may be treated
in a secondary combustion chamber, flared, and partially condensed. Particulate removal
equipment such as fabric filters or wet scrubbers are also required.
Conventional thermal treatment methods, such as rotary kiln, rotary hearth furnace, or
fluidized bed furnace, are used for waste pyrolysis. Kilns or furnaces used for pyrolysis
would be physically similar to the equipment described in Section
"Incineration", but would operate at lower temperature and
with less air supply than would be required for combustion. Molten salt process may also
be used for waste pyrolysis. These processes are described in the following sections:
The rotary kiln is a refractory-lined, slightly-inclined, rotating cylinder that serves
as a heating chamber.
Fluidized Bed Furnace
The circulating fluidized bed uses high-velocity air to circulate and suspend the waste
particles in a heating loop and operates at temperatures up to 430 °C (800 °F).
Molten Salt Destruction
Molten-salt destruction is another type of pyrolysis. In molten-salt destruction, a
molten salt incinerator uses a molten, turbulent bed of salt, such as sodium carbonate, as
a heat transfer and reaction/scrubbing meduim to destroy hazardous materials. Shredded
solid waste is injected with air under the surface of the molten salt. Hot gases composed
primarily of carbon dioxide, stream, and unreacted air components rise through the molten
salt bath, pass throught a secondary reaction zone, and through an off gas cleanup system
before discharging to the atmosphere. Other pyrolysis by-products react with the alkaline
molten salt to form inorganic products that are retained in the melt. Spent molten salt
containing ash is tapped from the reactor, cooled and placed in a landfill.
Pyrolysis is an emerging technology. Although the basic concepts of the process have
been validated, the performance data for an emerging technology have not been evaluated
according to methods approved by EPA and adhering to EPA quality assurance/quality control
standards. Performance data are currently available only for vendors. Also, existing data
are limited in scope and quantity/quality and are frequently of a proprietary nature.
Molten solid processing; Plasma pyrolysis.
The target contaminant groups for pyrolysis are SVOCs and pesticides. 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 wastes, and paint
Pyrolysis systems may be applicable to a number or organic materials that
"crack" or undergo a chemical decomposition in the presence of heat. Pyrolysis
has shown promise in treating organic contaminants in soils and oily sludges. Chemical
contaminants for which treatment data exist include PCBs, dioxins, PAHs, and many other
organics. Pyrolysis is not effective in either destroying or physically separating
inorganics from the contaminated medium. Volatile metals may be removed as a result of the
higher temperatures associated with the process but are similarly not destroyed.
Factors that may limit the applicability and effectiveness of the process
- There are specific feed size and materials handling requirements that impact
applicability or cost at specific sites.
- The technology requires drying of the soil to achieve a low soil moisture content (<
- Highly abrasive feed can potentially damage the processor unit.
- High moisture content increases treatment costs.
- Treated media containing heavy metals may require stabilization.
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 includes
soil moisture content and classification (no sieve analysis is necessary), and the soil
Limited performance data are available for pyrolytic systems treating
hazardous wastes containing PCBs, dioxins, and other organics. The quality of this
information has not been determined. These data are included as a general indication of
the performance of pyrolysis equipment and may not be directly transferrable to a specific
Superfund site. Site characterization and treatability studies are essential in further
refining and screening the pyrolysis technology.
The overall cost for remediating approximately 18,200 metric tons (20,000
tons) of contaminated media is expected to be approximately $330 per metric ton ($300 per
Technologies: Field Scale Demonstration Project in North America,
of Remediation Case Studies, Volume 4, June, 2000, EPA
California Base Closure Environmental Committee (CBCEC), 1994. Treatment
Technologies Applications Matrix for Base Closure Activities, Revision 1,
Technology Matching Process Action Team, November, 1994.
Guide to Documenting and Managing Cost and Performance Information for
Remediation Projects - Revised Version, October, 1998, EPA 542-B-98-007
Energy and Environment Research
Center, 1994. Thermal Recycling of Plastics. Energy and
Environment Research Center, University of North Dakota, Grand Forks, ND.
EPA, 1992. AOSTRA-SoilTech Anaerobic Thermal Processor: Wide Beach
Development Site, Demonstration Bulletin, EPA, ORD, Washington, DC,
EPA, 1992. Pyrolysis Treatment, Engineering Bulletin, EPA,
OERR, Washington, DC, EPA/540/S-92/010.
EPA, 1992. SoilTech Anaerobic Thermal Processor: Outboard Marine
Corporation Site, Demonstration Bulletin, EPA, ORD, Washington, DC,
Shah, J.K., T.J. Schultz, and V.R. Daiga, 1989. "Pyrolysis Processes."
Section 8.7 in Standard Handbook of Hazardous Waste Treatment and Disposal,
ed. H.M. Freeman. McGraw-Hill Book Company, New York, NY.
Points of Contact:
General FRTR Agency Contacts
Technology Specific Web Sites:
Government Web Sites
Non Government Web Sites
A list of vendors offering
En 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
Health and Safety:
To be added