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Show The model was configured to represent typical hazardous waste incineration systems and used to assess the importance of many different operating parameters. The parameters found to be important include: • Metal type • Combustion chamber temperature • Waste chlorine content • Flue gas cleaning system operation These parameters were predicted to have a strong impact on metals behavior in waste combustion systems. Other parameters examined were predicted to have a weaker effect on metals behavior. These parameters include: • Waste sulfur content • Gas residence time • Entrained particle size distribution • Local oxygen concentration • Concentration of entrained particles • Gas cooling rate • Specific flue gas cleaning device operating parameters. The type of metal and the temperature of the burning waste have the strongest effects on the predicted behavior of metals. Figure 3 illustrates the impact of temperature on representative metals' effective vapor pressures. The effective vapor pressure is the sum of the vapor pressures of all species containing the metal of interest present at equilibrium weighted by their relative concentrations. As temperature increases, vapor pressure increases, resulting in increased metals emissions. Several features of the curves in Figure 3 warrant attention. First, the vapor pressures of all metals increase sharply with temperature. A ten-fold increase in the vapor pressure can result from a temperature increase as small as 20 K. Second, the vapor pressures vary widely from metal to metal. Third, all the vapor pressures shown are very small, typically less than 1 x 10-6 atm. This indicates that only a small quantity of each metal will vaporize. However, because of the enrichment of vaporized species on small particles, the ability of small particles to penetrate deep into the lung, and the toxicity of many of the metals, a small quantity of vaporized material is sufficient to be a potential health threat. -5- |