Tire-derived fuel (TDF) is composed of shredded scrap tires. Tires may be mixed with

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...

or other fuels, such as wood or chemical wastes, to be burned in concrete kilns,

power plant A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the electricity generation, generation of electric power. Power stations are generally connected to an electr ...

s, or

paper mill A paper mill is a factory devoted to making paper from vegetable fibres such as wood pulp, old rags, and other ingredients. Prior to the invention and adoption of the Fourdrinier machine and other types of paper machine that use an endless belt ...

s. An EPA test program concluded that, with the exception of

zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...

emissions Emission may refer to: Chemical products * Emission of air pollutants, notably: ** Flue gas, gas exiting to the atmosphere via a flue ** Exhaust gas, flue gas generated by fuel combustion ** Emission of greenhouse gases, which absorb and emit rad ...

, potential emissions from TDF are not expected to be very much different from other conventional fossil fuels, as long as

combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion ...

occurs in a well-designed, well-operated and well-maintained combustion device. In the United States in 2017, about 43% of scrap tires (1,736,340 tons or 106 million tires) were burnt as tire-derived fuel. Cement manufacturing was the largest user of TDF, at 46%, pulp and paper manufacturing used 29% and electric utilities used 25%. Another 25% of scrap tires were used to make ground rubber, 17% were disposed of in landfills and 16% had other uses.

Theory

Historically, there has not been any volume use for scrap tires other than burning that has been able to keep up with the volume of waste generated yearly. Tires produce the same

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

petroleum Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...

and approximately 25% more energy than coal.

Burning tires Tire fires are events that involve the combustion of large quantities of tires, usually waste tires, typically in locations where they are stored, dumped, or processed. They exist in two forms: as fast-burning events, leading to almost immediat ...

is lower on the hierarchy of reducing waste than

recycling Recycling is the process of converting waste materials into new materials and objects. This concept often includes the recovery of energy from waste materials. The recyclability of a material depends on its ability to reacquire the propert ...

, but it is better than placing the tire waste in a

landfill A landfill is a site for the disposal of waste materials. It is the oldest and most common form of waste disposal, although the systematic burial of waste with daily, intermediate and final covers only began in the 1940s. In the past, waste was ...

or dump, where there is a possibility for uncontrolled tire fires or the harboring of disease vectors such as mosquitoes. Tire Derived Fuel is an interim solution to the scrap tire waste problem. Advances in

tire recycling Tire recycling, or rubber recycling, is the process of recycling waste tires that are no longer suitable for use on vehicles due to wear or irreparable damage. These tires are a challenging source of waste, due to the large volume produced, th ...

technology might one day provide a solution other than burning by reusing tire derived material in high volume applications.

Characteristics

Tire derived fuel is usually consumed in the form of shredded or chipped material with most of the metal wire from the tire's steel belts removed. The analytical properties of this refined material are published in TDF Produced From Scrap Tires with 96+% Wire Removed. Tires are typically composed of about 1 to 1.5%

Zinc oxide Zinc oxide is an inorganic compound with the Chemical formula, formula . It is a white powder which is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, Zinc metabolism, food supplements, rubbe ...

, which is a well known component used in the manufacture of tires and is also toxic to aquatic and plant life. The chlorine content in tires is due primarily to the chlorinated

butyl rubber Butyl rubber, sometimes just called butyl, is a synthetic rubber, a copolymer of isobutylene with isoprene. The abbreviation IIR stands for isobutylene isoprene rubber. Polyisobutylene, also known as "PIB" or polyisobutene, (C4H8)n, is the homop ...

liner that slows the leak rate of air. The

Rubber Manufacturers Association The U.S. Rubber Manufacturers Association (RMA), established in 1915 as the Rubber Club of America, is a national trade and advocacy group of U.S. rubber tire manufacturers. The Rubber Manufacturers Association formed the Tire Industry Safety Cou ...

(RMA) is a very good source for compositional data and other information on tires. The use of TDF for heat production is controversial due to the possibility for toxin production. Reportedly,

polychlorinated dibenzodioxins Polychlorinated dibenzodioxins (PCDDs), or simply dioxins, are a group of long-lived polyhalogenated organic compounds that are primarily anthropogenic, and contribute toxic, persistent organic pollution in the environment. They are commonly ...

and

furans Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as furans. Furan is a colorless, flammable, highly ...

are produced during the combustion process and there is supportive evidence to suggest that this is true under some incineration conditions. Other toxins such as NOx, SOx and heavy metals are also produced, though whether these levels of toxins are higher or lower than conventional coal and oil fired incinerators is not clear.

Environmental impact

While environmental controversy surrounding use of this fuel is wide and varied, the greatest supported evidence of toxicity comes from the presence of

dioxins Dioxins and dioxin-like compounds (DLCs) are a group of chemical compounds that are persistent organic pollutants (POPs) in the environment. They are mostly by-products of burning or various industrial processes or, in the case of dioxin-like PC ...

and furans in the flue gases. Zinc has also been found to dissolve into storm water, from shredded rubber, at acutely toxic levels for aquatic life and plants. A study of dioxin and furan content of stack gasses at a variety of cement mills,

s, boilers, and power plants conducted in the 1990s shows a wide and inconsistent variation in dioxin and furan output when fueled partially by TDF as compared to the same facilities powered by only coal. Some facilities added as little as 4% TDF and experienced as much as a 4,140% increase in dioxin and furan emissions. Other facilities added as much as 30% TDF and experienced dioxin and furan emissions increases of only as much as 58%. Still other facilities used as much as 8% TDF and experienced a decrease of as much as 83% of dioxin and furan emissions. One facility conducted four tests with two tests resulting in decreased emissions and two resulting in increased emissions. Another facility also conducted four tests and had widely varying increases in emissions. A 2004 study showed that huge

polyaromatic A Polycyclic aromatic hydrocarbon (PAH) is any member of a class of organic compounds that is composed of multiple fused aromatic rings. Most are produced by the incomplete combustion of organic matter— by engine exhaust fumes, tobacco, incine ...

emissions are generated from combustion of tire rubber, at a minimum, 2 orders of magnitude higher than coal alone. The study concludes with, "atmospheric contamination dramatically increases when tire rubber is used as the fuel. Other different combustion variables compared to the ones used for coal combustion should be used to avoid atmospheric contamination by toxic,

mutagenic In genetics, a mutagen is a physical or chemical agent that permanently changes genetic material, usually DNA, in an organism and thus increases the frequency of mutations above the natural background level. As many mutations can cause cancer in ...

, and

carcinogenic A carcinogen () is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and Biological agent, biologic agent ...

pollutants, as well as hot-gas cleaning systems and COx capture systems."

References

{{rubber Fuels Chemical engineering Tires