OCR Text |
Show 10 -6 Baseline 0 < r/rQ < 0.125 -..._ 0.125 < r/rQ < 0.25 •»«-. n 9*> < r/r_ < 1 Baseline CC1. 1.0 Wtu/hr CC1. 1.2 Wtu/hr 0.25 < r/rn < 1 0 < r/rQ < 0.125 0.125 < r/rQ - 0.25 0.25 • r/r„ < 1 7 8 Zone number 10 1? Figure 11. Effect of Firing Rate on Three-Annuli Baseline CCI4 Destruction • Increases the near-exit temperatures, when the change in mass flowrate is proportionally greater than the change in wall heat loss. This is often the case with a large waterwall surface area The first and last effects tend to promote waste destruction, the second and third tend to inhibit it. Because of these competing effects, the result of increasing excess air for a given furnace type and operating regime is not readily obvious. Predicted destruction efficiency can increase with excess air level, decrease with excess air level, or show a relative maximum depending on the input parameters. Figure 12 shows the weighted average carbon tetrachloride breakthrough at 10 percent, 25 percent, and 50 percent excess air levels, with all other baseline conditions intact. In this case, the effect of oxygen availability dominates the destruction efficiency; the model predicts increasing destruction efficiency with increasing excess air level for this operating regime and furnace configuration. Particular care should be taken in not interpreting this trend as characteristic of all or even most waste types, furnace types, or firing conditions. The oxygen dependency in the kinetic expression has not been well defined by experiment. The oxygen exponent, a, for example, was arbitrarily chosen to have the value of 1. An oxygen exponent of less than 1 would result in a prediction of 5.5.23 |