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
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. The use of TDF for heat production is controversial due to the possibility for toxin production. Reportedly, polychlorinated dibenzodioxins and furans 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.
Read more about this topic: Tire Derived Fuel