Metal Aerosol Formation in a Laboratory Swirl Flame Incinerator

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Abstract
Experiments were performed on an 82 kW (280,000 Btu/hr) refractory-lined horizontal tunnel combustor to examine the aerosol particle size distribution (PSD) produced by simulated nickel, cadmium, and lead wastes injected into an incineration environment. Metal constituents in the form of aqueous solutions of nickel, cadmium, and lead nitrates were introduced as secondary sprays within a swirl stabilized natural gas diffusion flame. Aerosol size distributions were measured at stack locations using a differential mobility particle sizer and a cascade impactor as functions of combustor temperature and waste chlorine content. Cadmium and lead produced emissions of submicron metal aerosols with mass mean diameters of approximately 0.2 μm. These submicron aerosol PSDs are consistent with a mechanism of metal vaporization followed by nucleation, condensation, and coagulation prior to sampling. Nickel also formed submicron particles, but the PSD was not generally consistent with a vaporization mechanism. With chlorine present, the PSDs for all three metals were similar in shape, and could be interpreted in light of the effect of chlorine to enhance and prolong the presence of metals in the vapor phase, and leading to the sampling of a less mature aerosol than that seen under baseline conditions. The effect of chlorine on nickel partitioning was particularly significant, and is consistent with vapor pressure predictions.

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