Tire-Derived Fuel Frequent Questions
- Why use tires as fuel when there are other ways to recycle scrap tires?
- What are the trends of scrap tires used as fuel versus other market applications?
- What are the benefits of using tires as fuel?
- How do stack emissions vary from facilities that use TDF versus conventional fuels?
- What is the extent of dioxin/furan emissions from cement kilns or other facilities that use TDF?
- What are the emission and performance standards for facilities that use TDF?
- How is TDF regulated prior to processing?
- Have any standards been developed for the physical characteristics of TDF?
Why use tires as fuel when there are other ways to recycle scrap tires?
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 EPAs 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.
What are the trends of scrap tires used as fuel versus other market applications?
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.
Source: Rubber Manufacturers Association (RMA)
What are the benefits of using tires as fuel?
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.
How do stack emissions vary from facilities that use tire-derived fuel (TDF) versus conventional fuels?
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 dont 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 US.
Source: Air Emissions from Scrap Tire Combustion (PDF) (17 pp, 650K, about PDF), 1997
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.
What is the extent of dioxin/furan emissions from cement kilns or other facilities that use tire-derived fuel (TDF)?
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
What are the emission and performance standards for facilities that use tire-derived fuel (TDF)?
The national emission standards for hazardous air pollutants (NESHAP) for the portland cement manufacturing industry (40 CFR 63 subpart LLL) apply to all Portland cement kilns (including those that burn TDF) except for those that burn hazardous waste. The NESHAP includes emission limits and monitoring requirements for the following pollutants emitted from Portland cement kilns: particulate matter (as a surrogate for hazardous air pollutants (HAP) metals), dioxins/furans, and total hydrocarbons (as a surrogate for organic HAPs, including polycyclic organic matter). Facilities must perform testing for these pollutants and must repeat the tests if any significant change is made to the raw material components or fuels fed to the kiln that could lead to an increase in emissions of dioxins/furans or particulate matter (e.g., when there is an increase in the input rate of TDF). This rule was promulgated in 1999, amended in 2002, and additional amendments were proposed in December 2005.
Boilers that burn TDF at major source pulp and paper manufacturing facilities are subject to the NESHAP for Industrial, Commercial, and Institutional Boilers and Process Heaters (40 CFR 63 subpart DDDDD). See the Federal Register notice (September 13, 2004) for the final rule at 69 FR55217. The NESHAP includes emission limits and monitoring requirements for particulate matter (as a surrogate for HAP metals) or total selected metals (fuel analysis for arsenic, beryllium, cadmium, chromium, lead, manganese, nickel, and selenium), hydrogen chloride, and mercury. Facilities must perform testing for these pollutants and must repeat the tests if they plan to exceed the maximum fuel feed rate (set during the initial compliance test) of any of the solid fuels that are burned (e.g., when there is an increase in the input rate of TDF). This rule was promulgated in 2004 and amended in 2005.
How is TDF regulated prior to processing?
Day-to-day management of the collection of scrap tires is regulated at the state level. In 1985, Minnesota enacted the first state law for the management of scrap tires. Currently, 48 states have enacted laws or regulations that address scrap tire management.
Have any standards been developed for the physical properties of tire-derived fuel (TDF)?
Yes, in 2001, the American Society for Testing and Materials (ASTM) developed the following standard for shredded (not whole) tire derived fuel: Active Standard: D6700-01 Standard Practice for Use of Scrap Tire-Derived Fuel.
The following statement lists the scope of the TDF standard which is quoted from the ASTM website:
1.1 This practice covers and provides guidance for the material recovery of scrap tires for their fuel value. The conversion of a whole scrap tire into a chipped formed for use as a fuel produces a product called tire-derived fuel (TDF). This recovery practice has moved from a pioneering concept in the early 1980s to a proven and continuous use in the United States with industrial and utility applications.
1.2 Combustion units engineered to use solid fuels, such as coal or wood or both, are fairly numerous throughout the U.S. Many of these units are now using TDF even though they were not specifically designed to burn TDF. It is clear that TDF has combustion characteristics similar to other carbon-based solid fuels. Similarities led to pragmatic testing in existing combustion units. Successful testing led to subsequent acceptance of TDF as a supplemental fuel when blended with conventional fuels in existing combustion devices. Changes required to modify appropriate existing combustion units to accommodate TDF range from none to relatively minor. The issues of proper applications and specifications are critical to successful utilization of this alternative energy resource.
1.3 This practice explains TDFs use when blended and combusted under normal operating conditions with originally specified fuels. Whole tire combustion for energy recovery is not discussed herein since whole tire usage does not require tire processing to a defined fuel specification.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
To access ASTM standards, visit the ASTM website.
The answers to these questions were reviewed for technical accuracy by the TDF Committee of the RCC Scrap Tire Workgroup.