Partitioning ofthe Refractory Metals, Nickel and Chromium, in Combustion Systems

The partitioning of nickel (Ni) and chromium (Cr) in a laboratory scale combustor was investigated theoretically and experimentally. Theoretical predictions based on chemical equilibrium indicate that chlorine significantly increases the volatility ofNi because of the formations of Ni-chloride compounds. Chlorine's predicted effecton Cr volatility at high temperatures ( > 700K) was minimal, although some volatile Cr-chloride compounds were predicted at low temperatures ( < 700 K). Experimental studies employed a 59kW laboratory scale combustor with a swirling natural gas diffusion flame through which aqueous Ni and Cr solutions were sprayed. Particle size distributions (PSDs) in the stack were measured by three different techniques: electrical mobility and inertial impaction for sampled aerosols and light scattering for in-situ analyses. All three methods produced consistent PSDs. Experimental data for Ni were also consistent with the theoretical predictions. and confirmed the large increase in Ni volatility due to chlorine. Also consistent with equilibria. experimental data for Cr(III, VI) failed to indicate notable increases in volatility due to chlorine addition. However, introducing Cr(VI) in the feed produced smaller Cr particles in the exhaust than did Cr(III). Experimental evidence suggests that, contrary to equilibrium predictions, Cr(VI) vaporized in the flame while Cr(lII) did not. This result, however, may not be related to the initial Cr valency but, rather, due to the particular choice of Cr(III) [Cr(NO3)3] and Cr(VI) [CrO3] species examined. Speciation of Cr in the exhaust, however, was independent of the initial Cr valency, with exhaust values of Cr(VI) typically less than 1% of the total Cr measured. Based on color and solubility, a large fraction ofthesampled Crwas believed to be Cr3O3. The Cr(VI) fraction in the exhaust was enhanced slightly by chlorine, but reduced to below analytical detection limits by the addition of small (stoichiometric with respect to Cr) quantities of sulfur.