OCR Text |
Show with kiln exit temperature increased from 816° to 871°C (1500° to 1600°F), the total afterburner exit flue gas particulate load shown in Table 4 increased from 13 to about 20 mg/m3 of flue gas, suggesting increased entrainment of particulate as the calculated average kiln flue gas velocity increased from 0.68 to 0.90 m/s. Little redistribution of the metals with the increased temperature is observed in the less than 4 ~m size fraction. The small increase in the total particulate fraction (to about 13 percent) in this range was accompanied by a similar increase in this fraction for most metals. There was a similar increase in the fraction of total particulate in the less than 10 ~m range with kiln temperature increased from 816° to 871°C (1500° to 1600°F). However, with the exception of chromium and bismuth, a much greater increase in the fraction of metals in this range is observed. Furthermore, Figure 2 shows that the redistribution of metals to this range generally correlated with the relative volatilities of the metals, in that metals with lower volatility temperatures were enriched to a greater degree in the less than 10 ~m particulate. It is interesting that the redistribution of metals to finer particulate size fractions with kiln temperature increased from 816° to 871°C (1500° to 1600°F) was seen in the less than 10 ~m size fraction but not in the less than 4 ~m size fraction. An explanation is found in Figure 4, which shows the fraction of total particulate accounted for by the less than 4 ~m, 4 to 10 ~m, 10 to 30 ~m, and greater than 30 ~m size fractions as a function of the test variables. Values for the three center point replicate test conditions (Tests 4, 5, and 6) were averaged and plotted as a single bar. The observed ranges for the three tests are indicated in the figure. The upper part of Figure 4 shows that, while the fraction of total particulate in the less than 4 ~m size range perhaps slightly increased with kiln temperature increased from 816° to 871°C (1500° to 1600°F), the fraction in the 4 to 10 ~m size range significantly increased with this temperature change. A corresponding increase in the surface area available to accommodate recondensing volatile metal in this size range would have occurred, with the result that general metal redistribution to this size range is possible. Note from Figure 4 that roughly 50 to 60 percent of the flue gas particulate in the afterburner exit was larger than 30 ~m. The large fraction of coarse particulate suggests that entrainment of solid material from the kiln bed was a major source of particulate in the flue gas. with kiln temperature further increased from 871° to 927°C (1600° to 1700°F), the afterburner exit flue gas particulate load shown in Table 4 increased from about 20 to 13 |