Tire derived fuel
Encyclopedia
Tire-derived fuel is composed of shredded tires. Tires may be mixed with coal or other fuels such as wood to be burned in concrete kilns, power plants, or paper mills. The use of TDF for heat production is controversial due to the possibility for toxin production.
Tire Derived Fuel is a temporary solution to the scrap tire waste problem. Recent advances in tire recycling technology might one day provide a solution other than burning by reusing tire derived material in high volume applications.
s 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.
On one hand, some argue that it is better to use the energy stored in a tire than to put it in a landfill, in line with the waste hierarchy. On the other, it is difficult to justify introducing toxins into the atmosphere, and much energy can be saved by recycling the tires so that new ones do not need to be remanufactured from raw materials.
This fuel has a very high energy content, with an average heat value of 15,500 BTUs per pound of fuel. This is roughly the same as heavy petroleum fuel oils. Fuel begins to burn (flash point
) at 550 to 650 degrees Fahrenheit. Complete combustion is achieved with flame temperatures of 1,202 degrees Fahrenheit.
Environmental concerns about this fuel focus on the chemical contents of the tire other than hydrocarbons. Tires are constructed with steel belts which give shape and structure to the tread and sometimes to the sidewall. Much of this wire is removed when tires are shredded to make TDF, however certainly not all of it will be removed. Therefore it is no surprise that the ash contains a large mass percentage of iron. Zinc
, chromium
, cadmium
and lead
make up the bulk of the remaining heavy metals in the ash. The alkaline earth metal calcium is also present in significant quantity. Fluorine
, chlorine
, sulfur
, and nitrogen
make up the bulk of the non-metal content of the ash.
One tire manufacturing process involves a salt bath, which likely explains the high content of calcium. Trace heavy metals may be explained by metals added for alloying purposes to the steel wire in the belts.
Tires are typically composed of about 1 to 1.5% Zinc oxide
, 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 liner that slows the leak rate of air. The Rubber Manufactures Association (RMA) is a very good source for compositional data and other information on tires.
and furans in the flue gases. Zinc has also been found to leach 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, paper mills, 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 emsissions. 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 of Tire rubber use in energy generation, deeply studies the environmental impact on soil, water, and air from combustion of waste rubber (TDF).
Alvarez research shows that huge polyaromatic 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, and carcinogenic pollutants, as well as hot- gas cleaning systems and COx capture systems."
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 as petroleum and approximately 25% more energy than coal, Burning tires is lower on the hierarchy of reducing waste than recycling, but it is better than placing the tire waste in a landfill or dump. There is a possibility for tire fires or the harboring of disease vectors such as mosquitoes.Tire Derived Fuel is a temporary solution to the scrap tire waste problem. Recent advances in tire recycling technology might one day provide a solution other than burning by reusing tire derived material in high volume applications.
Controversy
Reportedly, polychlorinated dibenzodioxins and furanFuran
Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen. The class of compounds containing such rings are also referred to as furans....
s 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.
On one hand, some argue that it is better to use the energy stored in a tire than to put it in a landfill, in line with the waste hierarchy. On the other, it is difficult to justify introducing toxins into the atmosphere, and much energy can be saved by recycling the tires so that new ones do not need to be remanufactured from raw materials.
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 RemovedThis fuel has a very high energy content, with an average heat value of 15,500 BTUs per pound of fuel. This is roughly the same as heavy petroleum fuel oils. Fuel begins to burn (flash point
Flash point
The flash point of a volatile material is the lowest temperature at which it can vaporize to form an ignitable mixture in air. Measuring a flash point requires an ignition source...
) at 550 to 650 degrees Fahrenheit. Complete combustion is achieved with flame temperatures of 1,202 degrees Fahrenheit.
Environmental concerns about this fuel focus on the chemical contents of the tire other than hydrocarbons. Tires are constructed with steel belts which give shape and structure to the tread and sometimes to the sidewall. Much of this wire is removed when tires are shredded to make TDF, however certainly not all of it will be removed. Therefore it is no surprise that the ash contains a large mass percentage of iron. Zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
, cadmium
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...
and lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
make up the bulk of the remaining heavy metals in the ash. The alkaline earth metal calcium is also present in significant quantity. Fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...
, chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
, sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
, and nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
make up the bulk of the non-metal content of the ash.
One tire manufacturing process involves a salt bath, which likely explains the high content of calcium. Trace heavy metals may be explained by metals added for alloying purposes to the steel wire in the belts.
Tires are typically composed of about 1 to 1.5% Zinc oxide
Zinc oxide
Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...
, 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 liner that slows the leak rate of air. The Rubber Manufactures Association (RMA) is a very good source for compositional data and other information on tires.
Toxicity
While environmental controversy surrounding use of this fuel is wide and varied, the greatest supported evidence of toxicity comes from the presence of dioxinsDioxins and dioxin-like compounds
Dioxins and dioxin-like compounds are by-products of various industrial processes, and are commonly regarded as highly toxic compounds that are environmental pollutants and persistent organic pollutants . They include:...
and furans in the flue gases. Zinc has also been found to leach 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, paper mills, 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 emsissions. 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 of Tire rubber use in energy generation, deeply studies the environmental impact on soil, water, and air from combustion of waste rubber (TDF).
Alvarez research shows that huge polyaromatic 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, and carcinogenic pollutants, as well as hot- gas cleaning systems and COx capture systems."