Affect of System Operation on Toxic Air Emissions

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.«~... u.i a: ~ C/) C/) w a: a.. a: 0 a.. ~ 1200 -3 10 10 -4 -5 10 -6 10 -7 10 900 TEMPERATURE, ~ 1600 2000 2400 2800 3200 1300 1700 2100 TEMPERATURE, K Figure 3. Impact of temperature on the effective vapor pressure of several toxic metals. The quantity of chlorine in the waste has a significant effect on the vapor pressure of many metals. Figure 4 shows the behavior of two metals under typical combustion conditions. Generally, chlorides are more volatile than the corresponding metal oxides or uncombined metals. The effective vapor pressures of many metals increase as the concentration of chlorine increases and more of each metal is converted to metal chloride. However, once the metal has been completely converted into metal chloride, the presence of additional metal has no further effect on the vapor pressure of the metal. Heterogeneous and homogeneous condensation occur simultaneous I y at different rates. All the material that condenses homogeneously forms particles less than 1 mm in diameter. The size distribution of the material that condenses heterogeneously depends on the size distribution of the entrained particles. Some heterogenous condensation occurs on larger particles which flue gas cleaning equipment can effectively capture. Because of this, metal emissions increase as the ratio of homogeneous to heterogeneous condensation increases. -6-