What Is Tire Recycling
Tire recycling is the process of converting end-of-life or unwanted old tires into material that can be utilized in new products. End-of-life tires typically become candidates for recycling when they become no longer functional due to wear or damage, and can no longer be re-treaded or re-grooved.
According to the tire industry, tire recycling is a major success story. The stockpile of scrap tires has shrunk from over a billion in 1991 to just 60 million by 2017.
There are over one billion end-of-life tires generated annually, worldwide. Around 249.4 million scrap tires were generated in the U.S. in 2017. Going back 100 years or so into the history of tires, tire recycling was a priority, with the price of an ounce of rubber rivaling the price of an ounce of silver. Such economic incentives faded, however. The introduction of synthetic rubber made from cheap imported oil, as well as by the adoption of steel belted radial tires made tires cheaper (less urgent to recycle) as well as more difficult to recycle. As a result, worn out tires increasingly found their way to landfills or were often dumped illegally. Fortunately, tires are now increasing diverted from landfills.
The Urgency of Diversion
About 16% of scrap tire generation was still landfilled in 2017. Old tires provide shelter for rodents and can trap water, providing a breeding ground for mosquitoes. In landfills, tires consume up to 75 percent airspace, In addition, tires may become buoyant and rise to the surface if they trap methane gases. This action can rupture landfill liners that are designed to prevent contaminants from polluting surface and groundwater. Recycling has been assisted through such programs as the Tire Stewardship BC Association and the work of leading recyclers such as Liberty Tire Recycling.
Markets for Scrap Tires
The three largest markets for scrap tires include tire-derived fuel (TDF), ground rubber applications/rubberized asphalt and civil engineering applications
Tire Derived Fuel
About 43% of scrap tires were consumed as TDF in 2018. TDF offers a viable alternative to the use of fossil fuels, as long as proper regulatory controls are in place. Major applications include Portland kilns (46% of TDF), pulp and paper (29%) and electric utility boilers (25%).
Depending on the type of combustion system, tires can be burned whole or in shredded form. Oftentimes tires must be reduced in size to fit combustion units, in addition to other preliminary processing. EPA notes the following benefits to burning tires for fuel:
- Tires produce the same amount of energy as oil and 25% more energy than coal;
- The ash residues from TDF may contain less heavy metals content than some coals;
- Results in lower NOx emissions when compared to many US coals, particularly the high-sulfur coals.
EPA stresses that facilities utilizing TDF should have a plan for tire storage and handling, necessary permits for applicable state and federal environmental programs; and be in compliance with all the requirements of that permit.
Ground Rubber Applications
Ground rubber applications accounted for 25% of scrap tire usage in 2017. Ground rubber is used to manufacture a number of products, ranging from asphalt rubber, through to track material, synthetic sports field underlay, animal bedding, and more.
The largest use of ground rubber is for asphalt rubber, utilizing approximately 220 million pounds or 12 million tires annually. The largest users of asphalt rubber are the states of California and Arizona, followed by Florida, with usage anticipated to grow in other states as well.
Civil Engineering Applications
Civil engineering applications consumed another 8% of U.S. scrap tire generation in 2017. Such applications can replace other materials such as polystyrene insulation blocks, drainage aggregate, or other types of fill. The EPA notes that significant material for civil engineering applications come from stockpiled tires, which are usually dirtier than other sources of scrap tires and can be used as embankment fill and in landfill projects.
While tire recycling has made huge gains, the industry notes that TDF demand has declined modestly in recent years, prompting it to continue to develop other markets such as ground rubber.