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Show air. In addition, the latent heat of varporization of the water reduces the thermodynamic efficiency of the system. Figure 8 also shows that urea injection is very effective at reducing NOx• NOx is reduced by 40 percent under low excess air conditions. However, the nature of the process requires about 50 percent more than the theoretical urea required resulting in ammonia slip, or leakage out the stack. In addition, since water is used as a carrier for the urea, the same flame stability and efficiency problems occur. Figure 9 shows that FGR at an MSW facility in Tokyo is capable of reducing NOx by 20 percent during normal operation and 30 percent during low excess air operation. Unlike water injection and urea injection, which use water as a carrier, FGR can improve the operation of the MSW combustor during low excess air firing. In the Tokyo facility, FGR has been introduced successfully through the OFA system displacing excess air without disturbing the furnace mixing patterns. FGR has also been introduced simultaneously through both the OFA system and the undergrate air system. However, introducing the flue gas through the stoker grates Significantly increases the amount of combustible material in the furnace bottom ash. To date, low excess air firing and FGR are still the preferred MSW combustion control method of NOx reduction in Japan (20. However, emissions of trace organics may limit their application in the United States. EMISSIONS REDUCTION USING NATURAL GAS Riley Research is currently working with the Institute of Gas Technology (IGT) and the Gas Resear.ch Institute (GRI) on a program to evaluate emissions reduction from municipal solid waste (MSW) combustors using natural gas. The objective of the program is to investigate the use of natural gas co-firing in combination with low 01130 5 |
