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3.0 TIRES AS FUEL Tire-derived fuel (TDF) has been successfully utilized as a source of energy in cement and lime manufacturing, steam generation for electricity, and other industrial processes. Results of source test reports have been collected and are summarized by source type. Typical sources that have been successful in integrating TDF with other fuels are: • Cement Kilns; • Pulp and Paper Mills; • Utilities (including dedicated Tire-to-Energy facilities); and • General Industrial Boilers. TDF has long been recognized as a potential fuel. It compares favorably to coal, as presented in Table 16. It has a higher heating value than coal, and less moisture content. TDF contains more carbon, about as much sulfur as medium-sulfur coal, but much less fuel-bound nitrogen. Whether burning TDF in a new facility or as a modification to an existing facility, several issues must be considered. One consideration is the need convert scrap tires into a useable fuel. This requires a system to dewire, and shred, or otherwise size the tires so they can accommodated by a combustor. In addition to aiding in feeding, the sized fuel generally allows for more efficient combustion. However, some large combustor configurations, such as cement kilns, wet-bottom boilers, and stoker-grate boilers can be modified to accept whole tires. Modifications to hardware, combustion practices and/or other operating practices may also be necessary in order to burn TDF. These modifications are case-specific, and must be addressed by engineering staff when considering using TDF. 3.1 Laboratory Simulation of TDF Emissions Pilot-scale emissions testing of TDF was conducted in a 73 kW (250,000 BTU/hr) rotary kiln incinerator simulator (RKIS) in EPA's Environmental Research Center in Research Triangle Park, NC (Lemieux, 1994). This size simulator has been established as exhibiting the salient features of full-scale units with ratings 20 to 40 times larger. The test program was undertaken to provide assistance to state and local pollution agencies in establishing permitting guidelines and evaluating permit applications for facilities seeking to supplement its fuel with tires or TDF. A list of analytes would defer some of the expenses of stack sampling. The purposes of the test program were to (1) generate a profile of target analytes for guidance in preparing a full-scale stack sampling program and (2) provide insight into the technical issues related to controlled combustion of scrap tires. Because of the differences in scaling, such as gas-phase mixing phenomena and other equipment-specific factors, Lemieux specifically states that emission factors from the RKIS cannot be directly 30