Tire combustion

EPA 1997. Air Emissions from Scrap Tire Combustion. US Environmental Protection Agency, EPA-600/ R-97-115. 

The largest scrap tires combustion system is the Oxford Energy plant in Modesto, California. It consumes about 4.9 million tires per year and generates 14 MW of power. A second Oxford Energy power plant, designed to burn about 9-10 million tires per year, is under construction in Connecticut. Commercial operation is planned for 1991. 

Seven cement kilns in the United States utilize about 6 million scrap tires per year to replace conventional fuels. Cement kilns appear to be ideal for scrap tires because of their high operating temperatures (2,600 F) and good conditions for complete combustion, which minimize air pollution problems. Also, there is no residue, since the ash is incorporated into the cement product. Of the 240 cement kilns in the United States, about 50 are equipped with precalciner/preheaters, making them most suitable for tire combustion. 

The main noneconomic barriers to scrap tire combustion are the time required for permitting a plant and the concerns of neighbors regarding environmental, health, and safety issues. Because of the test bums required and time delays in permitting, many cement plant and pulp and paper mill operators hesitate to change their operation for the small savings realized by burning scrap tires. 

Scrap tire combustion is practiced in power plants, tire manufacturing plants, cement kilns, pulp and paper plants, and small package steam plants. 

The largest tire combustion facility in the world is now beginning construction-the Oxford Energy power plant at Sterling Connecticut, which will burn 9-10 million tires per year. When it is completed, it will bring the total of tires annually combusted for fuel to approximately 30 million. 

Since tires have a Btu value comparable to the best coal, they would be expected to be an economically attractive fuel in some situations. Recent U.S. experience has shown economic feasibility for tire-to-energy power plants and for tdf used in cement kilns and pulp and paper mills. The economic barriers facing these types of tire combustion will be discussed below. Despite these economic barriers, the use of tdf has increased over the last year, and this trend is expected to continue. 

As discussed above, there are currently operating facilities where the combustion of tires and tdf has proven to be profitable. The economic feasibility of tires-to-energy plants depends on the buy-back rate for the electricity. For tdf consumed at cement kilns or pulp and paper mills, the economic feasibility depends on cost savings over competing fuels. Only a substantial annual cost savings justifies modifying a plant to handle tdf. The next section discusses the noneconomic barriers that must be considered once it has been determined that tire combustion is economically feasible. 

Noneconomic barriers to scrap tire combustion include problems in siting new facilities and environmental concerns. These two types of noneconomic barriers are related since objections to siting are usually due to perceived environmental problems. These noneconomic barriers are discussed below for power plants and tire derived fuel usage. 

Oirly afew formation reactions can actually be carried out, and therefore datafor tlrese reactions must usually be detenrrined indirectly. One kind of reaction that readily lends itself to experiment is tire combustion reaction, and nrairy standard heats of fonrration come from standard. 

Tlris of conrse is tire combustion reactioir of hydrogen, bnt coirrbnstioir iir tire sense of bunring does not occnr iir the cell. 

Winter-type smog, characterized by high concentrations of SO2 and PM that arise mainly from tire combustion of coal and fuels with a high content of sulfur. This kind of pollution occurs in urban areas witli many power plants or industrial units clustered together, where low temperatures and mist are observed in the year. It has been also termed industrial pollution. ... 

Combustion reactions are rapid reactions that produce a flame. Most of tire combustion reactions we observe involve O2 from air as a reactant. Equation 3.5 and Practice Exercise 3.1(b) illustrate a general class of reactions involving tire burning or combustion of hydrocarbon compounds (compounds fliat contain only carbon and hydrogen, such as CH4 and C2H4). (S tion 2.9)... 

There are over 280 million scrap tires produced annually in the United States. Of these over 100 million are used as fuel and most of these are burnt to supplement fuel use in cement and other rotary kiln operations. The cement process is particularly convenient for tire combustion because the reinforced steel wire in the tire tread can be a source of iron for the cement chemistry. Kilns burning tires must comply with the EPA s boiler and industrial furnace act and hence are heavily regulated as a pollution source. Table 6.3 gives a typical average composition of tires supplied by the Rubber Manufacturers Association of America. 

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