OCR Text |
Show 28 mg/m3 of flue gas, reflecting additional entrainment of particulate as the calculated average kiln flue gas velocity further increased from about 0.90 to 1.13 mise The entrained particulate size distribution was not significantly altered, as shown in Figure 2. However, with this further increase in kiln temperature, a significant redistribution of all metals to particulate of less than 4 ~m is seen. The data shown in Figure 2 suggest that, as the kiln temperature increased, there may have been a selective redistribution of metals to sequentially finer particulate in the flue gas. In addition, the effect of kiln temperature on metal redistribution to finer particulate correlated with the relative volatility of the metals. More volatile metals were redistributed to a greater extent. with the exception of chromium, the average distributions of the metals in the flue gas particulate shifted from roughly 20 percent less than 10 ~m to roughly 60 percent less than 10 ~m with kiln temperature increased from 816 0 to 927°C (1500 0 to 1700°F). The corresponding shift for the total particulate sample was from 20 to about 30 percent. Similar metal enrichment behavior in the less than 4 ~m size fraction was observed. The test data indicate that kiln temperature increased over this range enriches the flue gas metals in the finer particulate size fractions. These data are significant given the greater challenge to air pollution control devices posed by smaller particulate, the ability of smaller particles to penetrate the deep lung, and the toxicity of many metals. However, the data also suggest that metal enrichment in the fine particulate fractions can be controlled operationally by limiting incinerator temperature. The observed enrichment of the flue gas particulate metals in the finer size fractions is expected based upon the strong relationship between metal vapor pressure and temperature. with increased kiln temperature, additional metal vaporization from both the kiln bed and the entrained particulate can occur. Under the volatilization/condensation mechanism, the additional vaporized metal is expected to condense primarily in the finer articulate size fractions. The effects of the waste feed chlorine content on total particulate and metal-specific size distributions are shown in Figure 3. When feed chlorine was increased from 0 to 4 percent, the fraction of total particulate in the less than 10 ~m fraction increased from 20 to about 35 percent. This is expected if the presence of chlorine in the feed serves to increase the volatility of some feed inorganic constituents. When reviewing the data, the effects of chlorine were taken to be most significant when the metal distributions were shifted more than the distributions of the total particulate sample. Thus, flue gas particulate size distributions for barium and strontium and, to a lesser extent, arsenic, bismuth and magnesium, were not significantly affected by waste feed 15 |