| OCR Text |
Show is set to unity at the center of the first zone. The calculation begins in the third zone, downstream of the zones occupied by the flame. The farther downstream of the flame, the more conservative the estimate of destruction efficiency. The shape of the radial temperature profiles is specified by the boundary layer thickness and polynomial order. For simplicity, the temperature is assumed to be constant across the center of the furnace and to drop off linearly at one-quarter of a radius from the wall. This is a reasonable representation of the experimental temperature data. The furnace is divided into three concentric annuli whose borders are one-eighth and one-quarter of a radius from the wall. Computational time is saved by selecting a small number of annuli, at the expense of a conservative DRE prediction. The pseudo first-order rate constants used for inputs to the model were taken from the literature (Ref. 11, 12). They were derived from the fixed temperature oxidation of dilute vapors of hazardous waste in air in a quartz tube flame reactor. The rate constants are not well suited to the furnace model because they do not include an oxygen-dependent term. An oxygen concentration term was added and appropriately adjusted. Table 5 shows the important components of the computer output for the baseline case. The four tables correspond to three annuli and the overall bulk flow results. Each table shows the cumulative residence time, temperature, and mass fraction waste breakthrough, C/CQ, at the center of each zone. The overall fractional breakthrough, under the "bulk flow" heading, is simply the average of each annular contribution, weighted by the flowrate through the annulus. In this case, the postflame gases in the furnace center temperature, and mass fraction waste breakthrough, C/CQ, at the center of each zone. The overall fractional breakthrough, under the "bulk flow" heading, is simply the average of each annular contribution, weighted by the flowrate through the annulus. In this case, the postflame gases in the furnace center promote 99.93 percent DRE at Zone 10 (6.875 ft from the front wall). However, the postflame gases along the wall promote only 99.12 percent DRE at Zone 10. The bulk flow table shows that the turbulent flow boundary layer shape was calculated for the baseline case, because the bulk Reynolds number exceeded 3,000. Figure 9 shows the baseline concentration profiles at each annulus plotted against axial position. The graph shows clearly that the cold walls quench waste conversion reactions in the postflame gases in the outermost 5.5.19 |
