| OCR Text |
Show on the grate changes. Figure 7 shows the fuel side of the ACC system. Multiple flame scanners are used to locate the change from volatiles combustion to char combustion. Microwave transmitter/receivers are used to sense the depth of refuse on the drying grate and combustion grate. As these signals deviate from their set points, the grate and feeder speeds are adjusted to maintain a constant combustion profile. NOx CONTROL STRATEGIES NOx control strategies have been tested by Takuma on several commercial refuse-fired systems in Japan. They are as follows: o low excess air, ~ water injection, OJ urea injection ) flue gas recirculation (FGR). Figure 8 compares NOx emissions f~r low excess air, water injection, and urea injection to normal operation at an MSW combustor in Nagoya, Japan. Similarly, Figure 9 compares NOx emissions for low excess air, and FGR to normal operation at a MSW combustor in Tokyo, Japan. Low excess air operation is implemented by reducing the 02 setp?int for the Automatic Combustion Control (ACe) system. Airflows for the overfire air system are adjusted accordingly. Low excess air operation is capable of reducing NOx emissions up to 30 percent. As shown in Figure 8 water injection is moderately effective, reducing NOx emissions by 20 percent at normal excess air levels. However, when combined with low excess air firing the additional NOx reduction was 10 percent. Water injection is capable of achieving marginal reductions during low excess air firing alone, but flame instability and eo emissions during water injection limited reductions in excess 01130 4 |
