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.