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extrapolated to full-scale units. Furthermore, there are significant differences between kilns and other combustion devices, such as boilers, and the study does not address these issues. Nevertheless, the simulator is useful in examining the fundamental phenomena of TDF combustion and to gain an understanding of the qualitative trends that would be found in a full-scale rotary kiln. The TDF tested was wire-free crumb rubber sized to <0.64 cm (<1/4 in.). It was combusted at several combinations of feed rate, temperature, and kiln oxygen concentration. The TDF was combusted with natural gas as the primary fuel. Samples were taken to examine volatile and semi-volatile organics, PCDD/PCDF, and metal aerosols. Data were collected to determine the effects of feed rates, type of feeding, i.e., continuous versus batch, and combustion controls on emissions. The data were taken in the exhaust stream prior to any add-on air pollution control devices. The study addressed two issues: (1) the influence of the mode of tire feeding, for example, whole tires versus shredded tires, on the PICs, and (2) the potential for air toxic emissions not normally found when burning conventional fuels. The TDF material used in the test program was analyzed and the proximate and ultimate analyses and metals analysis results are presented in Table 17. TDF contains significant amounts of zinc, since zinc is used extensively in the tire manufacturing process. In all, thirty test conditions were run, with the TDF feed rate varying from 0% to 21.4% of heat input. The test conditions were achieved by varying kiln firing rate, combustion air flow rate, and tire feed rate. The majority of the tests were conducted with a steady-state feed of TDF. Variations in the mode of TDF feeding were evaluated in two tests. In one test, the kiln air flow rate was ramped up and down every 10 minutes ("ramp") to change the kiln oxygen concentration to simulate transient operation. In the other, TDF was introduced in 300 g batches spaced ten minutes apart ("batch") to simulate transient operation, such as feeding whole tires at periodic intervals. VOCs were collected by a Volatile Organic Sampling Train (VOST) and analyzed with a gas chromatograph/mass spectrometer (GC/MS). The majority of the VOCs were very near to or below the detection limits of the equipment. Estimated emissions of VOCs for five representative test runs are presented in Table 18. PAHs were analyzed with a Continuous Emission Monitor (CEM) PAH analyzer. PAH emissions were fairly insensitive to temperature and oxygen for the range of conditions studied, however, increasing TDF feed rates tended to increase PAH emissions for all oxygen levels. Overall, it was observed that supplementing natural gas with TDF tended to increase PAH emissions, but not dramatically, provided that steady-state operation is maintained. Semi-volatile organic compounds (SVOC) and bulk particulate were collected by isokinetic sampling protocols with a Modified Method 5 (MM5) train. Data from the analyses did not indicate that SVOC were present in detectable concentrations. Lemieux 32