Riley-Takuma Technology for Refuse Combustion Plants

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flow model testing conducted by Riley Stoker on a 1/12 scale model are illustrated in Figure 5. OFA entering downward over the drying grate creates a large stabilizing recirculation zone in the lower furnace. A small amount of OFA is added over the combustion grate from the rear OFA nozzles to raise the stoichiometry of the lower furnace. Air for final burnout is added in the upper furnace. It is this air, mixing with the furnace gases in the shear layer between the lower furnace recirculation and the air jet, that is most effective at reducing CO, total unburned hydrocarbon~. After leaving the furnace, the flue gases enter a dropout pass, which provides about 2 seconds residence time between 15000F and 16000 F. The dropout pass has been shown to reduce CO emissions by 80 to 96 percent. This results in low CO emissions even during furnace upsets. Central to the stable operation of a Riley-Takuma furnace is the Automatic Combustion Control (ACC) System. The ACC system is the result of twenty years of research by Takuma and its evolution is still progressing. The objectives of the ACC system are to provide constant steam flow, control combustion on the grate, and control emissions. Steam flow is controlled primarily by adjusting air flow to the combustion grate. This alters the rate of combustion in response to temporary changes in fuel composition. As the undergrate air flow and fuel flow change, excess air will change. The OFA flow is adjusted to maintain a constant O2 concentration in the flue gas and a constant furnace exit gas temperature. Undergrate air flow is adjusted to control large changes in 02 concentration. A schematic diagram of the air control portion of the ACC is shown in Figure 6. If a change in fuel composition continues then the combustion pattern 01130 3