Frequently Asked Questions
Question: Why use tires as fuel when there are other ways to recycle scrap tires?
Answer: Tire-derived fuel (TDF) was the first market for scrap tires. From 1979 until 1992 TDF was the primary market for tires. Beginning in 1992, whole scrap tires were used as feedstock for ground rubber and processed tires were used in civil engineering applications. Based on over 15 years of experience with more than 80 individual facilities, EPA recognizes that the use of tire-derived fuels is a viable alternative to the use of fossil fuels (see EPA’s TDF factsheet (PDF) (1 pg, 12K, About PDF). In order to prevent tires from being stockpiled or disposed of in landfills, diverse markets need to be in place to handle the approximately 290 million scrap tires that are generated annually.
Scrap tire-derived fuel, or TDF, is used because of its high heating value. Compared to other commonly used solid fuels, the heating value is 25-50% higher than coal and 100-200% higher than wood. Facilities such as utility boilers, cement kilns, and pulp/paper mills use TDF as supplemental fuel in their energy-intensive processes. State and Federal studies have repeatedly shown that using tires to generate energy is environmentally sound when used in appropriate applications that ensure complete combustion, have proper air pollution controls in place, and conduct all required testing, monitoring, and other regulatory requirements. Furthermore, scrap tires that are removed from stockpiles only have two uses in the current markets: TDF and limited civil engineering applications. This is because, over time, tires in piles become contaminated with water, dirt and other debris. This “contamination” is generally what prohibits these tires from being used as feedstock for ground rubber.
Question: What are the trends of scrap tires used as fuel versus other market applications?
Answer: In 1990, 25 million tires (which is about 11 percent of the total number of scrap tires generated) were used in TDF. This represented 98 percent of the market for scrap tires. Since 1992 the number of tires used as TDF has increased, but the percentage of the overall number of tires going to this market has decreased.
In 2003, 127 million tires were used as TDF, but represented only 44 percent of scrap tires going to market applications since other markets have developed.
Question: What are the benefits of using tires as fuel?
Answer: There are several benefits to using tires as fuel:
- Use of tire derived fuel (TDF) reduces the amount of fossil fuels that would otherwise be consumed.
- TDF is less expensive than fossil fuels.
- Diversion of tires from landfills reserves landfill capacity for other municipal waste and helps prevent scrap tire piles. Scrap tire piles pose risks because they provide habitat for disease vectors (such as mosquitoes and rodents), and because they can catch fire, creating large amounts of toxic smoke and hazardous liquids that can contaminate air, water and soils.
- Some state agencies suggest that cement kilns add TDF to their coal fuel in order to decrease emissions of oxides of nitrogen (NOx).
- TDF offers the potential advantage of decreasing emissions of oxides of sulfur (SOx) when used to replace high sulfur coal in cement kiln applications.
- In cement kiln applications, the ash resulting from TDF and coal combustion becomes an integral component of the product, eliminating the landfilling of ash.
Question: How do stack emissions vary from facilities that use tire-derived fuel (TDF) versus conventional fuels?
Answer: EPA and state testing has shown that TDF produces emissions comparable to other conventional fuels. At well controlled facilities, emissions will not change significantly when TDF is used to replace some of the typical fuel used at the facility. It is important to note that there are variations from test to test at plants that don’t use TDF, even when every attempt is made to hold operating conditions constant. Facilities have to meet regulatory limits when they use this fuel or other fuels and must demonstrate through compliance testing that they are achieving the applicable emission limitations.
The following statement is from an EPA research paper on use of TDF:
“TDF can be used successfully as a 10-20% supplementary fuel in properly designed fuel combustors with good combustion control and add-on particulate controls, such as electrostatic precipitators, or fabric filters. Furthermore, a dedicated tire-to-energy facility specifically designed to burn TDF as its only fuel has been demonstrated to achieve emission rates much lower than most solid fuel combustors. No field data were available for well-designed combustors with no add-on particulate controls. Laboratory testing of a Rotary Kiln Incinerator Simulator (RKIS) indicated that efficient combustion of supplementary TDF can destroy many volatile and semi volatile air contaminants. However, it is not likely that a solid fuel combustor without add-on particulate controls could satisfy air emission regulatory requirements in the U. S”.
EPA and states are in the process of gathering stack test data from US plants using TDF in order to include in a comprehensive database. Emission sampling results from one cement kiln showed that carcinogenic risk declined when TDF was burned as a fuel.
Question: What is the extent of dioxin/furan emissions from cement kilns or other facilities that use tire-derived fuel (TDF)?
Answer: Dioxin/furan emissions at cement kilns are primarily a function of exhaust gas temperature in the air pollution control device, which is typically either a fabric filter or electrostatic precipitator. EPA has previously determined that the type of fuel used (e.g., coal vs. alternative fuels) likely does not affect dioxin/furan emission rates. Regardless of the fuel used, cement kilns must comply with stringent limits on dioxin/furan emissions (0.2 ng TEQ/dscm or 0.4 ng TEQ/dscm and limited air pollution control device inlet temperature)1. Dioxin/furan emissions at cement plants can vary widely within the allowable range, regardless of whether TDF is used. Limited data suggests that use of TDF in cement kilns does not adversely impact dioxin and furan emissions. Note that when comparing measured dioxin/furan emission rates from the same source (both with and without TDF), the differences in measured emissions may be more attributable to measurement sensitivities and/or test-to-test variations in the factors that influence measured dioxin/furan emissions and not due to the use of TDF itself.
1 ng = nanograms; TEQ = toxicity equivalent quotient, the international method of relating the toxicity of various dioxin/furan congeners to the toxicity of 2,3,7,8-TCDD; dscm = dry standard cubic meters