Tire pyrolysis

OVERVIEW OF PROCESS UNITS BURNING TIRES FOR FUEL. 159 

The information in Part I is from Markets for Scrap Tires, prepared by the U.S. Environmental Protection Agency Office of Solid Waste, October 1991. 

The management of scrap tires has become a growing problem in recent years. Scrap tires represent one of several special wastes that are difficult for municipalities to handle. Whole tires are difficult to landfill because they tend to float to the surface. Stockpiles of scrap tires are located in many communities, resulting in public health, environmental, and aesthetic problems. 

This report discusses the problems associated with scrap tires and identifies existing and potential source reduction and utilization methods that may be effective in solving the tire problem. Barriers to increased utilization and options for removing the barriers are identified and evaluated. 

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Nippon Zeon estimated that the break-even cost of its tire pyrolysis pilot plant was 0.25 per tire (29,30). One study indicates that pyrolysis of tires and other polymers should be considered as a means for disposing of scrap within environmental constraints. A plant processing 81,000 t/yr of scrap could be profitable, based on sales of reclaimed products (31). 

Conrad Industries, Inc. (CentraUa, Washington) and Clean Air Products Company (Pordand, Oregon) have jointiy built a tire pyrolysis demonstration machine which allows recovery of combustible gases, oils, and other by-products. The equipment can also handle other carbonaceous material. It is designed to process 0.9 t/h of tires the entire system is estimated to cost about 2.3 x 10 . The feedstock consists of 5-cm tires chips which produce pyrolytic filler, a vapor gas yielding 11.5 kj/m (1000 Btu/ft ), and medium and light oils yielding about 42 MJ/kg (18,000 Btu/lb) (32). 

Kutrieb Corporation (Chetek, Wisconsin) operates a pyrolator process for converting tires into oil, pyrolytic filler, gas, and steel. Nu-Tech (Bensenvike, Illinois) employs the Pyro-Matic resource recovery system for tire pyrolysis, which consists of a shredding operation, storage hopper, char-coUection chambers, furnace box with a 61-cm reactor chamber, material-feed conveyor, control-feed inlet, and oil collection system. It is rated to produce 272.5 L oil and 363 kg carbon black from 907 kg of shredded tires. TecSon Corporation (Janesville, Wisconsin) has a Pyro-Mass recovery system that pyroly2es chopped tire particles into char, oil, and gas. The system can process up to 1000 kg/h and produce 1.25 MW/h (16). 

Data for the Wastewater Stream of Tire Pyrolysis Plant... 

Conessa, J.A., FuUena, A., and Font, R., Tire pyrolysis Evolution of volatile and semivolatile compounds, Energy Fuel, 14, 409, 2000. 

Scrap tire pyrolysis, 22 466-467 Scrap tire regulations, 22 462 Scrap tire utilization projects, goal of, 22 478... 

The history of tire pyrolysis projects to date indicates that the problems blocking them have been technical and economic (60). 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. 

In the past several years, tire pyrolysis has not looked profitable, primarily because of the technical problems of upgrading the char. The next few years should determine whether ATR s new char classification technology can help to overcome these problems. 

Up to as recently as a year ago there were no commercially operating tire pyrolysis units in the U.S. Since then, however, at least one facility, in Oregon, has commenced operation. Research and demonstration work by several entrepreneurs is described below ... 

Besides the companies listed above, who have indicated recent interest in tire pyrolysis ventures, there are also many companies who have done experimental work in tire pyrolysis in the past. Particularly noteworthy have been the efforts by Firestone and TOSCO. 

The U.S. Environmental Protection Agency s Control Technology Center recognizes the need for data describing the air quality impacts of two of these disposal options the controlled burning of tires to recover its fuel value and pyrolysis for fuel and carbon black. The purpose of this report is to summarize available air emissions and control data and information on tire pyrolysis and burning tires for fuel. 

Nearly all of the processes used for tire pyrolysis have the same basic unit operation, with variations in the reactor design. First, this chapter describes the basic process... 

The only raw material required for most tire pyrolysis processes is scrap tires. Some processors purchase and use whole tires, while others chip whole tires into two inch pieces, or purchase the tires already chipped. Conrad uses a local tire chipper to shred whole tires to a 2-inch size, wire-in, for their use. The tire chipper, who works on Conrad property, receives a tipping fee for collecting the tires, and provides the TDF to Conrad free of charge. 

Although there are hundreds of tire pyrolysis processes, they all can be categorized as either oxidative or reductive. Table 8-2 contains a list of manufacturers of oxidative and reductive processes with capacities, operating temperatures, and product mixes. 

The reductive process is the more traditional process for tire pyrolysis. This process excludes all sources of oxygen and relies on the reactor heat alone to decompose the tires. Some processors pressurize the reactor with an inert gas such as nitrogen to prevent air from leaking into the reactor, while some inject hydrogen to react with the sulfur present in the rubber in the tires to form hydrogen sulfide. Hydrogen sulfide can be recovered and sold as a by-product. 

As mentioned earlier, a number of different types of reactors have been tried in tire pyrolysis. Almost any vessel that can be sealed can be used as a pyrolysis reactor. Reactor design has a significant effect on the quality of char produced, due to a uniform temperature gradient, and the abrasion of the particles with one another. Some of the reactor types that have been used are ... 

During the past ten years, no less than 34 major pyrolysis projects have been proposed, designed, patented, licensed, or built (see Table 8-2). Only one or two are operational today, arguably, none on a commercial basis. Technically, tire pyrolysis is feasible but financially, it is very questionable. This section reviews some of the highlights of the financial analysis of the process and products. 

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