Fact sheet: Pyrolysis

From: Public Services and Procurement Canada

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Description

Pyrolysis, also called molten solid processing or plasma pyrolysis, is defined as chemical decomposition of organic materials induced by heat. In contrast to incineration, pyrolysis occurs in the almost complete absence of oxygen (less than stoichiometric quantities of oxygen). This treatment transforms organic materials into gas (syngas), small quantities of liquid, and a solid residue (coke) containing fixed carbon and ash. Pyrolysis treatment does not produce toxic gases from the combustion process, and the syngas is generally composed of carbon monoxide, hydrogen, methane and other hydrocarbons. The gas emissions require further treatment before being released into the atmosphere.

Pyrolysis reactions typically occur under pressure and at temperatures above 430 0C (800 0F). There are various conventional pyrolysis treatments including rotary kiln, rotary hearth furnace, fluidized bed furnace and pyrolysis with molten salt destruction.

Rotary Kiln (Rotary Hearth Furnaces)

The rotary kiln is a refractory-material lined, slightly inclined rotating cylinder that serves as a heating chamber. Kilns or furnaces used for pyrolysis are physically similar to the equipment used during the incineration process, but operate at lower temperatures and without oxygen.

Fluidized Bed Furnace

The fluidized bed furnace uses high-velocity air to circulate and suspend the waste particles in a heating loop and operates at temperatures up to 430 0C (800 0F). The turbulence produces a uniform temperature around the pyrolysis chamber and a hot cyclone. The fluidized bed technique completely mixes the contaminated material.

Pyrolysis with Molten Salt Destruction

Pyrolysis combined with molten salt destruction (MSD) is another type of pyrolysis treatment that is similar to the fluidized bed furnace. Once the contaminated material is treated by pyrolysis, the resulting hot gases rise through a molten salt bath and a gas emission cleanup system before being discharged into the atmosphere. Acidic by-products of pyrolysis react with the alkaline molten salt to form inorganic products that are retained in the molten salt. Because the salt bath is liquid, it also removes some particulates from the gas. After several pyrolytic cycles, the molten salt within the reactor is replaced.

The target contaminants for pyrolysis are semi-volatile organic compounds (SVOCs) and pesticides. The process is applicable for the treatment of a variety of organics derived 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 waste.

Sources :

Other information recommended for detailed characterization

Phase III

  • Volume of contaminated material to treat

Recommended analyses for detailed characterization

Chemical analysis

  • Contaminant concentrations:
    • identification and concentration of all contaminants (sorbed, dissolved, and free phase)

Physical analysis

  • Soil water content
  • Matrix fusion temperature

Notes:

Treatability studies are recommended to identify potential gas emissions and the composition of the resulting coke are required.

Applications

  • The target contaminants for pyrolysis include SVOCs and pesticides
  • Pyrolytic systems may be used to treat a number or organic materials that decompose in the presence of heat
  • This technology is applicable to residual and free phase contamination

Treatment type

Treatment typeApplies or Does not apply
In situ
Does not apply
Ex situ
Applies
Biological
Does not exist
Chemical
Does not exist
Control
Does not exist
Dissolved contamination
Does not exist
Free Phase
Applies
Physical
Applies
Residual contamination
Applies
Resorption
Applies
Thermal
Applies

State of technology

State of technologyExist or Does not exist
Testing
Exist
Commercialization
Exist

Target contaminants

Target contaminantsApplies, Does not apply or With restrictions
Aliphatic chlorinated hydrocarbons
Applies
Chlorobenzenes
With restrictions
Explosives
Applies
Monocyclic aromatic hydrocarbons
With restrictions
Non metalic inorganic compounds
Does not apply
Pesticides
Applies
Petroleum hydrocarbons
Applies
Phenolic compounds
With restrictions
Policyclic aromatic hydrocarbons
Applies
Polychlorinated biphenyls
With restrictions

Treatment time

Treatment timeApplies or Does not apply
Less than 1 year
Applies
1 to 3 years
Does not apply
3 to 5 years
Does not apply
More than 5 years
Does not apply

Secondary by-products and/or metabolites

  • Pyrolytic by-products from the combustion of organic compounds are syngas, small quantities of liquid and coke
  • The syngas generally contains carbon monoxide, hydrogen, methane and other hydrocarbons
  • Decomposition of chlorinated organic compounds by pyrolysis has the potential to produce toxic compounds such as dioxins and furans due to incomplete combustion MSD treatment after pyrolysis eliminates the release of dioxins and furans
  • When the gas emissions are cooled, liquids condense, producing an oil/tar residue and contaminated water These oils/tar residues may be toxic and require proper treatment, storage and disposal

Limitations of the technology

  • Limited performance when treating soil contaminated with polychlorinated biphenyls (PCBs) and dioxins
  • Pyrolysis does not treat inorganic compounds
  • Volatile metals may be removed as a result of the high temperatures associated with the treatment but are not destroyed
  • Depending upon the amount and the type of contaminants treated, the used molten salt may be toxic, in which case special treatment or disposal may be required
  • Coke containing heavy metals may require stabilization before final disposal
  • Highly abrasive material can potentially damage the processor unit

Complementary technologies that improve treatment effectiveness

  • Pyrolytic treatment requires drying of the soil before treatment

Required secondary treatments

  • Gas emission quality monitoring and treatment when necessary
  • Proper treatment and disposal of the waste products (liquid, coke, ash, etc.)

Application examples

Application examples are available at this address:

Performance

Pyrolysis is an emerging technology. Performance data is limited in scope and in quantity/quality. Treatability studies are essential to further refine pyrolysis technology.

References

Author and update

Composed by:Josée Thibodeau, M.Sc National Research Council

Latest update provided by:Martin Désilets, B.Sc. National Research Council

Updated Date: March-07-19

Version:
1.0