William D. Siuru Jr.

Americans discard about 240 million tires annually, about one per person, most of which end up in landfills. We also dispose of 1.3 million gallons of used oil, about 5 gallons per person, with 30 percent being dumped into landfills, on the ground or down sewers. Besides harming the environment, this represents a tremendous waste of resources. For instance, a typical tire contains as many British thermal units (Btu) of energy as two and one-half gallons of gasoline. In an effort to use these re-sources, scrap tires and used oil are being converted to energy sources through the tire liquefaction process (see chart).

In Texaco's tire liquefaction process, shredded tire chunks are placed in a liquefaction reactor to dissolve in hot oil. Since the temperature is relatively low, less than 700DegreesF, this method acts as a mild cracking process rather than pyrolysis, another tire recycling method. Two liquid products are produced: a light, condensate oil and a heavy, fuel oil-like tire oil. The light condensate oils can be refined into gasoline diesel, heating fuel or other chemicals.

The small amount of Btu gas produced in the process is used in the reactor's process heaters. Steel and fiberglass belting is filtered from the tire oil via a screen. After removing any oil coating in a high temperature cooking unit, the steel is sent to a metals reclaimer. The carbon black can be mixed with the tire oil and used as a fuel or a material in asphalt production.

Depending on the market, the tire oil can be used for several products. It can be distilled to produce marine or heating fuel and base lube oil stocks the same way that waste oils are now being recycled. The remaining components can be used for asphalt or if other options are not economical, the bulk of the tire oil can be turned directly into asphalt. The tire oil can also be refined like crude oil. But, there is a question about metals in tire oil which could potentially damage refinery equipment.

Another option is to feed a tire oil slurry to the Texaco gasification process. The company developed gasification technology in the 1950s to produce chemicals and fertilizers. Since then applications have expanded and Texaco has 40 gasifiers in use in addition to the 100 licenses that have been sold.

The gasifier is a cylindrical vessel that is lined with refractory materials to insulate the steel shell from the 2,500DegreesF gasification temperatures. A variety of raw materials including coal, industrial wastes, refinery tank sludge, plastics, contaminated soil, hazardous wastes, Orimulsion (Orinoco tar deposits) and tar oils are fed in slurry form to the gasifier. The gasifier is also supplied with oxygen. The gasifier produces synthesis gas (syngas) which is primarily hydrogen and carbon monoxide with small amounts of carbon dioxide and methane. Syngas, a very clean gas, is similar to natural gas in environmental qualities from which all particulate matter has been extracted. During gasification, sulfur is recovered as a by-product and all organics are destroyed in the high gasification temperatures. Metals are trapped in the slag extracted from the syngas after gasification.

Syngas can be used as a substitute for natural gas in a combined-cycle, electrical power generation system. The system includes both a gas turbine, similar to a jet engine, and a steam turbine that are connected to separate electric generators. Syngas is first combusted in the gas turbine, then the hot exhaust gases boil water to produce steam to drive the turbine.

For approximately $2 million, Texaco tire liquefaction systems can be built in 2,000 tire-per-day modular units using less than an acre of space. While the minimum commercially viable size is a 2,000 tires-per-day unit, expansion could come in 2,000 tire increments up to a maximum of 10,000 tires with a 50 to 60 percent incremental investment cost. A 2,000 tire unit would employ 10 people, and one tank truck could remove each day's production of tire oil.

Texaco says it is unlikely that the output from only a tire liquefaction unit could economically justify a gasification unit. For economical feasibility, the gasifier would have to be fed other materials like wastes, oil and coal.