Tire pyrolysis systems

• Metso recognized scrap tires as both an environmental problem and a waste of natural resources as oil, gas, carbon, and steel contained in the tire.
• Historical approach of burning tires in cement kilns, boilers, land filling and crumb rubber applications are an inefficient use and waste of natural resources.
• The main approach in the past was to get paid for the disposal of tires with secondary interest in the oil. Gas was sometimes burned in the tire process. The tire revenue could not sustain the plant cost in most cases.
• Uses of carbon product in secondary markets, asphalt extender, fuel and others did not significantly help the economics.  The ability to generate a carbon black product suitable for rubber use significantly improves the project economics.
• Metso developed our tire pyrolysis system to produce a high quality carbon product that could be used in rubber manufacturing and did not simply design our process as a tire disposal system. This requires that our process and plant design follow the same principles as the design of any chemical processing plant to provide consistent and safe operating conditions. The tire shreds feeding the system are treated as a process plant feedstock with a consistent feed rate to the system. The process is controlled with precision to insure that the temperature zones of the kiln stay within the set operating ranges. The carbon is cooled, has metals removed, is ground, and pelletized in consistent, controlled process stages.
• The plant has many stages but can be broken down into steps. A flow chart of steps that the tires must go through is shown to the side.
• Metso's pilot plant facilities were setup to evaluate the whole system on a continuous basis.  Over sixty (60) continuous pilot tests have been performed for a total of over 800 hours of continuous operation and over 32 tons of tires processed.
• Six (6) different feed materials have been tested at the pilot plant facility: passenger tires with steel, passenger tires without steel, off-road tires, manufacturer rejects, mixture of off-road and passenger tires and mixture of passenger and truck tires.
• Metso has been granted U.S. Patent No. 6,221,329 for “Pyrolysis Process of Reclaiming Desirable Materials from Vehicle Tires” as a result of our research and development of our tire pyrolysis process.
• Metso researched commercially available oil condensing systems and found them to be inadequate for consistently recovering oil from the difficult to handle pyrolysis process gas stream. As a result Metso developed our own condensing system and has been granted U.S. Patent No. 7,101,963 for “Condensing and Recovery of Oil from Pyrolysis Gas”.

Shredded and washed tire chips, approximately two inches by two inches, are received at the recycling facility.  The chips are fed to an indirect rotary kiln using special conveyors and air seals.

The indirect kiln the pyrolysis reaction is carried out and the chips go through three stages inside the kiln.  First, the rubber becomes brittle and separates from the steel (we call this rubber char).  In the second stage, the oil and gas are forced from the rubber char and swept from the kiln.  In the last tire pyrolysis stage, the char is fully processed into a carbon black-like substance and separated from the steel wires.

The char is sent through a Holo-Flite processor® (to cool it) and then sent to a grinding, pelletizing and bagging system where it is packaged for transport.

The steel is cooled and the steel wires are compacted and made available for transport to a steel recycler or steel processing furnace. 

The off-gas from the kiln is pulled through the Metso patented two stage condenser system where oil is extracted.  This recovered oil is very similar to diesel fuel in viscosity, heating value and other quality parameters, except that it has a significantly higher sulfur content and a lower flashpoint.  This pyrolysis oil could be used by any industry that currently burns oils with higher sulfur contents, such as number 4 through 6 fuel oils, or it can be further refined to remove the sulfur compounds.

In addition, there is a pyrolysis exhaust gas stream of non-condensable oil that can be used as a process fuel gas for industrial equipment or can be burned in a boiler and used for generating steam (for heating or power generation).