In its simplest definition, tire-derived fuel (TDF) is nothing other than tires that have outlived their usefulness and are destined for terminal use as fuel. More commonly, TDF is taken to mean scrapped tires that have been through a powerful shredder. These shreds are usually mixed with other fuels like coal or wood for combustion in power plants, paper mills, concrete kilns, etc.
Discarded tires, actually shredded scraps of tire rubber, find good final use as fuel as they have rather high heat-generating value; in fact, studies have shown that it is preferable to extract residual energy by burning tire shreds in place of using it as landfills. Going back to 2003, about 130 million discarded tires were burned as fuel (nearly 45 percent of all fuel generated), up close to fivefold from the 25.9 odd million (nearly 10.7 percent of all fuel) burned in 1991.
Semanticists will say that TDF must include complete tires also, since they are used-even if seldom- in large furnaces. This claim, while true in the general sense, can be diffused by arguing that tires have to be generally reduced in terms of size to small shreds to be burned in the average combustion unit. Moreover, most tires need extra physical processing like dewiring and removal of metallic contents, if any. Complete tires are rarely used as fuel.
Scraps of tires are typically utilized to supplement traditional fuels like wood or fossil fuel like coal. Burning TDF has numerous advantages:
TDF gives off an equal quantity of energy when compared with oil plus 25 percent excess energy when compared with coal;
TDF residual ash generally contains a lesser heavy metal component compared to some coal families;
Results in less NOX, [mono-nitrogen oxides NO and NO2 (nitric oxide and nitrogen dioxide)] emission in comparison to a lot of coals, especially high-sulfur content coals.
Over 290 million tires were discarded in the U.S. in 2003. Nearly a third of these (100 million) were recycled to make new products, whereas 130 million discarded tires found application as TDF in a range of industrial services. TDF is proving to be one of numerous viable alternatives that can preclude freshly created scrapped tires from unsuitable removal as tire piles, as also for bringing down or eradicating extant tire stockpiles.