Pyrolysis of tires involves the application of heat to produce chemical changes and derive various products such as oil and carbon black. The oil produced by the process would have to compete with oil conventionally produced from crude, at its current prices. There is also the problem of marketing the char by-products, whose prices are highly dependent on quality.
The history of tire pyrolysis projects to date indicates that the problems blocking them have been technical and economic. These include the problems of upgrading the carbon black by-product while keeping down the operating cost of the process and the capital cost of the plant.
Firestone Tire & Rubber Company performed a major cooperative research program with the U.S. Bureau of Mines in the early 1970s. They developed a 10 tire per day laboratory pyrolysis unit. In their studies they determined average yields of pyrolysis products per tire as follows: 1 gallon oil, 7 pounds char, 3 pounds gas (57 scf), and 2 pounds steel and ash. Generally, most pyrolysis systems have produced similar yields.
Thus, it is important that any successful pyrolysis plant make provisions for selling the by-products, especially the char.
Recently, there has been a technical advance in char upgrading that may help to make tire pyrolysis economically feasible. In 1987, American Tire Reclamation (ATR) filed for a patent on a method of reclaiming carbon black from discarded tires. This method is intended to separate the char into a medium grade (Grade A) carbon black and a low grade (Grade B) char residue containing 15% ash. This classifier produces a carbon black with the particle size, consistency, and purity that are suitable for a semi-reinforcing filler of medium strength.
Conrad Industries operates a pyrolysis unit in Centralia, Washington. Other firms involved in tire pyrolysis include: Nu-Tech Systems; J.H. Beers, Inc.; Baltimore Thermal; and TecSon Corporation.
There are essentially no process emissions from pyrolysis units. The primary sources of emissions are fugitive sources (for particulate emissions) and equipment leaks (for VOC emissions). The fugitive particulate emissions come from handling, crushing, screening, and packaging the char by-product from the process. There is nothing meritorious about these emissions and they can be handled using standard dust control practices, canopy hoods for dust collection, and a baghouse for particulate removed. The dust generated does not appear to be hazardous.
The VOC emissions occur from leaks around valve stems, pump shafts, worn packings, and pipe joints. Fugitive VOC emissions can be minimized with proper design and specifying seal-less pumps and valves, and with good preventive maintenance.
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