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Show Performance of Third Generation Rotary Kiln Incinerator John Petersen and Mike Keller Callidus Technologies Inc. times. A significant reduction in these gas flow peaks can be achieved by feed preparation and careful feeder selection, but the peaks cannot be totally eliminated. A second factor that complicates system operation is that solid fuels (waste materials) can take a considerable amount of time to burn. It is normal to design the kiln to include one hour's residence time for the solid material~this means that the system will continue to operate for some period of time after the waste feeding operation is suspended. Given that the hot refractory lined kiln contains significant amount of potential fuel at any given time, it is, therefore, impossible to control the available fuel to the process. Without control of the fuel, it is obvious that control of the combustion air is mandatory. With endothermic or slightly exothermic wastes (up to 2000 Btu/lb) control of the excess air level is generally sufficient to allow control of the process. However, with highly exothermic wastes such as plastics or hydrocarbon sludges, (over 5000 Btu/lb) excess air control alone is not adequate. To facilitate understanding of this fact, a simple temperature vs % air graph1 (Figure 1) is a useful tool. If the kiln is operating at 1800°F, in the ashing mode2 (the desired operating mode (2)) and a significant increase in fuel occurs, hydrocarbon volitization increases to produce combustible vapors. At this point two situations can occur. 1. If excess air is available, the temperature will rapidly climb as vapors combust and the increased temperature causes radiant flux to the waste fuel to increase as the fourth power of the absolute temperature. It is impractical to add additional quench air at a ratio sufficient to reduce this temperature in time to prevent a runaway temperature. In addition, at the same time the combustion rate is increasing, the amount of flue gas also increases to raise increase the amount of particulate entrainment V-33 3 |