Americans dispose of about 300 million worn-out tires each year, and since tires are not biodegradable, they end up consuming a lot of space. Many states have prohibited the discarding of whole tires into landfills because, in addition to taking up extra room, buried tires in landfills collect air and methane and rise to the surface over time. Burning scrap tires release carcinogens and other poisons into the air, and the fires are difficult to extinguish and can often last for days or even weeks. Fortunately, scrap tires are recyclable, and through a process known as pyrolysis, they can be broken down into their original components, which can then be reused.
The Pyrolysis Process
In the pyrolysis process, the whole or shredded tire is heated in a reactor vessel that contains an oxygen-free atmosphere. The rubber melts in the reactor, and the rubber polymers break down into smaller molecules, which eventually vaporize and exit the reactor. These vapors may then be burned to produce power or condensed into an oil-like liquid which can then be used as a fuel. The larger molecules that cannot be condensed remain as a gas, which is used to provide heat for the process.
The minerals and carbon that were part of the tire—about 40 percent by weight—are removed as a solid. The steel from the tire can be removed from the solid stream with magnets and can be recycled for reuse in industrial manufacturing. The remaining material is a carbonaceous char, which can be refined into carbon black. Carbon black is a substance that is used in the production of new tires and other rubber-related goods, as well as a fuel source for power generation or in cement kilns.
Measuring the Benefits
When performed well, tire pyrolysis is a clean process with little to no emissions or waste. A 20-pound tire yields about five to nine pounds of carbon, 1.5 to 2.5 gallons of fuel oil, more than 50,000 Btu’s of gas and around two to three pounds of scrap steel. The process begins with weighing the tires. The tires are then introduced into the pyrolysis plant whole or shredded, halved or chopped. Whether the tires are left whole or shredded depends on the type of plant used. Similarly, the length of time the process takes varies from unit to unit. Some units are batch, which means they process one group of tires completely before starting the next. Other units are continuous, providing a constant stream of product.
The resulting products can be recycled for reuse. The primary product of tire pyrolysis is tire oil, which many industries use as fuel. Carbon black, another product of pyrolysis, has multiple uses, including as a chemical strengthener in rubber and a coloring agent. There is a huge demand for carbon black in the rubber industry. The steel wire recycled from tires in pyrolysis can be sold as scrap.
The pyrolysis operation diverts waste tires from landfills and prevents them from potentially harming the environment. Unlike hazardous fires caused by waste tires, the pyrolysis process does not cause significant air pollution. The operation also produces materials that may be reused or sold, making tire pyrolysis a viable economic opportunity.
For more information, contact Worldwide Recycling Equipment Sales, at (660) 263-7575 or [email protected].