Worldwide, it is estimated that one billion scrap tires are produced every year. Instead of burning the tires, the Metso Outotec system roasts them at a lower temperature in an atmosphere devoid of oxygen (so that no actual burning will occur). This method of roasting is called pyrolysis, and is used for many different processes. By using pyrolysis, the tire shreds are broken down into their three basic components: carbon black char, steel radials and oil/gas.
From a single tire, approximately 1/3 of the weight is steel, 1/3 becomes pyro black (carbon black plus additives) and the final 1/3 is oil/gas. The products from the tire pyrolysis system are carbon black char, oil (similar to number 2 grade fuel oil), steel and non-condensable gases.
The tire pyrolysis system consists of an indirectly fired rotary kiln, steel recovery, char handling, grinding & pelletizing circuit, oil condensing system and gas cleaning system. The system is designed to operate 24 hours per day, 7 days per week.
This product line system offers a true recycling solution to the large amount of rubber used in tires and industrial products. Recycled materials can be used to make new rubber products.
Metso Outotec 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 Outotec 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 Outotec 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).